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Author Topic: TRC of the monitor vs gamma of the image in color aware applications  (Read 3271 times)
Krunoslav Stifter
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« on: January 13, 2013, 07:28:07 PM »
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Hi, guys

First time posting here, but been reading the forums for few weeks. Great community. Smiley

I'm creating tutorials on color management and I have one big question mark.

Part of the tutorials is about TRC (Tone Response Curve) and Gamma values of the monitor and of the images. So one is what everybody keeps talking about and that is that when you view in image in color managed application like Photoshop. It adjusts the gamma of the image independently of the gamma of the monitor. I agree with that, but what confuses me is what people are saying is that basically Photoshop reads the gamma from the image profile and one from monitor and compensates for any deviation of the monitor gamma from that of image gamma.

Let me list you some of the articles that made me ask this question.

ISO 12646: Monitor Calibration: Theory and Practice for the Fine Arts

"colour managed applications like Adobe Photoshop™ will automatically transform image data to the current monitor profile ensuring correct values are displayed on screen irrespective of the monitor’s gamma. The monitor’s gamma setting therefore only alters the appearance of non colour managed content and applications, and does not alter the monitor’s white or black points, only the relative brightness of the mid tones on screen. "

Spyder 3 Elite - Calibration Settings Help Manual

"Calibrating to the expected gamma and white point for the type of work you do can make non-color managed applications display in a more reasonable manner. Color managed applications will compensate for your choice of gamma, so choosing a gamma setting close to the display's native gamma minimizes lost levels and increases smoothness.

...Color managed applications adjust for monitor gamma, showing similar results at a range of gamma choices. Gamma 2.2 also provides a perceptually uniform tone range to the observer"

Source: http://dpbestflow.org/node/266

"Gamma is less important than white point and luminance for photographers because color managed image editing applications such as Photoshop automatically adjust for gamma and display all images the same, regardless of monitor gamma."



Photoshop and Your Monitor: Adapted from Real World Adobe Photoshop CS5 for Photographers (Peachpit Press) By Conrad Chavez

"Some beginners think they need to calibrate and profile a monitor to the same specs as the working space. That’s a mistake; the white point and gamma of your display are entirely independent of the white point and gamma of your working space. The color management system translates working space white point and gamma seamlessly to those of your display. The goal in setting white point and gamma for the display is simply to make the display behave as well as it can."

DigitalDog

"The Gamma (actually TRC) of the display and the working space do not have to match. They share the same term but this tone curve is being described by two different beasts. So no, you absolutely do not need to calibrate a display to a TRC that matches a working space."




I did my research and it theory I understand but in practice I'm not sure and I'm looking for confirmation.

What confuses me is that my native gamma of my monitor is 1.9, way of from the typical gamma of 2.2 that is used in images. I have calibrated to gamma 2.2 so the TRC is bend to darken the display and match the Gamma 2.2. and when I deactivate my calibration profile it goes back to what I presume is my native gamma of the monitor that is 1.9 and naturally everything becomes lighter in screen. To my eyes it seems that the image opened in Photoshop goes lighter as well along with all the UI elements. But it could be that my eyes are simply effected by the surrounding UI elements becoming lighter all of a sudden and maybe the image brightness dosent change. I can't be sure and I don't know how to confirm it.

What I understand by reading this articles is that they are basically saying - Photoshop adjusts the gamma of the image based on the gamma found n the profile of the image and also takes the profile of the monitor whatever it is in order to compensate and display image like is should be gamma 2.2

I am not sure about that since to my eyes it seems like when I deacitve my monitor profile made by Spyder calibrator - it switches the monitor to gamma 1.9 (native for my monitor) and to my eyes it seems like the image and the UI of Photoshop goes lighter as well, and that would mean that PS is in fact effected primarily by the gamma of the display. Can some of you more techno savy users please help me find out what is really going on. I would like to make a tutorial with accurate information.

