Monitor Gamma

I’m doing some exploratory experiments with regards to gamma. I know it’s far from “gamut” discussions. It’s a lot more complex subjects than I thought. I confess I got drawn in this exploration in the wake of 8-bit vs 10-bit capabilities. I just want to share some “progress”. In the following Excel sheet (yes, Excel is a great color management tool), you’ll find two tabs, at the bottom. The first one is labeled “Step=32” and the second is “Step-4”: https://1drv.ms/x/s!AkD78CVR1NBqktUgigDMsTGPE-U6zw?e=FVTqrn I’d suggest you start by the Step=4 tab. Towards the top left, in the range B12:B20 are the RGB values I sent to my monitor. In the range C12:C20 are the measured Luminances (Y) of the corresponding RGB values in VisualStudio (C#), whereas in the range D12:D20 are the measured Luminances of the of the corresponding RGB values as displayed in Photoshop. Basically, I generated the chart that sits in the columns T to W in code, to test some hypothesis about gamma, and that’s when I noticed a difference between the chart viewed in my application development environment and a PNG version of the chart viewed in Photoshop. (I did not share that PNG but it is the same as what I created in Excel, in all these 9 rectangles, sitting between columns T to W. In the process of experimenting with gamma, I wanted to see what those rectangles would look like had they not have any gamma correction, in other words, in terms of “equal brightness” increments. The theory goes (as far as I read) that “perceived brightness” follows a power law. Fair enough. So you’ll see I build two charts, one which shows the measured Luminances gathered from VisualStudio and Photoshop, and the other, the “theory” behind gamma encoding and gamma expansion, as I found it called. Sorry, I did not give that second graph a title. And there is a screen capture below it. Now, if you turn your attention to the step “wedge” sitting between column X and AA, you’ll see that it’s the same 9 rectangles but filled with different RGB values, gamma “expanded” values which, in theory, ought to look “equally spaced, perceptually, in terms of brightness”. Arrived at that point, it occurred to me that, because of gamma expansion, RGB 32,32,32 becomes RGB 100,100,100? I thought, aren’t we loosing a whole lot of levels to this gamma expansion? I mean, is there “life” between RGB = and RGB 100? So wanting to address this question, I turned my attention to creating a step wedge with finer increments, Steps = 4, that’s the second tab. I think it’s relatively easy to follow at this point, basically studying the relationship between Input RGB codes values and their appearances with and without gamma expansion. On the left, between columns B and E, are straight RGB values, from 0 to 256, in steps of 4. Between columns J and M are the same “rectangles” but gamma expanded. In Excel, you could zoom out like hell, to 25%, to see the whole “gradient”. Now, I was somewhat reassured by this study of gamma in steps of 4. But I was still not happy with what was going on below 4? I mean, look at the relatively large jump between RGB 4 (that becomes 39) and RGB 0? That’s not the same jump as the rest of the scale? And somehow, I got the impression that I’m losing “depth” or contrast to this gamma scheme, in terms of tone range? So I created yet another series of rectangles, in columns S to Z where I went as small as in Steps of 1, from RGB 0 to RGB 16. And even at such small increments, with a gamma of 2.2, there is still quite a “jump” between RGB 0 and RGB 1, which becomes RGB 21 in a gamma “expanded” world. Call me nuts but I still was not satisfied with the result of this experiment? At one point, I toyed with the idea of “what if I was to lower the gamma value down” question? Like 1.8 or 1.5 or, gasp!, 1.0? Well, this this monitor, there is a utility called Multiprofiler that allows changing the monitor gamma on the fly. So I was off to the races and, voilà!, gamma of 1.0, no recalibration, nothing. I can’t post how the “image” appeared on my monitor here, you’d have to have your monitor set to a gamma of 1.0 as well. But suffice to say that, all of a sudden, there was no “jumps” anywhere throughout the entire scale, no blocked shadow details, “perfect 1:1” tonal mapping, if I can dare say. Of course, all the windows, dialogs, UI looked completely washed out and there is nothing anyone can do about that, that’s just the nature of Windows and MacOS as well. There is a underlying “system gamma” of 2.2 so that all controls and UI are designed to work at 2.2. What I’d like to see is having a monitor profile created with a gamma of 1.0 while the system gamma would remain at 2.2, if that was ever possible. I realize with this crazy idea of “gamma = 1.0”, I’m beginning to sound like Timo Autokiari, for those who remember, many years ago… At this point, the question I have is, does gamma calibration matters? For color management? I know, in my humble and perhaps naïve practice, I never questioned the need for gamma calibration, whether 1.8 or 2.2, depending on “religion”. But in terms of “preserving” image quality, what’s the trade off? The majority of LCD monitors sold today emulate in circuitry how the CRT response, that’s a given. My cheapo SAMSUMG 2693HM has three choices of “Gamma” in its OSD, “Gamma mode 1”, “Gamma mode 2” and “Gamma mode 3” – no documentation, no numbers of any kind to be found in the OS. But, clearly, according to my measurements, one of these modes emulate a 2.2 gamma encoding. So that, with a 2.2 “system gamma” such as in Windows and on the Mac, the whole world is not going to be crumbling down the moment the monitor is plugged in the video card. So, gamma is an “evil” that can’t be avoided. Monitors manufacturers play by it, television manufacturers play by it. You would think that, the day LCD were invented, we would abandoned the CRT gamma for a linear response? But I understand the need for “legacy”. It makes me think what happens when CTPs first entered in prepress, everybody was wondering the same thing: “What should we set our plate calibration to?”, now that they had the possibility of making 50% dot in Photoshop print 50% on the plate. It took a while for that innovation to digest in the industry… Also, as I discovered, gamma is also built-in digital images. So that, the way I understand it, JPEG has a built-in “default” (maybe hard-coded?) gamma value of 2.2. So, it’s everywhere. It can’t be turned off. Now one of the lingering question I have is how does this gamma encoding translates to ICC profiles? Are there still these “limitations” in terms of “usable device level values” or are we “free” to do as we want? I mean, between RGB 0 and RGB 1, whether it’s coming from an ICC profile, with a gamma of 2.2, or straight from a 2.2 gamma-calibrated monitor, isn’t there the same limitation? Which makes me want to study what happens in a 16-bit per channel RGB world. My initial foray in this brave new world showed me that the relationship between input RGB levels and measured Luminances are *linear* -- yes, linear, at least at a monitor gamma of 2.2, in Windows. Thanks for bearing with me this far / Roger