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aus+uk / uk.tech.digital-tv / What shape are pixels?

SubjectAuthor
* What shape are pixels?Brian Gaff \(Sofa\)
+* Re: What shape are pixels?R. Mark Clayton
|+- Re: What shape are pixels?Brian Gaff \(Sofa\)
|`* Re: What shape are pixels?Richard Tobin
| `* Re: What shape are pixels?David Woolley
|  +* Re: What shape are pixels?Richard Tobin
|  |`* Re: What shape are pixels?Dave W
|  | +- Re: What shape are pixels?R. Mark Clayton
|  | `- Re: What shape are pixels?Brian Gaff \(Sofa\)
|  `* Re: What shape are pixels?Brian Gaff \(Sofa\)
|   `* Re: What shape are pixels?NY
|    +- Re: What shape are pixels?R. Mark Clayton
|    +* Re: What shape are pixels?Java Jive
|    |`* Re: What shape are pixels?NY
|    | +* Re: What shape are pixels?Roderick Stewart
|    | |+* Re: What shape are pixels?charles
|    | ||+* Re: What shape are pixels?williamwright
|    | |||`* Re: What shape are pixels?NY
|    | ||| `* Re: What shape are pixels?Roderick Stewart
|    | |||  `* Re: What shape are pixels?NY
|    | |||   `* Re: What shape are pixels?Roderick Stewart
|    | |||    `* Re: What shape are pixels?David Woolley
|    | |||     +- Re: What shape are pixels?williamwright
|    | |||     `* Re: What shape are pixels?NY
|    | |||      `- Re: What shape are pixels?Roderick Stewart
|    | ||`* Re: What shape are pixels?Mark Carver
|    | || `* Re: What shape are pixels?charles
|    | ||  `* Re: What shape are pixels?Mark Carver
|    | ||   +- Re: What shape are pixels?charles
|    | ||   `* Re: What shape are pixels?Paul Ratcliffe
|    | ||    `- Re: What shape are pixels?david lan
|    | |`* Re: What shape are pixels?Max Demian
|    | | `* Re: What shape are pixels?NY
|    | |  +- Re: What shape are pixels?Roderick Stewart
|    | |  `- Re: What shape are pixels?Max Demian
|    | `* Re: What shape are pixels?NY
|    |  `- Re: What shape are pixels?Java Jive
|    `* Re: What shape are pixels?williamwright
|     `* Re: What shape are pixels?Roderick Stewart
|      `- Re: What shape are pixels?NY
`* Re: What shape are pixels?R. Mark Clayton
 `- Re: What shape are pixels?Brian Gaff \(Sofa\)

Pages:12
What shape are pixels?

<t14c7c$ou8$1@dont-email.me>

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From: bria...@blueyonder.co.uk (Brian Gaff \(Sofa\))
Newsgroups: uk.tech.digital-tv
Subject: What shape are pixels?
Date: Sat, 19 Mar 2022 10:44:55 -0000
Organization: A noiseless patient Spider
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 by: Brian Gaff \(Sofa\) - Sat, 19 Mar 2022 10:44 UTC

May seem a daft question, but in the old days of tubes, there were various
patterns of shadow masks on them. Some tended to be noticeable as vertical
stripes, others as little triads, And when we started to get digital video
as in games, it was not unusual to see oval circles on things, due to the
pixel being displayed oblong instead of square, so to speak.
Brian

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Re: What shape are pixels?

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Subject: Re: What shape are pixels?
From: notyalck...@gmail.com (R. Mark Clayton)
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 by: R. Mark Clayton - Sun, 20 Mar 2022 17:29 UTC

On Saturday, 19 March 2022 at 10:45:02 UTC, Brian Gaff (Sofa) wrote:
> May seem a daft question, but in the old days of tubes, there were various
> patterns of shadow masks on them. Some tended to be noticeable as vertical
> stripes, others as little triads, And when we started to get digital video
> as in games, it was not unusual to see oval circles on things, due to the
> pixel being displayed oblong instead of square, so to speak.
> Brian
>
>
>
> --
>
> This newsgroup posting comes to you directly from...
> The Sofa of Brian Gaff...
> bri...@blueyonder.co.uk
> Blind user, so no pictures please
> Note this Signature is meaningless.!

Old CRT's - dots illuminated by electron beam through a shadow mask
Trinitron - lines illuminated by electron beam through wires
Plasma - dots illuminated by plasma from "points" behind"
Most LCD - rectangular, sometimes with extra colours (e.g. Sharp), usually arrayed, but on vertical alignment models they are vertical bars. Great picture, although slow response (so not for gamers)
OLED - dunno, but probably an array.
Micro LED - little LED chips usually arrayed.

On 4k monitors or TV's at a sensible distance it is quite hard to make out the pixels.

Re: What shape are pixels?

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From: bria...@blueyonder.co.uk (Brian Gaff \(Sofa\))
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Mon, 21 Mar 2022 08:02:28 -0000
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 by: Brian Gaff \(Sofa\) - Mon, 21 Mar 2022 08:02 UTC

Well I cannot see them these days of course, but I guess the circle problem
then was when early display electronics did not all use the same aspect
ratio effectively widening or narrowing pixels. I can well remember tat my
ZX Spectrum on a standard TV was correct , but when you ran other computers
of the time with simulated code to run spectrum games, ie all were z80 chip
based, you often found that the display was a different aspect ratio,
creating the issue. Memotech, and Sam Coupe machines both had this issue as
one used a Texas chip for the display, the other aULA made by Fujitsu.
Brian

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"R. Mark Clayton" <notyalckram@gmail.com> wrote in message
news:9b8a1314-4767-4a74-9097-af16b836ed71n@googlegroups.com...
> On Saturday, 19 March 2022 at 10:45:02 UTC, Brian Gaff (Sofa) wrote:
>> May seem a daft question, but in the old days of tubes, there were
>> various
>> patterns of shadow masks on them. Some tended to be noticeable as
>> vertical
>> stripes, others as little triads, And when we started to get digital
>> video
>> as in games, it was not unusual to see oval circles on things, due to the
>> pixel being displayed oblong instead of square, so to speak.
>> Brian
>>
>>
>>
>> --
>>
>> This newsgroup posting comes to you directly from...
>> The Sofa of Brian Gaff...
>> bri...@blueyonder.co.uk
>> Blind user, so no pictures please
>> Note this Signature is meaningless.!
>
> Old CRT's - dots illuminated by electron beam through a shadow mask
> Trinitron - lines illuminated by electron beam through wires
> Plasma - dots illuminated by plasma from "points" behind"
> Most LCD - rectangular, sometimes with extra colours (e.g. Sharp), usually
> arrayed, but on vertical alignment models they are vertical bars. Great
> picture, although slow response (so not for gamers)
> OLED - dunno, but probably an array.
> Micro LED - little LED chips usually arrayed.
>
> On 4k monitors or TV's at a sensible distance it is quite hard to make out
> the pixels.