Thank you for the help.
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Tim Lookingbill
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« Reply #1 on: January 13, 2013, 09:27:26 PM »
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http://www.cambridgeincolour.com/tutorials/monitor-calibration.htm

Images that are edited to look a desired way on a calibrated and profiled display rely on the gamma embedded in the tagged color space the original edits were encoded under so those edited images look the same across a wide range of displays regardless of brightness and color managed imaging app viewed in.

All displays must show the same evenly distributed black to white gradient (an objective target for determining linear response). Some display's native gamma will show this gradient as it should and measure around 2.2.

You might want to adjust your display's contrast and brightness buttons (hardware) to force your display to natively measure 2.2 so the video card LUT curves aren't distorted into forcing this response through software.

Color managed applications rely on the embedded gamma the image was edited in determined by the tagged profile. This gamma number may be 1.8=ProPhotoRGB or 2.2=AdobeRGB/sRGB.

When you change the gamma curve of your display profile the image viewed in Photoshop will lighten or darken not only from this display profile change but also whatever the gamma curve of the color space the image was edited in and that might have been on a very dark or very bright display which makes predicting and understanding this behavior unnecessary if not impossible.

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Krunoslav Stifter
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« Reply #2 on: January 13, 2013, 09:55:22 PM »
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You might want to adjust your display's contrast and brightness buttons (hardware) to force your display to natively measure 2.2 so the video card LUT curves aren't distorted into forcing this response through software.

I did not know you can do that. I thought that the native gamma was in the LUT of the monitor. So you are saying that adjusting the contrast and brightness change that? I only have Brightness control, but that would change the luminance point when calibrating as well, right? But can the Tone Response Curve be adjusted separately?

Color managed applications rely on the embedded gamma the image was edited in determined by the tagged profile. This gamma number may be 1.8=ProPhotoRGB or 2.2=AdobeRGB/sRGB.

I understand that.

When you change the gamma curve of your display profile the image viewed in Photoshop will lighten or darken not only from this display profile change but also whatever the gamma curve of the color space the image was edited in and that might have been on a very dark or very bright display which makes predicting and understanding this behavior unnecessary if not impossible.


I don't think I understand what exactly does that mean. Can you explain again please?

There are two profiles, one for the image and one for the monitor. The monitor profile is stationary and it's there to correct for that particular monitor and to bring it into what every state we set as target when calibrating. Image profile travels along with the image so that the image could be displayed on another calibrated and profile monitor with the same target settings the same way, right? Also, in order for us to take advantage of the embbed image profile we need to view the image in the color managed application like Photoshop?

What I'm asking is does the Photosohop have the ability to read the profile of the monitor, the profile of the image - compare the two and adjust the image regardless of the monitor profile? So for example let's say I calibrate to gamma 1.8 and the image has embedded sRGB profile. (Gamma 2.2). Will the image appear in Photoshop lighter as gamma 1.8 (monitor has priority), or will it appear as gamma 2.2 (photoshop priority) or some combination of the two?  If it will appear as gamma 2.2, that would mean that Photoshop must know the default profile of the monitor, must know the profile of the image, calucaulte the difference and display the image to look on screen as if it was gamma 2.2 for the image and as if monitor was also calibrated to gamma 2.2 even though it's still actually gamma 1.8. I don't know if that is happening and I'm looking for a straight answer for confirmation. That is the something I was unable to find no matter how much I read about it. Is it yes it dose or no it dose not and if it's not than I would like to figure out what is really going on, so I can know who or what to trust. orry, for my attitude but its frustrating, I have spend last seven days reading everything I can get my hands on regarding gamma and what I just asked and there is so much contradicting, wrong and unclear information.


Thank you.
« Last Edit: January 13, 2013, 11:13:39 PM by Krunoslav Stifter » Logged
samueljohnchia
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« Reply #3 on: January 13, 2013, 11:36:50 PM »
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The tone response curve of a display will never match a gamma curve, as it has a non zero black point. Different display calibration software use different means to adapt a display's TRC to an ideal gamma curve, via the video card's LUT or for high-end displays with the correct matching software, the on-board internal LUT of the display. The latter is preferred for demanding users.

