Thanks, this is a good read, helped me to get more insight into the “gamma correction causing hue shift” fear, but I still wonder if gamma correction should be done before or after color space conversion…
Do you have a colorchecker??
I have been using xrite colorchecker since 2009, but ironically, the profiling software came with colorchecker never generate good profile, therefore some other profiling tools are also popular among photographers
I have sent my questions about their incorrect profile to xrite support, and they don’t know either how to create a good profile, since they don’t know how it works under the hood
In my experience, you could try different values in matrix to adjust the rgb value for red green and blue patch, 9 values. If you make one of the channel more precise, then the other two might be off more, so it is a try and error process until you reach a status that those 3 patches are almost correct at the same time. Then rest of the patches will align automatically, because those 3 patches are near the edge of gamut. I like this approach since it does not add LUT, so you always have a smooth transition of color
Ideally, a camera profiling tool should be this simple, but those GUI based tools are all complicated and you really don’t know what they are doing behind the scene
And that’s only part of the equation. If your monitor is off then your impression of the profile will be off…when you measure the patch accuracy if it good but you still think the result is crap it might be the way the monitor is calibrated or not calibrated… Even when the whole workflow is optimized and you are happy with it then you still might only be good in your own world but once your images head out into the wild they are all over the place… Just look at many of the play raw threads…beyond the artistic license many of them are crazy dark or at times the opposite making me wonder at times is that what it looks like on their end…
Indeed, I’m using OLED TV as display device, and they have a totally different gamut. That added another moving part into the whole work flow. But I only look at rgb values in software, then the display is not a concern, I just need to set sRGB color space in software
There are so many moving parts in the whole process, the job is to fix them one by one, so that I can get a good profile
First the white balance, which in RAW processing means the gain of each channel’s value. To get a fixed value, I always use D50, which is the direct noon sunligt. Since I seldom take photo under overcast days ( colors and contrast are worse, not good for taking photos), I found a D50 profile is more than enough to use for most of the occasion. D65 is sRGB white point, but I found out the colorchecker shot under sunlight would never get that kind of lighting, it is a mix of direct sunligt and shadow (illuminated by blue sky), but colors in shadows is not that important
So a greycard shot under noon sunligt would display same rgb value in each channel, this will decide the white balance gain. There is no more other variables. Once this gain is set, it could be used for that camera forever. (even under other lighting conditions, this gain still works, you just need to adjust the white balance in software, which is another type of adjustment in post processing)
And second would be the tone curve (gamma), which so far I have not really fully understood its implication and implementation (does not seems to be a matrix). On X3F files, I never do this, so the result is that color patches are good but tone curve is a bit off, especially the brightness jump from 240 to 200 that happened between first two white patch
The tone curve (called the tone response curve, or TRC, in ICC-land) is just a ‘simple’ transfer function that modifies global tone distribution. ICC TRCs can be parametric, segmented, or tabular. Page 143 of the LittleCMS API document starts a section that describes them:
You might find that not everyone agrees with that. The harsh contrast of mid-day sun can be pretty hard to work with.
Yes the lighting is more even during overcast day, but since I’m mostly doing scenery photos, without a bluesky, the water also appears grey, the photo become dull
Thanks, I will take some time to study this