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Author Topic: Is it possible to have a Prophoto RGB monitor  (Read 15153 times)
bharatbuysell
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« Reply #40 on: January 16, 2012, 12:59:57 AM »
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this topic is quite interesting  Smiley Smiley
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Ernst Dinkla
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« Reply #41 on: January 16, 2012, 02:13:33 AM »
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Another interesting approach is a CMYK monitor like possible with electrowetting displays. Liquavista>Samsung is developing that technology but it has been quiet  there the last year and a CMYK monitor must have the lowest priority of all. I do not know what a transmissive CMYK display could achieve in gamut with its subtractive color mixing but I suppose a 5 to 6 primaries OLED would make a wider gamut possible.

One thing will not change: the trend in gamut size increases and related bit depths applies to all components; camera sensors, image editors, printer output and monitors. Soft proofing will have a place as long as there are differences in size and shape of the gamuts used in the workflow. Given progress and changes in technology and the budgets to purchase equipment there probably will never be stable situations on amateur desktops and in pro studios over long periods so soft proof features should be improved first.

met vriendelijke groeten, Ernst
330+ paper white spectral plots:
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm





« Last Edit: January 16, 2012, 06:34:12 AM by Ernst Dinkla » Logged
hjulenissen
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« Reply #42 on: January 16, 2012, 03:33:37 AM »
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No, since two of the primaries (green and blue) are not physically realizable.

Just so that I am getting things here:
Is the fundamental problem that no three spectra can be designed that can excite the L, M and S cones independently? Even monochromatic ones that are placed at the wavelength extremes, and at zero-crossings?

What are the arguments for choosing broad, smooth PSD in display devices? To maximize energy efficiency? To minimize individual deviations from the CIE models?

If one could make a device that could generate any spectra with very narrow wavelength sampling, then any physical stimuli pertaining to the perceptual correlate "color" could be generated, right? If it cannot be generated physically (in nature or in the lab), then it probably is not a "color" we need to worry about?

-h
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acgoris
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« Reply #43 on: January 16, 2012, 10:06:32 AM »
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Q:  Is the fundamental problem that no three spectra can be designed that can excite the L, M and S cones independently?
A: Exactly

Q: Even monochromatic ones that are placed at the wavelength extremes, and at zero-crossings?
A: Correct

Q: What are the arguments for choosing broad, smooth PSD in display devices?
A:  They don't.  They usually try to make them as narrow as possible, which moves the primaries to the edges of the CIE diagram.  When you plot the CIE coordinates of the 3 primaries, you can reproduce any color inside that triangle. 

Q:  To maximize energy efficiency?
A:  This is definitely a consideration, especially when using a white backlight.  Any light that doesn't make it through a color filter is wasted energy.

Q: To minimize individual deviations from the CIE models?
A:  Variation from display to display, or within a display over time is an issue, and why we calibrate displays.  Display designers have to tradeoff several things - cost, brightness, size of gamut, reliability, consistency, etc.  Phosphors (used in CRT's and two common backlights for LCD panels - white LEDs and CCF tubes) shift color as they warm up, and as they age.   Some high-end wide-gamut LCD panels use RGB LEDs as their backlight.  These also shift color with temperature and age.   They also shift color with the amount of current flowing through them.   All of these shifts are small, but enough that professionals in the photography business care.

Q: If one could make a device that could generate any spectra with very narrow wavelength sampling, then any physical stimuli pertaining to the perceptual correlate "color" could be generated, right?
A:  Yes!  You just described the Holy Grail.   This has been done for film photography using an interference technique.  A extremely fine-grain film is required.  The pioneer of this was Gabriel Lippmann, who won the Nobel prize in 1908 for his work.  Wikipedia has a good description of how this works if you look up Gabriel Lippmann.

Q: If it cannot be generated physically (in nature or in the lab), then it probably is not a "color" we need to worry about?
A: Correct!   You could even change the word "probably" to "definitely" :-). 