Adjusting a display's brightness control reduces the intensity of the backlight. The behaviour of the backlight is non-linear (as are most real world devices), but it will not change the display's TRC much. This control is to let you set the white level of the display. It is not intended to force the display TRC to gamma 2.2. For displays that have TRCs quite different from gamma 2.2, adjusting the brightness adjustment is not going to help.

Adjusting the contrast control is a internal software adjustment on the display, and it changes the while level while maintaining the intensity of the backlight. Below the optimal setting, one gets less dynamic range from the display (reduced contrast). Above the optimal setting, one would blow out bright whites. Think of it as the white point on a Photoshop curves adjustment, or the white points sliders in levels. My suggestion is to leave it at the manufacturer's default, which is almost always the optimal setting. iMacs completely do away with this setting, possibly to prevent users from getting less than what the display is capable of. This setting does not affect the TRC of a display.

This article is an excellent source of information.

Unfortunately, getting the display's TRC to approximately gamma 2.2 will require loading calibration curves into the video card for lower end displays.

Matching the TRC curve of your display to the gamma of your working space is not necessary, as you have discovered. However, if you want to look closely for differences, look at very dark tones like 0,0,0 vs 1,1,1, vs 2,2,2... A ProPhoto RGB target with those tonal differences will be crushed slightly on a display calibrated to approx gamma 2.2. An Adobe RGB target will have slightly better separation. Gamma curves are quite flat near black, so that's where the differences lie. It does not matter to most users.

Extremely demanding users will consider the ambient illumination of the surrounding environment that the display is in, before inputting the gamma curve that one wishes the calibration to approximate. If you are viewing your display in a darkened environment, gamma 2.4 may be a better choice, assuming this does not cause undesirable performance issues to the display.
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Tim Lookingbill
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« Reply #4 on: January 13, 2013, 11:44:28 PM »
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You might want to adjust your display's contrast and brightness buttons (hardware) to force your display to natively measure 2.2 so the video card LUT curves aren't distorted into forcing this response through software.

I did not know you can do that. I thought that the native gamma was in the LUT of the monitor.

I don't know what brand of display you have. If it's an NEC SpectraView disregard what I said. If you have an off the shelf LCD like I have, (Dell 2209WA) you can adjust brightness and contrast but it will require trial and error to get the calibration software to measure it as 2.2 and may not be worth the trouble. It's not a deal breaker. I'm not familiar with the electronics or the LUTs of backlit LCD displays to give a better explanation. It works for me.

Quote
What I'm asking is does the Photosohop have the ability to read the profile of the monitor, the profile of the image - compare the two and adjust the image regardless of the monitor profile? So for example let's say I calibrate to gamma 1.8 and the image has embedded sRGB profile. (Gamma 2.2). Will the image appear in Photoshop lighter as gamma 1.8 (monitor has priority), or will it appear as gamma 2.2 (photoshop priority) or some combination of the two?

Calibrating your display to another gamma target will not change the appearance of color managed images. I was saying if you start switching display profiles having a different gamma while a tagged image is open in Photoshop, Photoshop will still maintain the appearance of the opened tagged image but some OS systems may not allow this to happen on the fly. You may have to click back on the image in Photoshop to see the image return to it's original contrast/brightness appearance caused by the changing display profiles which invokes a global change to the entire OS GUI.

Photoshop like all color managed image viewers does a round trip comparison of pixel data by way of Lab space in relation to the tagged color space the original edits were applied to maintain the intended color and contrast established by original edits applied  and influenced by human's visual system which can't be controlled or accounted for (See the article "Why are my prints too dark") to know what I'm talking about. When you brighten your display to 1.8 gamma the color managed image in Photoshop may look somewhat darker looking by comparison due to the surround effect similar to what happens when the lights turn on in a movie theater.