Re: What shape are pixels?

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From: rich...@cogsci.ed.ac.uk (Richard Tobin)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Mon, 21 Mar 2022 12:24:10 +0000 (UTC)
Organization: Language Technology Group, University of Edinburgh
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 by: Richard Tobin - Mon, 21 Mar 2022 12:24 UTC

In article <9b8a1314-4767-4a74-9097-af16b836ed71n@googlegroups.com>,
R. Mark Clayton <notyalckram@gmail.com> wrote:
>OLED - dunno, but probably an array.

Looking at mine through a rather poor-quality USB digital microscope,
each rectangular pixel appears to consist of 4 rectangular
colours, RGB and white, presumably the LEDs themselves.

https://www.cogsci.ed.ac.uk/~richard/oled-pixels.jpg

-- Richard

Re: What shape are pixels?

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From: dav...@ex.djwhome.demon.invalid (David Woolley)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Mon, 21 Mar 2022 12:49:46 +0000
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 by: David Woolley - Mon, 21 Mar 2022 12:49 UTC

On 21/03/2022 12:24, Richard Tobin wrote:
> RGB and white, presumably the LEDs themselves.

LEDs can't be white. What are called "white LEDs" are blue LEDs with a
yellow phosphor. They generate a relatively narrow band blue, from the
LED, and a very broadband yellow, from the phosphor. Unpowered I'd
expect "white" LEDs to look yellow.

Re: What shape are pixels?

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From: rich...@cogsci.ed.ac.uk (Richard Tobin)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Mon, 21 Mar 2022 14:31:29 +0000 (UTC)
Organization: Language Technology Group, University of Edinburgh
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 by: Richard Tobin - Mon, 21 Mar 2022 14:31 UTC

In article <t19s9b$3r1$1@dont-email.me>,
David Woolley <david@ex.djwhome.demon.invalid> wrote:

>> RGB and white, presumably the LEDs themselves.

>LEDs can't be white. What are called "white LEDs" are blue LEDs with a
>yellow phosphor. They generate a relatively narrow band blue, from the
>LED, and a very broadband yellow, from the phosphor. Unpowered I'd
>expect "white" LEDs to look yellow.

Apparently the RGB ones are R, G and B either. They are "white" OLEDs
with filters over them.

https://www.oled-info.com/lgs-wrgb-oled-tv-sub-pixels-captured-macro-photo

I guess WRGB is just the additive equivalent of CMYK.

-- Richard

Re: What shape are pixels?

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From: davew...@yahoo.co.uk (Dave W)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
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 by: Dave W - Mon, 21 Mar 2022 17:41 UTC

On Mon, 21 Mar 2022 14:31:29 +0000 (UTC), richard@cogsci.ed.ac.uk
(Richard Tobin) wrote:
>In article <t19s9b$3r1$1@dont-email.me>,
>David Woolley <david@ex.djwhome.demon.invalid> wrote:
>
>>> RGB and white, presumably the LEDs themselves.
>
>>LEDs can't be white. What are called "white LEDs" are blue LEDs with a
>>yellow phosphor. They generate a relatively narrow band blue, from the
>>LED, and a very broadband yellow, from the phosphor. Unpowered I'd
>>expect "white" LEDs to look yellow.
>
>Apparently the RGB ones are R, G and B either. They are "white" OLEDs
>with filters over them.
>
>https://www.oled-info.com/lgs-wrgb-oled-tv-sub-pixels-captured-macro-photo
>
>I guess WRGB is just the additive equivalent of CMYK.
>
>-- Richard
My TV has vertical strips, all composed of RGB pixels horizontally
arranged. When all three are on it looks white.
--
Dave W

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
From: notyalck...@gmail.com (R. Mark Clayton)
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 by: R. Mark Clayton - Mon, 21 Mar 2022 18:09 UTC

On Monday, 21 March 2022 at 17:42:01 UTC, Dave W wrote:
> On Mon, 21 Mar 2022 14:31:29 +0000 (UTC), ric...@cogsci.ed.ac.uk
> (Richard Tobin) wrote:
>
> >In article <t19s9b$3r1$1...@dont-email.me>,
> >David Woolley <da...@ex.djwhome.demon.invalid> wrote:
> >
> >>> RGB and white, presumably the LEDs themselves.
> >
> >>LEDs can't be white. What are called "white LEDs" are blue LEDs with a
> >>yellow phosphor. They generate a relatively narrow band blue, from the
> >>LED, and a very broadband yellow, from the phosphor. Unpowered I'd
> >>expect "white" LEDs to look yellow.
> >
> >Apparently the RGB ones are R, G and B either. They are "white" OLEDs
> >with filters over them.
> >
> >https://www.oled-info.com/lgs-wrgb-oled-tv-sub-pixels-captured-macro-photo
> >
> >I guess WRGB is just the additive equivalent of CMYK.
> >
> >-- Richard
> My TV has vertical strips, all composed of RGB pixels horizontally
> arranged. When all three are on it looks white.
> --
> Dave W

On a CRT that was Trinitron, on a flat panel it is VA.

Re: What shape are pixels?

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From: bria...@blueyonder.co.uk (Brian Gaff \(Sofa\))
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Tue, 22 Mar 2022 07:58:54 -0000
Organization: A noiseless patient Spider
Lines: 34
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 by: Brian Gaff \(Sofa\) - Tue, 22 Mar 2022 07:58 UTC

I do remember its all to do with colour temperature and lumins, something I
never bothered about when I could see. All I remember was early LEDs that
looked white to the naked eye seemed to look bluish when they were used
daylight around and that most fluorescent tubes looked dotty or yellow. If
you shot pictures with a video in such environments, the latter turned
everyone's faces green unless you changed the tint on the camera, and the
former looked a bit like blue light shown through mud is the best way I can
describe it. It does show up how clever the eye and brain are when they work
correctly to getting the colours to look right, wheas electronic devices
show what is really there.
I remember taking non flash photos under those orange street lights with
some very alien looking results. Some cars almost shone, yet others were
really black even when blue.
Some headlights were greeny yellow,while others were just whitish.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"David Woolley" <david@ex.djwhome.demon.invalid> wrote in message
news:t19s9b$3r1$1@dont-email.me...
> On 21/03/2022 12:24, Richard Tobin wrote:
>> RGB and white, presumably the LEDs themselves.
>
> LEDs can't be white. What are called "white LEDs" are blue LEDs with a
> yellow phosphor. They generate a relatively narrow band blue, from the
> LED, and a very broadband yellow, from the phosphor. Unpowered I'd expect
> "white" LEDs to look yellow.