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hjulenissen
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« Reply #44 on: January 16, 2012, 12:07:12 PM »
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Q:  To maximize energy efficiency?
A:  This is definitely a consideration, especially when using a white backlight.  Any light that doesn't make it through a color filter is wasted energy.
I have seen suggestions that "wide gamut" displays actually tend to have regular spectral selectivity in the lcd panel, while the "white" backlight is more like 3 narrow peaks centered at "L", "M" and "S" in such a ratio that it is perceived as white.
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Q: To minimize individual deviations from the CIE models?
A:  Variation from display to display, or within a display over time is an issue, and why we calibrate displays.  Display designers have to tradeoff several things - cost, brightness, size of gamut, reliability, consistency, etc.  Phosphors (used in CRT's and two common backlights for LCD panels - white LEDs and CCF tubes) shift color as they warm up, and as they age.   Some high-end wide-gamut LCD panels use RGB LEDs as their backlight.  These also shift color with temperature and age.   They also shift color with the amount of current flowing through them.   All of these shifts are small, but enough that professionals in the photography business care.
Actually, my thought was that the actual perception of color for an individual could deviate somewhat from the standardised CIE response. If this is the case, it would make sense to use display PDFs that minimized person-to-person variability. Without proof, it seems sensible to me that smooth, regular PSDs would tend to be less sensitive to variation than monochromatic light at the wavelength extremes.
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Q: If one could make a device that could generate any spectra with very narrow wavelength sampling, then any physical stimuli pertaining to the perceptual correlate "color" could be generated, right?
A:  Yes!  You just described the Holy Grail.   This has been done for film photography using an interference technique.  A extremely fine-grain film is required.  The pioneer of this was Gabriel Lippmann, who won the Nobel prize in 1908 for his work.  Wikipedia has a good description of how this works if you look up Gabriel Lippmann.
A DLP-type projector with e.g. 256 narrow-band filters in its color wheel operating at 256x the desired framerate/rainbow-flicker threshold at 256x the normal brightness fed a HDMI input at 256/3 times the regular bandwidth should work. I have no idea how hard it is to manufacture such filters.

.h
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acgoris
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« Reply #45 on: January 16, 2012, 06:16:09 PM »
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As far as filters for your hyperspectral DLP projector, yes they are readily available.   Image Engineering uses filters like this in their camSPECS camera calibrators.

256 bands might be overkill, but I would still like to view an implementation of this concept.   If you're going this far, rather than have a bunch of filters, I'd just build a super-bright super-fast sweeping monochrometer (uses a diffraction grating and white light to make any wavelength you want).  As far as human perception, there will be diminishing returns as one goes from 3 primaries to 4 primaries (like Sharp's Quattron display with RGBY) and beyond.   If the goal is a tool for research into human vision and rendering, then the more the better.  I would think you'd be doing pretty good with 30 bands (10-12nm spacing), but you'd need more if you wanted to truly simulate fluorescent lights.  It would be nice to have pixels in the near IR and near UV as well.  Young children can see much further into the UV than adults.  People who've had cataract surgery and opted for non-UV blocking lenses (a friend of mine recently did this) can see to the mid-300nm's.

Here's my gut feel for the number of bands that would be be good for different applications (I'm interested in other folks opinions on this)  There is diminishing returns in all of these, and keep in mind that for most applications, existing wide gamut 3-primary displays work really well, if calibrated correctly and used correctly in a color-managed workflow.

More accuracy in soft-proofing prints: 4-6 primaries
Covering PhotoRGB:  5 primaries
Reproducing highly-vivid objects, like neon lights (Neon Tunnel at O'Hare Airport), bird feathers (Peacock, Scarlet Tanager, Scarlet Macaw, Kingfisher, Painted Bunting), butterflies (Emerald Swallowtail, Blue Morpho), certain specialty paints (including fluorescent paints): 5-7 primaries
Color Vision Research:  50-200 primaries (or 'bands') that extend from 350nm to 750nm

If you divvied the primaries up across multiple DLPs and had them all point at the same screen, you could build a hyperspectral display without the temporal artifacts in time-multiplexed color displays.  The latter happens as your eye moves across the screen as it refreshes each color.  If you have a white line on a black background, you'll see a nice rainbow.  It is fatiquing, even in 180Hz displays (60Hz/color in a 3-color system) showing a friendly (non-pathological case) picture.
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WombatHorror
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« Reply #46 on: January 17, 2012, 06:41:03 PM »
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For the 6th primary, I'd consider a white pixel.   Here's why:  When you synthesize a color in the middle of the CIE diagram with a green primary and  two nearly-monochromatic primaries out near the lower corners of the CIE diagram, it is possible to sense chromatic aberration in the corners if you wear glasses.   I noticed this effect on a LaCie wide gamut monitor.   Here's the experiment:  fill the screen with white text on a black background.  Sit reasonably close to the monitor (typical 18" viewing distance) and look at the text in the center of the screen.  Without moving your head, sense the text in the corners of the screen, and you can see the split of the red and blue channels.   I wear low-dispersion glasses, but easily saw a 1 to 1.5 pixel split between the red and blue signals making up the white characters on the LaCie monitor in the corner.  If I turn my head and look directly at the character the effect immediately goes away.   