You really need not concern yourself over this nor does it need to be explained to someone in a tutorial. Just follow the instructions and let the technology do the work. Do you see how much time and energy it takes just to explain this stuff? Look how long your original post is.

Heck! Look how long mine is!

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samueljohnchia
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« Reply #5 on: January 13, 2013, 11:50:29 PM »
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What I'm asking is does the Photosohop have the ability to read the profile of the monitor, the profile of the image - compare the two and adjust the image regardless of the monitor profile? So for example let's say I calibrate to gamma 1.8 and the image has embedded sRGB profile. (Gamma 2.2). Will the image appear in Photoshop lighter as gamma 1.8 (monitor has priority), or will it appear as gamma 2.2 (photoshop priority) or some combination of the two?  If it will appear as gamma 2.2, that would mean that Photoshop must know the default profile of the monitor, must know the profile of the image, calucaulte the difference and display the image to look on screen as if it was gamma 2.2 for the image and as if monitor was also calibrated to gamma 2.2 even though it's still actually gamma 1.8. I don't know if that is happening and I'm looking for a straight answer for confirmation. That is the something I was unable to find no matter how much I read about it. Is it yes it dose or no it dose not and if it's not than I would like to figure out what is really going on, so I can know who or what to trust. orry, for my attitude but its frustrating, I have spend last seven days reading everything I can get my hands on regarding gamma and what I just asked and there is so much contradicting, wrong and unclear information.

If color management is set up right, the image's colors will be tone mapped from the gamma of the working space to the display's TRC. The application does not have "priority".
« Last Edit: January 14, 2013, 12:05:19 AM by samueljohnchia » Logged
Krunoslav Stifter
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« Reply #6 on: January 14, 2013, 12:13:36 AM »
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If color management is set up right, the image's colors will be tone mapped to the display's TRC, regardless of the gamma of the working space. The application does not have "priority".

Yes that is what I was asking.

So if that is true why everybody keeps saying that one doesn't effect the other when one dose. And that is my perception when I use calibrated profile and when I don't use it. The photoshop doesn't seem to have priority.

I have listed quoted articles in my original post that seem to say that is not true and that still confuses me.

Calibrating your display to another gamma target will not change the appearance of color managed images. I was saying if you start switching display profiles having a different gamma while a tagged image is open in Photoshop, Photoshop will still maintain the appearance of the opened tagged image but some OS systems may not allow this to happen on the fly. You may have to click back on the image in Photoshop to see the image return to it's original contrast/brightness appearance caused by the changing display profiles which invokes a global change to the entire OS GUI.

OK. I just did that. And here is what happens.

My monitor profile was loaded and I had tagged image open in Photoshop. Than I "turned off" my calibration in application for Spyder 3. The image and everything became brighter and I believe that I measured my display to have native gamma of 1.9. Unless my eyes fool me what I'm seeing is that Photoshop doesn't do anything. The image open in PS gets brighter just like everything else. I have opened it again in PS and the same thing. It's brighter. So it would seem that PS can't do anything regardless of what people say. And like samueljohnchia said; The application does not have "priority".

So it would seem that either I'm missing something very important or what all the articles I listed in original post are wrong. I would like to think they are but it is more likely that I am wrong. And it's driving me nuts since I can't figure it out.

You really need not concern yourself over this nor does it need to be explained to someone in a tutorial. Just follow the instructions and let the technology do the work. Do you see how much time and energy it takes just to explain this stuff? Look how long your original post is.

Heck! Look how long mine is!

