[argyllcms] Re: How can I tell if I'm using my profile? (and other questions)

Florian Höch wrote:

Adrian Mariano wrote:
I ran dispcal with the -o option so as to produce a profile as output. I loaded the profile using dispwin under linux. Now I go into firefox 3 and color management is turned on. Does firefox find the profile that was loaded using dispwin?
You can test if Firefox 3 uses your installed display profile by temporarily installing a profile with swapped colors, like this one: 
http://hoech.net/files/BRG.icc
Close your browser, install the above profile using dispwin -I BRG.icc
Open your browser and visit http://www.color.org/version4html.xalter
The big image should have magenta-red sky and green mountains, and look like the topmost small image, if the display profile is used.
Thanks. That image clearly revealed that firefox was NOT using the profile that I thought I had installed with dispwin. (Now I'm looking back at what you wrote and I'm not sure I gave '-I' when I ran dispwin, so I'll test that and see if the behavior is different.)
I made the above profile using sRGB, but I noticed the suggestion in the documentation that perhaps a gamma of 2.4 would be a better choice? I think the last time I ran a calibration I specified a temperature of 6500 K, but this time I forgot that option, which apparently means the monitor's native white point is used. Am I better off using the native white point?
Again, depends. Most (LCD) monitors offer white point control only by adjusting their internal LUT curves to reach the target value, thus sacrificing some of the 256 possible levels per channel and introducing the danger of visible banding in gradients (at 8 bit, some more expensive displays also haver 10 or 12 bit internal LUTs). So yes, it might be better to use the native white point. A gamma of 2.4 is a good starting point, you could also use dispcal -R to get a measurement of your uncalibrated displays approximate gamma response and then use that.
Really? My interest in calibration was driven by being baffled by my uncalibrated display when I looked at gamma test patterns because the display seemed to be so distant from the normal expectations, so I wouldn't think I should TRY to make the display look like it is uncalibrated. (It helped that a friend gave me her colorimeter because the latest version of Windows didn't support it any more!) Here is the result of dispcal -R: 

Uncalibrated response:
Black level = 0.29 cd/m^2
White level = 168.02 cd/m^2
Aprox. gamma = 1.97
Contrast ratio = 579:1
White chromaticity coordinates 0.3146, 0.3400
White    Correlated Color Temperature = 6333K, DE to locus =  9.8
White Correlated Daylight Temperature = 6330K, DE to locus =  6.3
White        Visual Color Temperature = 5996K, DE to locus =  9.4
White     Visual Daylight Temperature = 6128K, DE to locus =  6.1
Effective LUT entry depth seems to be 8 bits
The instrument can be removed from the screen.
So you would have me set my gamma at 2.0 so as to match the uncalibrated display? I generated two profiles with the natural white point (which seems reasonably close to 6500K) and with gamma 2.4 and with sRGB. I viewed images taken with my digital camera using the calibrations from these two profiles (in software that I'm pretty sure is not color managed) and we looked at them and tried to decide which looked better, and it seemed like the sRBG version looked kind of washed out compared to the gamma 2.4 version. My wife thought the gamma=2.4 pictures looked clearly superior. (I suppose it could be that we take overexposed pictures and the 2.4 gamma is correcting a defect rather than properly rendering them.) I also found this site which has some interesting examples where you can mouse over an image and it switches between the tagged and untagged versions. 
http://www.gballard.net/psd/go_live_page_profile/embeddedJPEGprofiles.html
The author of this page strongly insists that you should calibrate your display to sRGB (which was what I thought was the right thing to do before I saw the suggestion of gamma=2.4 in the dispcal manual). Can anybody suggest software for linux which can display jpeg images and can respect, display, and edit color tags in the images? (Does my canon digital camera include some kind of color space information in the files? We tried viewing the images in firefox and outside and it seemed that there was a slight difference, which suggests the answer is yes.)

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