Re: What shape are pixels?

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From: bria...@blueyonder.co.uk (Brian Gaff \(Sofa\))
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Tue, 22 Mar 2022 08:06:11 -0000
Organization: A noiseless patient Spider
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 by: Brian Gaff \(Sofa\) - Tue, 22 Mar 2022 08:06 UTC

As I recall, some issues with displays used to be that golden things and
things that reflected the sun like glint from water, never did work well on
tv, whether the issue was dynamic range on the camera or somewhere in the
chain, ormaybe in the display is hard to tell.
The old test of panning a spot so it momentarily shone in the camera used
to look really kind of flat compared to the real thing on your eye.
However, somebody I knew who had a Sharp TV some years ago, reckoned his
TV made a better job of glint than most. I suspect that might be a bit of
fakery going on with that extra led or whatever they were using which was a
pale orange fooling te eye maybe being controlled by software. I wish I
could have seen it.
The Best CRT pictures I ever saw were from Hitachi larger tvs, but you
needed a crane to lift them!

Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"Dave W" <davewi11@yahoo.co.uk> wrote in message
news:l3eh3hlhimlf4234rodd7mhkd9uc06m9q8@4ax.com...
> On Mon, 21 Mar 2022 14:31:29 +0000 (UTC), richard@cogsci.ed.ac.uk
> (Richard Tobin) wrote:
>
>>In article <t19s9b$3r1$1@dont-email.me>,
>>David Woolley <david@ex.djwhome.demon.invalid> wrote:
>>
>>>> RGB and white, presumably the LEDs themselves.
>>
>>>LEDs can't be white. What are called "white LEDs" are blue LEDs with a
>>>yellow phosphor. They generate a relatively narrow band blue, from the
>>>LED, and a very broadband yellow, from the phosphor. Unpowered I'd
>>>expect "white" LEDs to look yellow.
>>
>>Apparently the RGB ones are R, G and B either. They are "white" OLEDs
>>with filters over them.
>>
>>https://www.oled-info.com/lgs-wrgb-oled-tv-sub-pixels-captured-macro-photo
>>
>>I guess WRGB is just the additive equivalent of CMYK.
>>
>>-- Richard
>
> My TV has vertical strips, all composed of RGB pixels horizontally
> arranged. When all three are on it looks white.
> --
> Dave W
>

Re: What shape are pixels?

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From: me...@privacy.invalid (NY)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Tue, 22 Mar 2022 09:52:04 -0000
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 by: NY - Tue, 22 Mar 2022 09:52 UTC

"Brian Gaff (Sofa)" <briang1@blueyonder.co.uk> wrote in message
news:t1bvk0$l4s$1@dont-email.me...
> I do remember its all to do with colour temperature and lumins, something
> I never bothered about when I could see. All I remember was early LEDs
> that looked white to the naked eye seemed to look bluish when they were
> used daylight around and that most fluorescent tubes looked dotty or
> yellow. If you shot pictures with a video in such environments, the latter
> turned everyone's faces green unless you changed the tint on the camera,
> and the former looked a bit like blue light shown through mud is the best
> way I can describe it. It does show up how clever the eye and brain are
> when they work correctly to getting the colours to look right, wheas
> electronic devices show what is really there.
> I remember taking non flash photos under those orange street lights with
> some very alien looking results. Some cars almost shone, yet others were
> really black even when blue.
> Some headlights were greeny yellow,while others were just whitish.

Any lights with discontinuous spectrums (as opposed to "black body
radiation", as taught in physics A level) will appear differently depending
on the ways the RGB sensors respond to light.

I found that, to the naked eye, "daylight white" CFL bulbs looked
beautifully white and matched daylight coming in through windows. But some
digital cameras rendered them as very yellow - almost as much as tungsten
bulbs - whereas the same camera, with fixed 5000 K "sunlight" white balance,
rendered "warm white" fluorescent tubes as being less yellow and more blue
even though to the eye they looked warm compared with sunlight.

Most colour slide film (Kodachrome, Ektachrome) rendered fluorescent tubes
(probably warm white) as a horrible sickly green which the naked eye could
not detect. You could get filters for various types of film which corrected
for this.

I found that digital cameras with auto white balance correction, where you
point the camera at something white and tell it "this is white", give pretty
good rendition of colours in a variety of light sources. The main difference
with CFLs and LEDs, compared with tungsten and sun/shade daylight, is that
certain shades of red look too dark even though the overall colour balance
is correct.

https://i.postimg.cc/c4TW1zT4/daylight.jpg
https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
https://i.postimg.cc/NfQYct6z/Led.jpg
https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg

Are a series of photos of the front cover of an edition of the Radio Times,
with a pack of screw that have a saturated red label and a pack of drill
bits that have a royal blue case - so there's a good range of tones. I
illuminated it by various light sources, as described in the filename. and
auto-white-balanced the camera from light reflected off a sheet of A4
printer paper, lit with the same light source - apart from one case where I
used a warm-white fluorescent tube and deliberately set the camera to
sunlight WB.

I realise that Brian can't see this. The general colour balance and colour
cast for daylight, daylight CFL, LED and (warm) white fluorescent is pretty
consistent, though the red panel on the box of screws is much brighter on
daylight than on any of the artificial sources. The fluorescent with the
camera set for daylight has a pale yellow tint, though nowhere near as the
very strong reddish yellow that you'd get with a tungsten bulb.

One of the things you need to be careful of with LEDs is that they are
pulsed at high frequency with a mark:space ratio which varies as you dim the
light. This can lead to horizontal bands on photos if the camera sensor
reads the brightness of each row of pixels in turn, and the LEDs were on for
some rows and off for others. I presume when LEDs are used to illuminate a
TV studio they are driven from DC, with control over the current to dim the
light, so they do not turn on and off.