Well, I tried to find the answers to some very confusing questions and the process felt pretty much like digging a rabbit hole just to find out how far it goes, not very productive. Many people report the same frustration. My job is to make it easy to understand. But I guess there is a reason why this is so confusing. I want to make it not confusing and to do that I need to understand it myself first. I am essentially a translator, I make complex topic seem simple that is that the tutorial is supposed to do. But like I said I need to be very comfortable and confident in the topic.
« Last Edit: January 14, 2013, 12:16:25 AM by Krunoslav Stifter » Logged
Tim Lookingbill
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« Reply #7 on: January 14, 2013, 12:56:24 AM »
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Than I "turned off" my calibration in application for Spyder 3. The image and everything became brighter and I believe that I measured my display to have native gamma of 1.9.

I'm on a Mac and that doesn't happen unless when I switch to my factory default Dell 2209WA profile (built automatically by Mac OS from the EDID ROM chip data embedded in the display's electronics) which produces a brighter than normal 1.8 gamma-ish response that doesn't exactly have the same contrast induced tonal distribution characteristic (going by the appearance of a gradient) if I were to build a custom one with my calibrator. This is due to the fact that the manufacturer wrote that EDID default profile data based on THEIR contrast/brightness settings and maybe other settings all of which are UNKNOWN. Photoshop does see the 1.8 gamma curve of the new display profile but the globally brighter appearance not associated with 1.8 gamma Photoshop has no ability to adjust for in tagged images.

So yes, the image should not return to its previous color managed appearance if the appearance of gamma associated with that number has been changed.

I don't know what OS you're on and I'm not familiar with what happens when Spyder 3 "turns off" calibration. Instead of doing that try switching to another display profile that downloads a gamma curve that changes the display globally. Better yet make an alternative display profile with a different gamma target that makes the display brighter using Spyder 3 and load that instead of "turning off" calibration-a setting that doesn't tell you anything what's happening on your video system.
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Krunoslav Stifter
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« Reply #8 on: January 14, 2013, 01:28:35 AM »
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I don't know what OS you're on and I'm not familiar with what happens when Spyder 3 "turns off" calibration. Instead of doing that try switching to another display profile that downloads a gamma curve that changes the display globally.

I'm using Windows 7 and Spyder 3 Elite calibration device.

Better yet make an alternative display profile with a different gamma target that makes the display brighter using Spyder 3 and load that instead of "turning off" calibration-a setting that doesn't tell you anything what's happening on your video system.

 
Yes you could be right, I thought about that just before you posted. So I did what you suggested. I calibrated to another profile that is the same in terms of white point and luminance settings except the gamma was 2.2 in the old one and I set the gamma value to 1.00 for the test profile. Naturally when loaded everything became a lot brighter including the image in Photoshop. So I'm pretty sure now that Photoshop doesn't compensate for the gamma in the monitor profile. Monitor profile effects all the pixels the same in terms of gamma, wheather they be image in Photoshop or UI of photoshop or Win UI. I used Spyder application to load the profile with gamma 2.2 in the GPU and also the test one with gamma 1.00 and I can defiantly see the difference.

ISO 12646: Monitor Calibration: Theory and Practice for the Fine Arts

"colour managed applications like Adobe Photoshop™ will automatically transform image data to the current monitor profile ensuring correct values are displayed on screen irrespective of the monitor’s gamma. The monitor’s gamma setting therefore only alters the appearance of non colour managed content and applications, and does not alter the monitor’s white or black points, only the relative brightness of the mid tones on screen. "

Can somebody explain what am I missing please?
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Tim Lookingbill
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« Reply #9 on: January 14, 2013, 01:40:25 AM »
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If I read you correctly...when you loaded the 1.00 gamma display profile which made the entire display brighter globally and you switched back to Photoshop and clicked on the profile tagged image, the image didn't return to normal?

If the image didn't return to normal=non-bright preview, then something isn't working right with Photoshop updating the color managed preview when switching OS level profiles on the fly.

