Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: Redcrown on October 04, 2020, 12:14:41 pm
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On Windows 10...
Help me understand the relationship and difference between a LUT stored onboard a monitor and the ICC/ICM file for that monitor stored in the Windows/System32 folder tree.
If you profile a monitor multiple times with different settings, how do you switch between profiles? Simply switching the ICM profile in the Windows Color Management utility does not seem to change the LUT in the monitor. In fact, on my new BenQ monitor, it does not appear to change anything.
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In a nutshell, yes, the calibration takes place in the display itself and the entire system updates this and then loads the appropriate ICC profile describing these conditions for ICC aware software.
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I calibrated my BenQ using their Palette Master software and an i1 Pro. I made 2 profiles, identical except the color temp. One is D50 and one is D65. During the profile process, after measurement it displayed "Writing LUT", and that step took 4 minutes. Seems to indicate it takes a while to load a LUT.
Using the hockey puck controller attached to the monitor I can switch between these 2 profiles. The switch takes only 1 second and flashes a black screen in between. The visual difference is obvious, and as expected. I can only guess that both profile LUTs are stored in the monitor, and that's why it takes only 1 sec to switch instead of the 4 minutes it took to write each one.
However, the ICM profile shown by Windows Color Management (WCM) seems to make no difference. The WCM shows whatever custom ICM profile I did last as the default. If I switch to the other ICM custom profile (D65 to D50), there is no change on screen. In other words, a D65 LUT displays the same for either a D65 ICM or a D50 ICM. Ditto for the D50 LUT. In fact, I can add Adobe98 and sRGB ICMs in WCM and set them as default, and there is no change to the display.
So, the ICM profile selected inside WCM appears to make no difference. Why is that?
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With a Benq monitor that has internal LUTs, if you want to change the monitor characteristics you need to change the LUT settings in the monitor (with the Benq puck or front panel settings) and you have to change the profile in Windows Control Panel -> Colour Management. If you do one but not the other, you end up with a Windows monitor profile that does not reflect the monitor characteristics.
You could of course do it by reprofiling the monitor using Palette Master (which alters both LUT and Windows profile), but that's rather slow.
With other monitors with internal LUTs, there is sometimes a utility to do both steps. For example the Eizo utility ColorNavigator not only calibrates/profiles the monitor, but provides an instant mechanism to change LUT and profile in one click. Pity Benq don't do that.
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I fear I'm not getting through.
Andrew talks about "loading the appropriate ICC profile", and Simon says, "you have to change the profile in Windows Control Panel." But I can cycle through several ICC profiles in Windows Color Management and nothing changes on the screen (Photoshop).
Am I doing something wrong? Do I have something messed up in my calibration?
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For a monitor with internal LUTs (like the Benq), the Windows monitor profile is merely a description of the colour space of the monitor. The profile tells the displaying program how to colour-manage the image to get the right colours on the monitor. If you change the monitor profile in Control Panel, nothing changes unless the program notices the change of profile and re-renders the image on the screen. Remember, it's the program, not Windows, that does colour-management.
Most programs check the profile only when they first run, which means you need to exit the program and restart for them to notice a change of profile. Photoshop does check, but not continuously. Sometimes, clicking the image is enough for it to check and re-render, sometimes I find I need to minimise and restore the PS window before it tries to re-render and notices the change of profile.
Going on from what I said before, to change the monitor colour space and get a program to notice and render correctly, you need to do three things:
- Change the monitor color space (in the case of Benq with the puck or front panel buttons)
- Change the Windows monitor profile to reflect the new monitor colour space
- Make the prgram re-render with the new profile, which means for most prgrams one must exit and restart, or for PS force it to re-render the on-screen image.
For some monitors (e.g. Eizo, not sure who else) there is a utility to do both (1) and (2), but (3) depends on the program that's displaying the image.
For this reason, I rarely change the monitor colour space. I leave my two monitors (one Benq, one Eizo) calibrated to their native (widest) colour space, and if I want to see what something looks like in sRGB, say, I use soft proofing. One click in LR or PS instead of a lot of faffing around.
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For this reason, I rarely change the monitor colour space. I leave my two monitors (one Benq, one Eizo) calibrated to their native (widest) colour space, and if I want to see what something looks like in sRGB, say, I use soft proofing. One click in LR or PS instead of a lot of faffing around.
Which is the whole point of color management, as opposed to calibration. With calibration, you are having to change the behavior of the display/printer to emulate one colorspace at a time, and can't display images encoded with different colorspaces simultaneously.
When using color management and color profiles on the other hand, the full gamut of your display/printer is available to you at all times, and you can simultaneously display images encoded for any colorspace, and don't have to alter the display or printer to do so.
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Simon, thank you. Photoshop simply not refreshing after a profile change in Windows Color Management is the key. I suspected that and was trying to force a refresh by minimizing then maximizing the Photoshop window. But that was not enough.
When I closed and re-relaunched Photoshop between WCM profile changes, then differences can be seen. The difference is difficult or impossible to see "live", so I took shots of the screens with my camera. By toggling those screen shots in Photoshop it is easy to see the difference.
But that brings up a new question. The image I used in Photoshop was a "synthetic" color checker - a fake CC with all RGB values forced to their targets. When I processed the images in Camera Raw I set the white balance with the eyedropper on the gray patches. I got settings of 5500 (plus or minus 100) with tint around 5.
The monitor is calibrated at D65, so I expected a white balance around 6500. What am I missing here?
P.S. I learned through trial and error that when photographing the screen I had to use exposure times of 1+ seconds to get smooth tones without scan lines.
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I think Andrew (digitaldog) can answer this much better than I can.
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The monitor is calibrated at D65, so I expected a white balance around 6500. What am I missing here?
That CCT values define a large range of possible colors, that 6500K isn't D65, that the reported values in ACR and elsewhere can all vary. That the values of the image data and the CCT or D values calibrated for a display have little to do with each other. RGB Working Spaces are display agnostic in terms of their white point (and TRC) by design.