Why would a white primary help this any? It would be spitting out a mix of photons at different frequencies and why would they suddenly all go through glasses without any dispersion?

 
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acgoris
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« Reply #47 on: January 17, 2012, 09:50:11 PM »
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Q:  Why would a white primary help this any? It would be spitting out a mix of photons at different frequencies and why would they suddenly all go through glasses without any dispersion?

A:  Good question.  Here was my thinking:  First, I agree the components of white light would disperse just like monochromatic primaries do.  However, when you have a wide mix of wavelengths (assuming the white has a broad, somewhat smooth spectrum...I should have been specific), a fewer percentage of it's photons are out at the wavelength extremes, and so the dispersion of these outer wavelengths might not be as noticeable.  If the white contains some red at 700nm, that red component will disperse the same as a monochromatic red primary at 700nm, which I think is your point.  However, the number of photons at 700nm emitted by a broad-spectrum white LED would be less than the number of photons emitted at 700nm by a monochromatic 700nm LED used as part of an RGB synthesis of white.  Similar situation for blue. 

Any benefit of a white LED would have to be tested against the benefit of another monochromatic primary, and the benefits of another monochromatic primary would probably win.  The general question could be posed as this:  In a display with more than 3 primaries, but less than many (8? 10?), is there any benefit to having one or more of those primaries being broad-spectrumed?   With 3 or 4 primaries, obviously not.  With many primaries, obviously not.
 
Thoughts?

To address another persons question about human-to-human variability....if you push the bluest primary very far towards 400nm, it may effect older viewers experiencing age-related change in sensitivity to shorter wavelengths due to yellowing of the lens.   I recently did some testing of this cutoff using a monochrometer with some colleagues and myself, and alas my 55-year old eyes don't detect 400nm, although my resolution is tac-sharp.  So I'm yellow but not fuzzy.
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WombatHorror
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« Reply #48 on: January 17, 2012, 11:16:54 PM »
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Q:  Why would a white primary help this any? It would be spitting out a mix of photons at different frequencies and why would they suddenly all go through glasses without any dispersion?

A:  Good question.  Here was my thinking:  First, I agree the components of white light would disperse just like monochromatic primaries do.  However, when you have a wide mix of wavelengths (assuming the white has a broad, somewhat smooth spectrum...I should have been specific), a fewer percentage of it's photons are out at the wavelength extremes, and so the dispersion of these outer wavelengths might not be as noticeable.  If the white contains some red at 700nm, that red component will disperse the same as a monochromatic red primary at 700nm, which I think is your point.  However, the number of photons at 700nm emitted by a broad-spectrum white LED would be less than the number of photons emitted at 700nm by a monochromatic 700nm LED used as part of an RGB synthesis of white.  Similar situation for blue. 

I wonder though,if it didn't have enough energy near the ends as the middle would it not appear tinted?

OTOH with the complex response of the cones maybe a white could be mixed from energies not as far apart as the traditional red and blue primaries have most of their high energy spectral spiked at. Not sure what white LEDS output and how readily you can tune ones that work well. Maybe assumign a suitable LED can be made you could at least reduce it slightly.

Quote
To address another persons question about human-to-human variability....if you push the bluest primary very far towards 400nm, it may effect older viewers experiencing age-related change in sensitivity to shorter wavelengths due to yellowing of the lens.   I recently did some testing of this cutoff using a monochrometer with some colleagues and myself, and alas my 55-year old eyes don't detect 400nm, although my resolution is tac-sharp.  So I'm yellow but not fuzzy.

I just read that while the average person has a 2:1 ratio of M to L cones that they recentlyish discovered tremendous variation from person to person with some having a 1:1 ratio and others having as high as a 17:1 ratio.
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Pictus
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« Reply #49 on: January 18, 2012, 01:31:15 PM »
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Only when the evolution of our species allows us to see outside the current visible electromagnetic spectrum. By then, we will not need displays, we will be closer the Arthur C. Clarks super embryos <g>

http://en.wikipedia.org/wiki/Talk%3ATetrachromacy  Grin
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hjulenissen
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« Reply #50 on: January 18, 2012, 01:58:51 PM »
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To address another persons question about human-to-human variability....if you push the bluest primary very far towards 400nm, it may effect older viewers experiencing age-related change in sensitivity to shorter wavelengths due to yellowing of the lens.   I recently did some testing of this cutoff using a monochrometer with some colleagues and myself, and alas my 55-year old eyes don't detect 400nm, although my resolution is tac-sharp.  So I'm yellow but not fuzzy.
Is the PSD (power spectral sensitivity?) of my "L", "M" and "S" cones smooth or irregular? Is it consistent from one part of my eye to the other? Is it consistent from me to the next guy?