What happens when you reboot Windows with 1.00 gamma loaded and reopen the image in Photoshop?
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tho_mas
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« Reply #10 on: January 14, 2013, 01:49:37 AM »
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My monitor profile was loaded and I had tagged image open in Photoshop. Than I "turned off" my calibration in application for Spyder 3. The image and everything became brighter and I believe that I measured my display to have native gamma of 1.9. Unless my eyes fool me what I'm seeing is that Photoshop doesn't do anything. The image open in PS gets brighter just like everything else. I have opened it again in PS and the same thing. It's brighter. So it would seem that PS can't do anything regardless of what people say. And like samueljohnchia said; The application does not have "priority".

So it would seem that either I'm missing something very important or what all the articles I listed in original post are wrong. I would like to think they are but it is more likely that I am wrong. And it's driving me nuts since I can't figure it out.
very simple: color management aware softwares translate the gamma / trc curve of images to that of the monitor profile. When you disable your monitor profile (just like in your "test") there is no monitor profile anymore to translate to. But: there is sRGB that is used by defalut on Windows when no dedicated monitor profile is assigned. But since your display has a generic gamma of 1.9 it won't match the TRC of sRGB (which is not Gamma 2.2 BTW... it has its own TRC). So you have a mismatch between sRGB and the actual Gamma of your monitor.

The quotes above are all correct: you can easily test it not by throwing away the monitor profile (which alters the video LUT and therefore of course changes the gamma of the monitor) but by simly converting an image from one color space into another: your monitor is profiled to match Gamma 2.2. So open an image in AdobeRGB (Gamma 2.2) in Photoshop and convert it to ProPhoto (Gamma 1.8 ) - visually the image will still look "the same".

edit: and yes, Photoshop loads the monitor profile on startup. So you have to restart Photoshop to use an updated monitor profile.
« Last Edit: January 14, 2013, 01:51:36 AM by tho_mas » Logged
Krunoslav Stifter
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« Reply #11 on: January 14, 2013, 02:07:29 AM »
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What happens when you reboot Windows with 1.00 gamma loaded and reopen the image in Photoshop?

edit: and yes, Photoshop loads the monitor profile on startup. So you have to restart Photoshop to use an updated monitor profile.

You guys are lifesavers. Yes that was it. Rebooting the PS was the one thing I did not do. Did not occurred to me even though it's actually obvious. Duh! maybe too obvious. Smiley

Thank you so much. This was driving me nuts. But now I see it's true, and before it did not match what I was reading.


So yeah, Photosohop does in fact adjusts the gamma of the images by compensating for that of a monitor. But in doesn't read the new monitor profile on the fly it has to be rebooted to recognize it. Thank you guys once again. I'm really glad I joined this community.

BTW...

there is sRGB that is used by defalut on Windows when no dedicated monitor profile is assigned. But since your display has a generic gamma of 1.9 it won't match the TRC of sRGB (which is not Gamma 2.2 BTW... it has its own TRC). So you have a mismatch between sRGB and the actual Gamma of your monitor.

To makes things worse my monitor is wide gamut so it doesn't really defaults to sRGB but more like Adobe RGB. Unusable outside color managed applications. Not sure if that is the case with gamma as well as gammut but as far as I can tell it's only about gammut and it would not be the case here. So I think you are right, I check the default profile for monitor in windows when there is no calibrated one or the one that the monitor manufacturer sends and its at least officially set to sRGB.

Anyway, thank you guys for your help. Really appropriate it. Smiley

« Last Edit: January 14, 2013, 02:10:17 AM by Krunoslav Stifter » Logged
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« Reply #12 on: January 14, 2013, 09:24:56 AM »
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The TRC "Gamma" (if it is a gamma curve) isn't anything to worry about unless you have a pretty crappy low bit display and you can't set the calibration software for a native gamma (since altering this only produces more banding). Otherwise what the TRC of a working space, output space, display space etc can all be different and ICC aware applications will do what they need to do so everyone gets along.