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
From: notyalck...@gmail.com (R. Mark Clayton)
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 by: R. Mark Clayton - Tue, 22 Mar 2022 12:13 UTC

On Tuesday, 22 March 2022 at 09:52:31 UTC, NY wrote:
> "Brian Gaff (Sofa)" <bri...@blueyonder.co.uk> wrote in message
> news:t1bvk0$l4s$1...@dont-email.me...
> > I do remember its all to do with colour temperature and lumins, something
> > I never bothered about when I could see. All I remember was early LEDs
> > that looked white to the naked eye seemed to look bluish when they were
> > used daylight around and that most fluorescent tubes looked dotty or
> > yellow. If you shot pictures with a video in such environments, the latter
> > turned everyone's faces green unless you changed the tint on the camera,
> > and the former looked a bit like blue light shown through mud is the best
> > way I can describe it. It does show up how clever the eye and brain are
> > when they work correctly to getting the colours to look right, wheas
> > electronic devices show what is really there.
> > I remember taking non flash photos under those orange street lights with
> > some very alien looking results. Some cars almost shone, yet others were
> > really black even when blue.
> > Some headlights were greeny yellow,while others were just whitish.
> Any lights with discontinuous spectrums (as opposed to "black body
> radiation", as taught in physics A level) will appear differently depending
> on the ways the RGB sensors respond to light.
>
> I found that, to the naked eye, "daylight white" CFL bulbs looked
> beautifully white and matched daylight coming in through windows. But some
> digital cameras rendered them as very yellow - almost as much as tungsten
> bulbs - whereas the same camera, with fixed 5000 K "sunlight" white balance,
> rendered "warm white" fluorescent tubes as being less yellow and more blue
> even though to the eye they looked warm compared with sunlight.
>
> Most colour slide film (Kodachrome, Ektachrome) rendered fluorescent tubes
> (probably warm white) as a horrible sickly green which the naked eye could
> not detect. You could get filters for various types of film which corrected
> for this.
>
> I found that digital cameras with auto white balance correction, where you
> point the camera at something white and tell it "this is white", give pretty
> good rendition of colours in a variety of light sources. The main difference
> with CFLs and LEDs, compared with tungsten and sun/shade daylight, is that
> certain shades of red look too dark even though the overall colour balance
> is correct.
>
> https://i.postimg.cc/c4TW1zT4/daylight.jpg
> https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
> https://i.postimg.cc/NfQYct6z/Led.jpg
> https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
> https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg
>
> Are a series of photos of the front cover of an edition of the Radio Times,
> with a pack of screw that have a saturated red label and a pack of drill
> bits that have a royal blue case - so there's a good range of tones. I
> illuminated it by various light sources, as described in the filename. and
> auto-white-balanced the camera from light reflected off a sheet of A4
> printer paper, lit with the same light source - apart from one case where I
> used a warm-white fluorescent tube and deliberately set the camera to
> sunlight WB.
>
> I realise that Brian can't see this. The general colour balance and colour
> cast for daylight, daylight CFL, LED and (warm) white fluorescent is pretty
> consistent, though the red panel on the box of screws is much brighter on
> daylight than on any of the artificial sources. The fluorescent with the
> camera set for daylight has a pale yellow tint, though nowhere near as the
> very strong reddish yellow that you'd get with a tungsten bulb.
>
> One of the things you need to be careful of with LEDs is that they are
> pulsed at high frequency with a mark:space ratio which varies as you dim the
> light. This can lead to horizontal bands on photos if the camera sensor
> reads the brightness of each row of pixels in turn, and the LEDs were on for
> some rows and off for others. I presume when LEDs are used to illuminate a
> TV studio they are driven from DC, with control over the current to dim the
> light, so they do not turn on and off.

Depends a bit on the phosphors. Philips due tri-phosphor tubes which give a much more balanced light.

Re: What shape are pixels?

<t1cmph$u4e$1@dont-email.me>

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From: jav...@evij.com.invalid (Java Jive)
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Subject: Re: What shape are pixels?
Date: Tue, 22 Mar 2022 14:34:22 +0000
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 by: Java Jive - Tue, 22 Mar 2022 14:34 UTC

On 22/03/2022 09:52, NY wrote:
>
> "Brian Gaff (Sofa)" <briang1@blueyonder.co.uk> wrote in message
> news:t1bvk0$l4s$1@dont-email.me...
>>
>> I do remember its all  to do with colour temperature and lumins,
>> something I never bothered about when I could see. All I remember was
>> early LEDs that looked white to the naked eye seemed to look bluish
>> when they were used daylight around and that most fluorescent tubes
>> looked dotty or yellow. If you shot pictures with a video in such
>> environments, the latter turned everyone's faces green unless you
>> changed the tint on the camera, and the former looked a bit like blue
>> light shown through mud is the best way I can describe it. It does
>> show up how clever the eye and brain are when they work correctly to
>> getting the colours to look right, wheas electronic devices show what
>> is really there.
>> I remember taking non flash photos under those orange street lights
>> with some very alien looking results. Some cars almost shone, yet
>> others were really black even when blue.
>> Some headlights were greeny yellow,while others were just whitish.
>
> Any lights with discontinuous spectrums (as opposed to "black body
> radiation", as taught in physics A level) will appear differently
> depending on the ways the RGB sensors respond to light.

Yes, while the sodium street lights that Brian refers to are
predominantly yellow, because the spectrum of sodium has a pair of very
bright yellow lines, in fact there are other colours in there as well -
although it's long time since I looked at the spectrum of one of those
lamps as part of a lab experiment, I remember some fainter red and green
lines as well. [Searches] Yes, lovely photo of the spectrum here,
though I'm not sure why the areas between the radiation lines aren't
black as they were in the experiment that I ran:

https://en.wikipedia.org/wiki/Sodium#/media/File:Sodium_spectrum_visible.png

> [snip]
>
> I found that digital cameras with auto white balance correction, where
> you point the camera at something white and tell it "this is white",
> give pretty good rendition of colours in a variety of light sources. The
> main difference with CFLs and LEDs, compared with tungsten and sun/shade
> daylight, is that certain shades of red look too dark even though the
> overall colour balance is correct.
>
> https://i.postimg.cc/c4TW1zT4/daylight.jpg
> https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
> https://i.postimg.cc/NfQYct6z/Led.jpg
> https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
> https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg

Interesting. Only the last of those looks truly awful. However, can I
offer some advice? Next time use a tripod to ensure that the setup of
each shot is identical. As you suggest most photo/scanning equipment
uses correction technologies of some sort, even if it's only as
unsophisticated as 'integrate to grey' in a film-era photo lab's
printing machine, and therefore, theoretically at least, varying the
composition might alter any auto-corrections applied by the equipment
used, and hence the result not be a comparison only of the light source
used, though I admit that such is not apparent in the shots you have linked.

> One of the things you need to be careful of with LEDs is that they are
> pulsed at high frequency with a mark:space ratio which varies as you dim
> the light. This can lead to horizontal bands on photos if the camera
> sensor reads the brightness of each row of pixels in turn, and the LEDs
> were on for some rows and off for others. I presume when LEDs are used
> to illuminate a TV studio they are driven from DC, with control over the
> current to dim the light, so they do not turn on and off.

