Transfer Characteristics of G5 or other G series

[Robert_Lay]

Has anyone ever created and published a digital response curve for the G5 (or any other of the G series)?

I am interested in seeing the response (as digital densities, 0 to 255) for a range of exposure levels from Zone 0 through Zone IX or XII using B&W in conventional jpg mode (not RAW).

The only reason I am interested primarily in B&W instead of full color is to keep it simple.

It's fairly obvious that the full dynamic range of the camera's sensor is being squashed as the full image data is being converted to 8 bits per channel and I would like to know how that is done and how it affects the shape of the response curve. That is, is it fairly linear, or does it look more like typical film response curves?

Also, in the same vein, does anyone know how many bits per channel are in RAW mode. Obviously it is more than 8, but is it 10, or 12 or what?

[DavidB]

I guess the question comes up: WHICH response do you want to graph?
The response of the raw sensor? You could access this from a RAW file with a "linear" conversion. The response of the gamma-corrected image? This will depend on your choice of white balance (yes, even if you're then going to greyscale the image), curves, etc. All those wonderful tools you can play with in a RAW converter.I gave up on trying to map the Zone system (which is based around the stages of having a negative and then a printing step) to digital a few years ago, but you can certainly experiment and find a workflow that will suit yourself.

For the G5, I think you'll find the RAW files have 12 bpp. That's linear data (which gets compressed at one end and expanded at the other during the gamma conversion).

[Robert_Lay]

Dear "David B",

First, let me thank you for the information on the G5 RAW having 12 bpp. When I think about that and am forced to think of each pixel of the RAW format being either R, G or B, I get depressed.

Based on the two software packages available to me for RAW to TIF, I'm not exactly sure what ist meant by a "linear" conversion. Does that mean just commanding a conversion to TIF without making any adjustments from the default settings? I guess what I had in mind would be closer to the gamma-corrected image which I would convert to grayscale by simply setting the Hue control to -100 during the conversion (using Photoshop CS).

The real mystery seems to be in the gamma conversion that you say gets compressed at one end (I assume the bright end gets compressed) and expanded at the other (I assume it's the shadow end that gets expanded. I have experimented with it a bit already and seem to get a pronounced toe at the shadow end and a pronounced shoulder at the bright end.

One would think that the relevant mathematical expression would be available from Canon.

Thanks for your input.

[ATucker]

If you have not already, take a look here:

http://www.normankoren.com/digital_tonality.html

[Robert_Lay]

Dear ATucker,

At first glance that reference to Koren's web site looks like a gold mine of just what I'm looking for.

Many thanks!