Outside ICC aware app's, all bets are off. But then no one would know or care about TRC anything at this point, it's chaos color wise.
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samueljohnchia
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« Reply #13 on: January 14, 2013, 09:36:04 AM »
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So yeah, Photosohop does in fact adjusts the gamma of the images by compensating for that of a monitor.

The OS does the gamma mapping to the display profile. The calibration curves are loaded onto the video card LUT, and the data stream for the display has to be passed through that before sent via a HDMI or DisplayPort (or vga) cable and then into the display, which will transform the data again in its own internal LUT. That's why even non-color managed apps are affected. Don't mix that up with the display profile, which is not the same as the calibration. The profile is not loaded onto the video card and can only be used by color managed applications like Photoshop. Colors are transformed even more specifically via a conversion to the display profile than simply the calibration curves alone.

Therefore, if your display calibration was set to gamma 1.0, Photoshop will respect that, as it has to pass data through the OS and the video pipeline. Photoshop is only adjusting colors based on the display profile, and not adjusting the gamma of images based on the display calibration. If you convert between working spaces, then Photoshop does perform gamma mapping to the gamma of the new working space. But that is a different story.
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« Reply #14 on: January 14, 2013, 10:33:49 AM »
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Photoshop is only adjusting colors based on the display profile, and not adjusting the gamma of images based on the display calibration.

True, but in the case of the OP's 1.00 gamma experiment, Photoshop is also taking into account the gamma embedded in the color space the image was written/encoded into and tagged with otherwise there would be nothing for Photoshop to compare against the 1.00 gamma's global brightening of the display and the image's RGB data.

For instance if it was an untagged image opened in Photoshop then the Working Space chosen in PS's Color Settings dialog box would be the default gamma that defines how the RGB data was encoded (basically the equivalent of assigning it to the RGB data). So if Color Setting's default RGB Working Space was 1.8 gamma ProPhotoRGB and the image was originally edited and encoded in 2.2 AdobeRGB or sRGB but not tagged as such, then the appearance of the image would not appear as intended under global 1.00 gamma.

This is one of the major reasons I keep asking folks here who upload and post there .png screengrabs of their desktop or images in these forums to embed their display's profile in the image which Mac OS automatically does to screengrabs. Converting to sRGB would be an added benefit for those not viewing in color managed browsers on sRGB-ish gamut displays.

Just trying to keep it concise.
« Last Edit: January 14, 2013, 10:42:52 AM by tlooknbill » Logged
Krunoslav Stifter
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« Reply #15 on: January 14, 2013, 04:15:04 PM »
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True, but in the case of the OP's 1.00 gamma experiment, Photoshop is also taking into account the gamma embedded in the color space the image was written/encoded into and tagged with otherwise there would be nothing for Photoshop to compare against the 1.00 gamma's global brightening of the display and the image's RGB data.


This was the Gamma 2.2 monitor profile and sRGB (gamma 2.2) for the image




Than I calibrated to the same monitor profile but changed the gamma target to 1.00, the image was still sRGB (gamma 2.2)

As you can imagine it did not fit what I was reading about Photoshop being independent of the calibration settings. But...



...I forgot to do the most basic stuff. Restart Photoshop. When I did that this is what I got.



So even though the monitor profile is gamma 1.00 the image is SRGB (gamma 2.2)m when viewed is color managed application like Photosohop it won't matter. Smiley

Although I think if the native gamma is way off such as mine (1.9) even though Ps takes care of the image the brighter interface will influence my perception to judge
the contrast of the image. So it makes more sense to me that in those cases I calibrate to gamma 2.2 as well.


This is one of the major reasons I keep asking folks here who upload and post there .png screengrabs of their desktop or images in these forums to embed their display's profile in the image which Mac OS automatically does to screengrabs. Converting to sRGB would be an added benefit for those not viewing in color managed browsers on sRGB-ish gamut displays.

Just trying to keep it concise.

These image should be tagged. I always do that.