You get similar, but much worse, problems trying to photograph CRT TVs,
as I found when drawing up the following web-pages on my site. Although
I haven't illustrated it there, most of the photos of the CRT taken in
preparation had to be junked because sections of the picture were very
dark and others very bright - it was rare that by luck the camera
captured one complete CRT scan acceptably evenly. Their primary purpose
was to compare the output of a CRT TV and a flat panel TV displaying the
same static picture, but wrt to the current thread title, by chance the
second page of the demo shows quite well the effect of the vertical
shadow-mask of the CRT, and the actual LEDs of the flat panel.

www.macfh.co.uk/JavaJive/AudioVisualTV/CRTvsLCD/CRTvsLCD-p1.html

What you haven't really mentioned, in fact I don't think anyone really
has in the thread, is the response of the human eye. Although on this
subject I have found contrary information on some sites that I would
normally consider to be reliable, my understanding remains as follows.

There are two types of photo-receptive cell in the human eye, rods and
cones (there is actually a third type responsive to photo-period, which
is not relevant here), with the former being sensitive to blue light and
the latter being further split into two more types being sensitive to
red and green light respectively; evolutionarily speaking, the
differentiation between red and green came last. The above explains why
we are able to mimic so much of the world that we see by using three
primary colours, the additive primaries above, or their corresponding
subtractive primaries yellow (white without blue), magenta (ditto
green), and cyan (ditto red).

A point often overlooked is that the cones are less sensitive than the
rods, hence, as dusk falls, our seeing of red and green starts to fail
before our seeing of blue, resulting in what the French expressively
call "L'Heure Bleu", "The Blue Hour", around dusk. However, this also
affects the colours we see under sodium street lighting, because of the
faintness of the other colours in sodium's spectrum.

You should be able to demonstrate this relative sensitivity to
yourselves with the following picture. Print it out and leave it on a
window sill where there is no artificial light as dusk begins to fall.
You should observe that to begin with the red and perhaps the green
appear brighter than the blue, but as the daylight fades there'll come a
point where the blue should appear brighter than the other two colours.
At this point, the cones are failing, but the rods are still working.

www.macfh.co.uk/Temp/RedGreenBlue.png

For completeness, there is also a subtractive primary version of the
above, but I don't recall ever trying to see what happens to this as
dusk falls!

www.macfh.co.uk/Temp/CyanMagentaYellow.png

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

Re: What shape are pixels?

<t1d53b$p1e$1@dont-email.me>

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Subject: Re: What shape are pixels?
Date: Tue, 22 Mar 2022 18:38:11 -0000
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 by: NY - Tue, 22 Mar 2022 18:38 UTC

"Java Jive" <java@evij.com.invalid> wrote in message
news:t1cmph$u4e$1@dont-email.me...
> On 22/03/2022 09:52, NY wrote:
>>
>> "Brian Gaff (Sofa)" <briang1@blueyonder.co.uk> wrote in message
>> news:t1bvk0$l4s$1@dont-email.me...
>>>
>>> I do remember its all to do with colour temperature and lumins,
>>> something I never bothered about when I could see. All I remember was
>>> early LEDs that looked white to the naked eye seemed to look bluish when
>>> they were used daylight around and that most fluorescent tubes looked
>>> dotty or yellow. If you shot pictures with a video in such environments,
>>> the latter turned everyone's faces green unless you changed the tint on
>>> the camera, and the former looked a bit like blue light shown through
>>> mud is the best way I can describe it. It does show up how clever the
>>> eye and brain are when they work correctly to getting the colours to
>>> look right, wheas electronic devices show what is really there.
>>> I remember taking non flash photos under those orange street lights with
>>> some very alien looking results. Some cars almost shone, yet others were
>>> really black even when blue.
>>> Some headlights were greeny yellow,while others were just whitish.
>>
>> Any lights with discontinuous spectrums (as opposed to "black body
>> radiation", as taught in physics A level) will appear differently
>> depending on the ways the RGB sensors respond to light.
>
> Yes, while the sodium street lights that Brian refers to are predominantly
> yellow, because the spectrum of sodium has a pair of very bright yellow
> lines, in fact there are other colours in there as well - although it's
> long time since I looked at the spectrum of one of those lamps as part of
> a lab experiment, I remember some fainter red and green lines as well.
> [Searches] Yes, lovely photo of the spectrum here, though I'm not sure
> why the areas between the radiation lines aren't black as they were in the
> experiment that I ran:

Also there are two types of sodium lights. Low pressure ones are the sort
that were used for street lights and were truly horrible as a light source
because they are virtually monochromatic and so don't give any perception of
colour. But there are also high-pressure ones which give a peach-coloured
light with a bit of colour perception because they have a broader spectrum -
ie a greater spread of discrete lines.

>> https://i.postimg.cc/c4TW1zT4/daylight.jpg
>> https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
>> https://i.postimg.cc/NfQYct6z/Led.jpg
>> https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
>> https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg
>
> Interesting. Only the last of those looks truly awful. However, can I
> offer some advice? Next time use a tripod to ensure that the setup of
> each shot is identical. As you suggest most photo/scanning equipment uses
> correction technologies of some sort, even if it's only as unsophisticated
> as 'integrate to grey' in a film-era photo lab's printing machine, and
> therefore, theoretically at least, varying the composition might alter any
> auto-corrections applied by the equipment used, and hence the result not
> be a comparison only of the light source used, though I admit that such is
> not apparent in the shots you have linked.

I had to take the photos in a variety of locations, depending on where there
was a lamp of the desired type. In all cases I white-balanced off a piece of
paper which completely filled the frame, so the camera would only "see"
white of the appropriate colour. There may be slight differences in
exposure, though I tried to make sure the test image filled almost the whole
frame. I should have stuck the loose objects (box of screws and box of
drills) to the background image so they were in identical locations for all
shots and ensured all the images were framed identically.

>> One of the things you need to be careful of with LEDs is that they are
>> pulsed at high frequency with a mark:space ratio which varies as you dim
>> the light. This can lead to horizontal bands on photos if the camera
>> sensor reads the brightness of each row of pixels in turn, and the LEDs
>> were on for some rows and off for others. I presume when LEDs are used to
>> illuminate a TV studio they are driven from DC, with control over the
>> current to dim the light, so they do not turn on and off.
>
> You get similar, but much worse, problems trying to photograph CRT TVs, as
> I found when drawing up the following web-pages on my site. Although I
> haven't illustrated it there, most of the photos of the CRT taken in
> preparation had to be junked because sections of the picture were very
> dark and others very bright - it was rare that by luck the camera
> captured one complete CRT scan acceptably evenly. Their primary purpose
> was to compare the output of a CRT TV and a flat panel TV displaying the
> same static picture, but wrt to the current thread title, by chance the
> second page of the demo shows quite well the effect of the vertical
> shadow-mask of the CRT, and the actual LEDs of the flat panel.

