[Openicc] Proof of concept, storing profile in X atoms

[Chris Murphy]

On Jun 19, 2005, at 4:05 AM, Ross Burton wrote:

> On Sat, 2005-06-18 at 15:54 -0600, Chris Murphy wrote:
>
>> There is a 2.21 spec, but I can't figure out how Adobe RGB (1998)
>> would be encoded. I know such images exist, direct from some digital
>> cameras, and that this was tripping some people up on OS X where it
>> wouldn't recognize they were Adobe RGB (1998) but Photoshop CS would.
>> Maybe they're encoding gamma and primaries elsewhere, and setting the
>> colorspace tag to uncalibrated.
>>
>
> The images produced by my Canon EOS-300D are in the Adobe RGB
> colourspace, it sets the ColourSpace tag to uncalibrated and then sets
> the WhitePoint and PrimaryChromatics tags.  I'm not sure what to do  
> for
> the gamma here, currently I've hard-coded 1.8, which obviously sucks.

The draft 2.21 addenda I found suggests a tag for gamma, so it could  
be used. I wouldn't be too hasty to condemn a hard coded image gamma  
of 1.8 because it often does a better job. I suspect that the s-curve  
applied by the manufacturers when they process their raw data into  
JPEG is making images a little too contrasty, and assuming an image  
gamma of 1.8 versus 2.2 flattens this out somewhat. I typically shoot  
RAW, as do most of my customers, which is linear capture, so the  
camera manufacturer's tone mapping (JPEG) isn't an issue. Therefore,  
I'm not sure if there has been any recent improvement in newer  
cameras to better conform to sRGB, when they say they do.

>> Co-author "Real World Color Management, 2nd Edition"
>> Published by PeachPit Press (ISBN 0-321-26722-2)
>>
>
> Hmm, maybe I should buy this book...

It's not specifically written with developers in mind, but rather the  
state of affairs with color management today. There is a table of  
contents on the web site.


Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
-------------------------------------------------------------
Co-author "Real World Color Management, 2nd Edition"
Published by PeachPit Press (ISBN 0-321-26722-2)