Re: [Openexr-devel] f-stops and steps. How are they related?

[Yves Poissant]

As a follow-up, I found it interesting that in order to view this page 
correctly:
http://www.sgi.com/misc/grafica/setup/index.html
I have to set my gamma (as measured on a gamma strip pattern) to 1.3. The 
gamma setting I naturally feel most confortable with anyway.

I just observed that I already had stored gamma presets in my video card 
color settings. 1.3, 1.8, 2.2 and 2.6. But I don't remember why I set them 
that way. The more I read about Gamma setting the more I'm confused. I'm not 
even sure which setting I used for RAW digital photo processing anymore 
because I have kept no note of it and I may very well have changed the gamma 
setting since.

I know that most photographers sites that care to supply a gamma adjustment 
instruction, do recommend a gamma of 2.2. But Frankly, I find this way too 
dark. And I suspect this is to compensate for the inherent gamma curve that 
are embedded in photos, be it through digital camera gamma transform or 
through scanners gamma transforms. This camera embedded gamma transform was 
*extremely* obvious when working with RAW digital camara data which is, as I 
understand it, the most linear data we can get from a digital camera. So I 
suspect I probably must have used a gamma of 1.3

As a note, we tested 3 brand of pro digital cameras and 3 different Canon 
models (we found Canon makes the best camera for RAW data quality BTW, 
mainly because they use CMOS sensors which have a very good s/n ratio in 
very low levels) and we found that the sensor data is not that quite linear 
as evidenced when comparing the intensity distributions from camera to 
camera but it was linear enough for our needs. For those who wonder, RAW 
data from good pro level digital cameras gives you at least 2 additional 
f-stops in the low range portion and 2 f-stops in the high range portion of 
the captured photo.

Also, for convenience, the pattern you instructed to do in your post, that 
is :
>     BBBBBBBBBBGGGGGGGGGG
>     WWWWWWWWWWGGGGGGGGGG
>     BBBBBBBBBBGGGGGGGGGG
>     WWWWWWWWWWGGGGGGGGGG
>     BBBBBBBBBBGGGGGGGGGG
>     WWWWWWWWWWGGGGGGGGGG
>     BBBBBBBBBBGGGGGGGGGG
>     WWWWWWWWWWGGGGGGGGGG
>     BBBBBBBBBBGGGGGGGGGG
>     WWWWWWWWWWGGGGGGGGGG
>     BBBBBBBBBBGGGGGGGGGG
>     WWWWWWWWWWGGGGGGGGGG

Can be found in several places on the net:
http://graphics.stanford.edu/~ericv/gamma/gamma.gif
http://www.spurgeonstudio.com/Oldindex.htm

Also, when I was working on RAW digital camera photos, I found this site
http://www.normankoren.com/digital_tonality.html
Where you can find this ingenious calibration chart:
http://www.normankoren.com/makingfineprints1B.html
The advantage I found of this new chart is that it will work on any monitor. 
Not only on good quality monitor.

Yves Poissant
Hash Inc.
www.hash.com

P.S.: The work on RAW digital data I mentioned above was not related to Hash 
Inc.