If they are very smooth, one could essentially excite them using any narrow/irregular PSD that integrate to the desired power, or one at the wavelength extremes. One drawback of going for nearly invisible wavelength is that you might have to increase the total transmitted energy as the perceived sensitivity is so low.

If the perception spectral response and the transmission of some display are both highly irregular, even minor wavelength deviations could cause large changes in perceived "color". Then it would make a lot of sense to strive for smooth excitation PSDs?

-h
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WombatHorror
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« Reply #51 on: January 18, 2012, 03:43:32 PM »
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wiki is down today so I can't read that but I did read elsewhere yesterday how on a HDR displays if they tune down the white point they can get people to register color more intense than the white point was predicted to allow, or something like that, I think they were implying it could make people see colors beyond what was thought possible (under very special circumstances only though) although they may merely have meant colors not expected to be able to be shown given certain considerations which wouldn't be the same thing at all.
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WombatHorror
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« Reply #52 on: January 18, 2012, 03:46:41 PM »
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Is the PSD (power spectral sensitivity?) of my "L", "M" and "S" cones smooth or irregular? Is it consistent from one part of my eye to the other? Is it consistent from me to the next guy?

If they are very smooth, one could essentially excite them using any narrow/irregular PSD that integrate to the desired power, or one at the wavelength extremes. One drawback of going for nearly invisible wavelength is that you might have to increase the total transmitted energy as the perceived sensitivity is so low.

If the perception spectral response and the transmission of some display are both highly irregular, even minor wavelength deviations could cause large changes in perceived "color". Then it would make a lot of sense to strive for smooth excitation PSDs?

-h

I believe it's been found that for the average person there is nothing that can excite just each one alone no matter what you try to do and that the best case scenario when trying to excite L, M,S as much alone as possible actually does not use light extremes out toward the edges at all, I forget the numbers used but two of them were quite close I think and even the third not way out there.
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madmanchan
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« Reply #53 on: January 18, 2012, 05:00:30 PM »
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The human cone responses overlap so you can't stimulate one without stimulating another.  (Similar to cameras.)
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WombatHorror
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« Reply #54 on: January 18, 2012, 08:13:02 PM »
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Q:  Why would a white primary help this any? It would be spitting out a mix of photons at different frequencies and why would they suddenly all go through glasses without any dispersion?

A:  Good question.  Here was my thinking:  First, I agree the components of white light would disperse just like monochromatic primaries do.  However, when you have a wide mix of wavelengths (assuming the white has a broad, somewhat smooth spectrum...I should have been specific), a fewer percentage of it's photons are out at the wavelength extremes, and so the dispersion of these outer wavelengths might not be as noticeable.  If the white contains some red at 700nm, that red component will disperse the same as a monochromatic red primary at 700nm, which I think is your point.  However, the number of photons at 700nm emitted by a broad-spectrum white LED would be less than the number of photons emitted at 700nm by a monochromatic 700nm LED used as part of an RGB synthesis of white.  Similar situation for blue. 

Any benefit of a white LED would have to be tested against the benefit of another monochromatic primary, and the benefits of another monochromatic primary would probably win.  The general question could be posed as this:  In a display with more than 3 primaries, but less than many (8? 10?), is there any benefit to having one or more of those primaries being broad-spectrumed?   With 3 or 4 primaries, obviously not.  With many primaries, obviously not.
 
Thoughts?


yeah assuming you can make such a white LED you could surely have it excite the cones in a way to produce white using frequencies much more bunched together than the three primaries of most displays, especially compared to wider gamut ones. Of course there would still be some degree of dispersion and you'd still have some mix of the 3 primaries with full dispersion so it wouldn't come close to reducing it to zero by any means but to some extent I'm pretty sure it could help. But who knows if they can easily make such a white LED (I suppose they could break it into three monochrome subpixels though so hmm I guess it certianly should be doable). I'm not sure they care enough about the glasses wearers though to bother and how much the improvement would be and would it be worth it I don't know.

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