The best way to photograph a TV screen apparently is to use a small aperture
and/or a neutral density filter to make the exposure several seconds, so the
difference between n and n+1 scans in different parts of the frame is
minimal because n is large. Obviously this only works with a still image on
the TV screen ;-) ND filter is probably a better way because most lenses
have an optimum aperture: too large (small f number) and parts of the screen
may be out of focus when the centre is in focus, but too small an aperture
may introduce diffraction effects.

> www.macfh.co.uk/JavaJive/AudioVisualTV/CRTvsLCD/CRTvsLCD-p1.html

An interesting comparison.

The other problem that you might encounter is moiré: a wavy-line pattern
which is "beating" between the pixel spacing in the source image and that in
the photo of the screen, though perhaps it is less so when the pixels of the
source image are so much larger than the pixels of your photos of the
screen.

It would be interesting to compare those photos with the original image, if
you can grab it electronically and scale it the same as the photos of the
screen.

> What you haven't really mentioned, in fact I don't think anyone really has
> in the thread, is the response of the human eye. Although on this subject
> I have found contrary information on some sites that I would normally
> consider to be reliable, my understanding remains as follows.
>
> There are two types of photo-receptive cell in the human eye, rods and
> cones (there is actually a third type responsive to photo-period, which is
> not relevant here), with the former being sensitive to blue light and the
> latter being further split into two more types being sensitive to red and
> green light respectively; evolutionarily speaking, the differentiation
> between red and green came last. The above explains why we are able to
> mimic so much of the world that we see by using three primary colours, the
> additive primaries above, or their corresponding subtractive primaries
> yellow (white without blue), magenta (ditto green), and cyan (ditto red).
>
> A point often overlooked is that the cones are less sensitive than the
> rods, hence, as dusk falls, our seeing of red and green starts to fail
> before our seeing of blue, resulting in what the French expressively call
> "L'Heure Bleu", "The Blue Hour", around dusk. However, this also affects
> the colours we see under sodium street lighting, because of the faintness
> of the other colours in sodium's spectrum.
>
> You should be able to demonstrate this relative sensitivity to yourselves
> with the following picture. Print it out and leave it on a window sill
> where there is no artificial light as dusk begins to fall. You should
> observe that to begin with the red and perhaps the green appear brighter
> than the blue, but as the daylight fades there'll come a point where the
> blue should appear brighter than the other two colours. At this point, the
> cones are failing, but the rods are still working.
>
> www.macfh.co.uk/Temp/RedGreenBlue.png
>
> For completeness, there is also a subtractive primary version of the
> above, but I don't recall ever trying to see what happens to this as dusk
> falls!
>
> www.macfh.co.uk/Temp/CyanMagentaYellow.png

Amazing what facts the brain retains without you knowing. As soon as I read
your description, the term "Purkinje effect" spring into my brain. I didn't
know that I knew about this...

Re: What shape are pixels?

<j9vfsgF9t05U1@mid.individual.net>

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From: wrightsa...@f2s.com (williamwright)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
Date: Wed, 23 Mar 2022 02:44:31 +0000
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 by: williamwright - Wed, 23 Mar 2022 02:44 UTC

On 22/03/2022 09:52, NY wrote:
> https://i.postimg.cc/c4TW1zT4/daylight.jpg
> https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
> https://i.postimg.cc/NfQYct6z/Led.jpg
> https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
> https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg

You should have equalised the exposures and gamma in order to make a
comparison.

Bill

Re: What shape are pixels?

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From: rjf...@escapetime.myzen.co.uk (Roderick Stewart)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
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 by: Roderick Stewart - Wed, 23 Mar 2022 09:50 UTC

On Tue, 22 Mar 2022 18:38:11 -0000, "NY" <me@privacy.invalid> wrote:

>The best way to photograph a TV screen apparently is to use a small aperture
>and/or a neutral density filter to make the exposure several seconds, so the
>difference between n and n+1 scans in different parts of the frame is
>minimal because n is large.

Once I worked in a university audiovisual department, where we would
occasionally be asked - sometimes by professors or other clever people
with letters after their names - if when photographing a TV screen it
was best to have the camera's flash switched on or off.

Apparently it's possible to live in the real world but not pay much
attention to it.

Rod.

Re: What shape are pixels?

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From: rjf...@escapetime.myzen.co.uk (Roderick Stewart)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
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 by: Roderick Stewart - Wed, 23 Mar 2022 10:01 UTC

On Wed, 23 Mar 2022 02:44:31 +0000, williamwright
<wrightsaerials@f2s.com> wrote:

>On 22/03/2022 09:52, NY wrote:
>> https://i.postimg.cc/c4TW1zT4/daylight.jpg
>> https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
>> https://i.postimg.cc/NfQYct6z/Led.jpg
>> https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
>> https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg
>
>You should have equalised the exposures and gamma in order to make a
>comparison.
>
>Bill

Maybe also use a variety of natural test subjects covering the full
visible spectrum. A photograph in a printed magazine has already been
analysed by a filter system and then displayed using only three
artificial pigments.

Rod.

Re: What shape are pixels?

<59cda0a746charles@candehope.me.uk>

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From: char...@candehope.me.uk (charles)
Subject: Re: What shape are pixels?
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 by: charles - Wed, 23 Mar 2022 10:17 UTC

In article <52rl3hldbj798157dtecv8mqqum3kq25o3@4ax.com>,
Roderick Stewart <rjfs@escapetime.myzen.co.uk> wrote:
> On Tue, 22 Mar 2022 18:38:11 -0000, "NY" <me@privacy.invalid> wrote:

> >The best way to photograph a TV screen apparently is to use a small
> >aperture and/or a neutral density filter to make the exposure several
> >seconds, so the difference between n and n+1 scans in different parts
> >of the frame is minimal because n is large.

> Once I worked in a university audiovisual department, where we would
> occasionally be asked - sometimes by professors or other clever people
> with letters after their names - if when photographing a TV screen it
> was best to have the camera's flash switched on or off.

> Apparently it's possible to live in the real world but not pay much
> attention to it.

> Rod.

