Re: [Openexr-devel] Adobe's Digital Negative Format

[Greg Ward]

I'm not a big fan of camera RAW, and I've bent quite a few ears on this 
topic before, but I agree with Chris (and Florian) that OpenEXR 
probably isn't the best place to put camera sensor data.  As I see it, 
storing the original sensor data has the following advantages:

	1) No image processing happens in the camera, therefore no "short 
cuts" are necessary in the production of a finished output image.
	2) Later processing can choose alternative white points, improved 
Bayer (RGB matrix) interpolation, and make adjustments to the tone 
curve without incurring multiple quantization losses.

Since some processing would have to go on in converting to OpenEXR or 
any other scene-referred format, such an output image, however 
desirable, would lose the first advantage.  However, if the stored 
color accuracy is high enough, a floating-point or similar output 
format would maintain the second advantage.

The main drawbacks of camera RAW as it is currently practiced are:

        1) Different encodings from maker to maker and camera to camera.
	2) Lack of future support, making RAW a poor choice for image 
archiving.

Additionally, I have found that manufacturers often exaggerate claims 
for additional latitude (dynamic range) and accuracy in their RAW 
formats.  In fact, there is little if any benefit to using RAW over a 
low-compression JPEG in terms of noise, range, and color accuracy.  At 
best, I've found that camera RAW gets maybe 1/3 ev (f-stop) over white, 
and sometimes not even that, compared with JPEG or standard TIFF 
output.  At the bottom end, a linear 12-bit encoding of CCD output is 
scarcely better than the 8-bit gamma-compressed encoding of standard 
TIFF or JPEG.  My impression is that camera makers use RAW as an excuse 
not to move towards deeper pixel encodings.

My biggest problem with RAW, however, is that camera makers have been 
using it as a means to lock users into their products and their 
software, the latter being often inferior to commercial products that 
would work if it weren't for the proprietary nature of the RAW 
encodings.  As a software developer myself, I find this to be 
particularly irksome.

Adobe's offer to clean up this mess with a public standard should be 
applauded.  I only wish they went further to insist that camera makers 
work instead towards a proper scene-referred standard such as OpenEXR 
or an HDR JPEG format.  The extra work in terms of processing on the 
camera is not as much as one might imagine -- a capture of two 
exposures should be sufficient to gain an extra 3-4 f-stops of dynamic 
range, compared with the 1/3 f-stop offered by RAW.  Given the time it 
takes to write to some memory cards, HDR JPEG might even be quicker 
than using camera RAW, since the files would be smaller.

-Greg