P.S.
Resize settings obviously change based on what my output is.
« Last Edit: January 14, 2013, 04:22:19 PM by Krunoslav Stifter » Logged
samueljohnchia
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« Reply #16 on: January 14, 2013, 06:00:11 PM »
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Krunoslav, thanks for doing the experiment. I re-read my previous post and your experiment results and I think I have contradicted myself in the same paragraph.

This might be more accurate: Photoshop performs both gamut mapping as well as gamma mapping to the display profile, while the OS does a gamma correction to the display profile.

It is interesting to point out - comparing your first and third screenshots, while the images look superficially the same, the third screenshot has deep shadows that are more "crushed". This is due to having a working space gamma significantly different from the display "gamma" or TRC. Btw sRGB is not exactly gamma 2.2. It would be technically more accurate to use Adobe RGB for a gamma 2.2 comparison between working document to the display profile and calibration.
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Krunoslav Stifter
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« Reply #17 on: January 14, 2013, 06:08:47 PM »
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Krunoslav, thanks for doing the experiment. I re-read my previous post and your experiment results and I think I have contradicted myself in the same paragraph.

No worries. I was just trying to figure out WTH is going on. It was driving me nuts. I'm glad I joined this forum, though. Smiley

Btw sRGB is not exactly gamma 2.2. It would be technically more accurate to use Adobe RGB for a gamma 2.2 comparison between working document to the display profile and calibration.

Well I made such a big change with gamma 1.00 calibration that it dosent really matter I wanted to see the visual difference in a profound way.


sRGB according to wiki: Unlike most other RGB color spaces, the sRGB gamma cannot be expressed as a single numerical value. The overall gamma is approximately 2.2, consisting of a linear (gamma 1.0) section near black, and a non-linear section elsewhere involving a 2.4 exponent and a gamma (slope of log output versus log input) changing from 1.0 through about 2.3.

Photohops can't really show the TRC with only one gamma value but it's significantly close to gamma 2.2 so when you open custom Profile dialog box where it shows you sort of a DNA of the profile it simply says  simplified sRGB. Smiley


« Last Edit: January 14, 2013, 06:10:48 PM by Krunoslav Stifter » Logged
samueljohnchia
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« Reply #18 on: January 14, 2013, 06:44:36 PM »
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Photohops can't really show the TRC with only one gamma value but it's significantly close to gamma 2.2 so when you open custom Profile dialog box where it shows you sort of a DNA of the profile it simply says  simplified sRGB. Smiley

No worries, just trying to be accurate about things. Like for example, most folks don't know that they shouldn't adjust the contrast adjustment on lcd displays, unless it is for special reasons.

I tested this claim that Photoshop does not recognise the complex gamma curve of sRGB and it proved to be false. Photoshop indeed does recognise the TRC of sRGB, and the (legacy) custom profile dialogue box does not have the capability to show the 1024 point curve embedded in the profile.

It is the linear portion near black of sRGB's TRC that is making your display preview so nicely separated when calibrated to gamma 2.2 (giving one a feeling of more open shadows), but it flattens out when the display is re-calibrated to approx gamma 1.0. This critical test image goes some lengths to show that having a display gamma that is too far off from your working space may still influence critical judgement in image editing. How would you know then if the deepest shadows (look at the pants) really contains detail or not? What happens when it is printed? Should one expect screenshot 1 or screenshot 3's shadow rendition?
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Schewe
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« Reply #19 on: January 14, 2013, 06:45:56 PM »
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I am not sure about that since to my eyes it seems like when I deacitve my monitor profile made by Spyder calibrator - it switches the monitor to gamma 1.9 (native for my monitor) and to my eyes it seems like the image and the UI of Photoshop goes lighter as well, and that would mean that PS is in fact effected primarily by the gamma of the display.

If your display is an LCD, I'm inclined to really doubt your assessment that your display's "native gamma" is 1.9. How did you determine that? Most native gammas of LCDs are 2.2-2.3 unless something else might be going on with your display pipeline..
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