Back in the 1970s, I was showing off Ceefax at the TV exhibition in
Montreaux. Someone wanted a picture of the screen, held up his light meter,
remarked that it was quite low levle, so turned on his flash. I wonder
what he though when thefilm came back from the lab.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Re: What shape are pixels?

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From: wrightsa...@f2s.com (williamwright)
Newsgroups: uk.tech.digital-tv
Subject: Re: What shape are pixels?
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 by: williamwright - Wed, 23 Mar 2022 10:58 UTC

On 23/03/2022 10:17, charles wrote:
> Back in the 1970s, I was showing off Ceefax at the TV exhibition in
> Montreaux. Someone wanted a picture of the screen, held up his light meter,
> remarked that it was quite low levle, so turned on his flash. I wonder
> what he though when thefilm came back from the lab.

He'd think the telly was faulty.

Bill

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
Date: Wed, 23 Mar 2022 11:12:12 -0000
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 by: NY - Wed, 23 Mar 2022 11:12 UTC

"Roderick Stewart" <rjfs@escapetime.myzen.co.uk> wrote in message
news:ccrl3htbgpj1lje0ru67fbmjkb9r8t5u7n@4ax.com...
> On Wed, 23 Mar 2022 02:44:31 +0000, williamwright
> <wrightsaerials@f2s.com> wrote:
>
>>On 22/03/2022 09:52, NY wrote:
>>> https://i.postimg.cc/c4TW1zT4/daylight.jpg
>>> https://i.postimg.cc/HLrdhtwW/daylight-CFL.jpg
>>> https://i.postimg.cc/NfQYct6z/Led.jpg
>>> https://i.postimg.cc/1RGP2XqF/white-fluor.jpg
>>> https://i.postimg.cc/br9htVhg/white-fluor-daylight-WB.jpg
>>
>>You should have equalised the exposures and gamma in order to make a
>>comparison.
>>
>>Bill
>
> Maybe also use a variety of natural test subjects covering the full
> visible spectrum. A photograph in a printed magazine has already been
> analysed by a filter system and then displayed using only three
> artificial pigments.

All good suggestions. I was limited in my choice of test subject by needing
something which could be moved to the locations where the lights were. The
only fluorescent tubes we had were lights in the loft, and the only LED
lights were GU10s in the bathroom ceiling. I remember having to hold the
camera at a slight angle to the printed page for the LED photo to avoid
picking up a reflection of the light in the shiny paper. The photos I posted
are smaller versions of the originals, and this means the exposure details
have not been preserved, but I remember choosing long exposures for the
artificial lights to avoid any appreciable difference due to persistence of
phosphors on fluorescent and LED: an exposure of (for example) 1/80 second
would only catch *part* of a mains cycle and so there could be a greater
dominance of the discharge (blueish) of a fluorescent and less of the
phosphor (yellowish). So I was thinking of minimising *some* differences ;-)

If I was doing the test now I would choose a subject that had a full range
of colours of real-world objects (not restricting to a printed photo subject
to CMYK inks). And I'd mark the subject so I knew exactly how to adjust
camera position (framing, distance from subject) to get identical framing in
all photos which would allow the camera's auto exposure to correct for the
great differences in light levels between one lights source and another -
for example, bright sunlight would be many many times brighter than
artificial lights. Maybe I'd also find somewhere shady outdoors (but free of
colour cast reflected from walls, trees etc) to test shade (which is about
10,000 K, as opposed to about 5500 K for direct sunlight). And maybe try
various different LED bulbs: we have two types in our kitchen which are both
sold as "daylight" but one is slightly more yellow and less blue than the
other (to the naked eye). And maybe even try Philips Hue (which allow RGB
levels to be adjusted) on various standard presets.

One thing that I'd need to consider: some objects fluoresce slightly under
UV light which might be present in direct sunlight, though whether that
would be noticeable in relation to the incident sunlight is very doubtful
;-)

I remember once testing tungsten bulbs on various settings of a thyristor
dimmer: as well as the brightness varying, the colour temperature decreases
(light becomes more yellow/orange) as you dim. I can't find the photos, but
I seem to remember that the photos I took showed remarkably little
difference once the camera had auto-adjusted the white balance as well as
the exposure. But then that is a black-body source with a continuous
spectrum, whereas fluorescent and LED have discontinuities.

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
Date: Wed, 23 Mar 2022 11:29:54 -0000
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 by: NY - Wed, 23 Mar 2022 11:29 UTC

"williamwright" <wrightsaerials@f2s.com> wrote in message
news:ja0cqbFf5ciU1@mid.individual.net...
> On 23/03/2022 10:17, charles wrote:
>> Back in the 1970s, I was showing off Ceefax at the TV exhibition in
>> Montreaux. Someone wanted a picture of the screen, held up his light
>> meter,
>> remarked that it was quite low levle, so turned on his flash. I wonder
>> what he though when thefilm came back from the lab.
>
> He'd think the telly was faulty.

One of the problems with photographing TV or computer screens in a general
view of an office etc is to get the exposure of the image and of the office
sufficiently similar that the screen is not burnt-out. Screens are usually
mid-grey when they are off, so the image on the screen is usually set to be
bright enough that a full range of tones is visible, without all the darker
tones being lost in the grey ambient reflection.

When shooting by flash, there are several variables that need to be juggled:

- shutter speed of maybe half a second to minimise difference between
different parts of the screen getting n or n+1 scans

- shutter speed definitely low enough (< 1/125 second) that flash will
synchronise (but the first point takes care of that)

- take a light reading off the screen (with the room lighting low) to
determine correct aperture

- set flash power so it is correct for the chosen aperture; probably bounce
the flash off a white ceiling or at least a card to give softer light than
direct flash, and to lessen any reflection of the flash in the screen.

Apparently when CRTs were included in vision for a film camera or a TV
camera, the camera was synchronised with the video sync to avoid a rolling
bar on the screen image: maybe even run the camera without film, checking
for a visible bar in the viewfinder and adjusting phase to move it
off-screen.

Beating can be a problem between 50 Hz video rate, and 60 Hz or 75 or 90 or
120 or whatever for computer image. When I was filming a short video at work
once with a UK video camera, I adjusted the in-vision computer so it used a
50 Hz (or may 100 Hz) refresh rate to minimise rolling bars. I also turned
the screen brightness down to a level which was a strain on the eye to use,
so as to reduce the difference in screen and general scene brightness.

Re: What shape are pixels?

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 by: Max Demian - Wed, 23 Mar 2022 11:55 UTC

On 23/03/2022 09:50, Roderick Stewart wrote:
> On Tue, 22 Mar 2022 18:38:11 -0000, "NY" <me@privacy.invalid> wrote:
>
>> The best way to photograph a TV screen apparently is to use a small aperture
>> and/or a neutral density filter to make the exposure several seconds, so the
>> difference between n and n+1 scans in different parts of the frame is
>> minimal because n is large.
>
> Once I worked in a university audiovisual department, where we would
> occasionally be asked - sometimes by professors or other clever people
> with letters after their names - if when photographing a TV screen it
> was best to have the camera's flash switched on or off.
>
> Apparently it's possible to live in the real world but not pay much
> attention to it.

It's not immediately obvious which displays work by reflection and which
by producing light. LCDs work by reflection, but what if it relies on a
backlight? There are shopping coupons which are scanned by a laser in
the shop, but, if you don't have access to a printer, you are supposed
to be able to scan the bar/QR code on a smartphone screen; how does that
work? What if the display is OLED?

--
Max Demian

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
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 by: NY - Wed, 23 Mar 2022 12:32 UTC

"Java Jive" <java@evij.com.invalid> wrote in message
news:t1evn6$gkk$1@dont-email.me...
>> The other problem that you might encounter is moiré: a wavy-line pattern
>> which is "beating" between the pixel spacing in the source image and that
>> in the photo of the screen, though perhaps it is less so when the pixels
>> of the source image are so much larger than the pixels of your photos of
>> the screen.
>
> Yes, I've seen that often, particularly in JPGs, and also in scans of 120
> film negatives that were too big to fit in the neg holder of my scanner,
> so had to be laid flat on the glass, and actually weren't quite completely
> flat, resulting in what I call Moiré, others call Newton's rings. I still
> have about 20-30 of these latter that gave this problem, even under glass,
> and that I hope to rescan with a better quality result one day.

Ah! The dreaded Newton's Rings. I encountered that the other day when I was
scanning some 35 mm slides of my parents' wedding for their 60th
anniversary. Some of the slides had been mounted in glass-covered mounts and
the Newton's Rings were horrible. The glass was also dirty: it was easy to
clean the outside, but the inside looked to be mucky as well. I decided to
take those mounts apart (I was afraid of the plastic of the mount having
gone brittle after 60 years) and remount them temporarily in a spare mount
that I had. There was a very noticeable difference in quality due to there
being less (dirty) glass in the way, and no Newton's rings. I took the
opportunity to clean both side of both pieces of glass before remounting the
film in the glass frames after scanning.

When I had to enlarge from some of my dad's 120 negs many years ago I had
the same problem as you with not having a 120 neg frame. I used a sheet of
glass that I cleaned well and then sat on top of the neg on thin shims (I
think I used a couple of bits of fogged film from the beginning of a film)
so the neg didn't touch the glass. With a flatbed scanner as opposed to
printing onto paper, you can turn the film upside down to compensate for
direction of film curl when avoiding the film touching the glass and causing
Newton's rings, and then correct for the mirror-image in the computer.

My scanner tends to produce better results (better tonal range) if I scan as
a positive and correct in software, rather than scan as a (B&W) negative.
But negs in general (and especially colour ones) are a lot more difficult to
get good scans from than positive slides. The software corrects find for the
orange cast of a colour neg, but I get a lot of ghosting around dark objects
against a bright sky (ie object is bright and sky is dark on the neg) and
horrendous amoeba-like grain. That's both with a flatbed scanner and a
dedicated film scanner, and VueScan software because the Minolta software
doesn't install on Win 7 or 10. Results vary from really abominable to
fantastic, depending on film type. It probably doesn't help that standard
Kodak colour negatives types didn't seem to be in the software's presets,
either by name (Kodacolor) or code on the film's edge-marking. At best I got
considerably more detail in shadows and highlights than scanning from a
processing-shop print, but some photos had a weird effect like you got in
"colour plates" in books from the 1940s and 50s: colours too strong and
contrast too flat - all about larger-than-life - and standard saturation,
contrast and gamma controls in software didn't really correct for it.
Slides, other the other hand, required very little tweaking unless they were
vastly under- or over-exposed. I was impressed with how much I managed to
correct for some Ektachrome slides that I'd shot many years ago of
illuminated buildings at night, and I'd guessed the exposure wrong by about
3 stops overexposed. I was able to resolve enough highlight detail to
improve things quite a bit.

As an aside, I discovered a nasty problem with my film scanner when I was
scanning the wedding slides. My scanner has a shaft that advances the slide
past the sensor at a known rate, and this shaft is connected by a plastic
collar to a stepper motor. And over the years, that collar has split and so
sometimes was slipping. After getting several scan that were long and thin,
I managed a repair: wrap a bit of 3M magic tape (not conventional Sellotape
which has glue that oozes!) around the motor shaft to make it a bit bigger
diameter and then refit the split collar. Problem solved! I'd forgotten just
how slow my film scanner is when I'm doing multiple-reading scans, with
grain reduction, to minimise both grain and sensor noise. It was worth the
hassle, though. Thankfully all the slides I chose seem to have been
something over than Kodachrome so the IR dirt-reduction algorithm worked OK
(unlike Agfa and Kodak Ektachrome, Kodachrome has an emulsion which is not
uniformly transparent to IR, so the algorithm which uses IR to look for dirt
and dust on the film doesn't work because it sees darker parts of the image
as dirt).

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
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 by: NY - Wed, 23 Mar 2022 12:37 UTC

"Max Demian" <max_demian@bigfoot.com> wrote in message
news:E82dnS-guvgpl6b_nZ2dnUU7-c3NnZ2d@brightview.co.uk...
> It's not immediately obvious which displays work by reflection and which
> by producing light. LCDs work by reflection, but what if it relies on a
> backlight? There are shopping coupons which are scanned by a laser in the
> shop, but, if you don't have access to a printer, you are supposed to be
> able to scan the bar/QR code on a smartphone screen; how does that work?
> What if the display is OLED?

Like you, I've always wondered how laser barcode scanners manage to scan a
backlit LED screen rather than a reflective paper coupon (or an LCD screen).
Scanners in shops seem to have a switchable setting which maybe turns the
laser off and moves the sensor (or relies on movement of the phone screen
past the scanner) to sense the horizontal axis of the bar code.

Re: What shape are pixels?

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Subject: Re: What shape are pixels?
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In-Reply-To: <59cda0a746charles@candehope.me.uk>
 by: Mark Carver - Wed, 23 Mar 2022 13:16 UTC

On 23/03/2022 10:17, charles wrote:
>
> Back in the 1970s, I was showing off Ceefax at the TV exhibition in
> Montreaux.
Crystal Palace had one hell of a range !

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