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Re: [APML] Fw: images
>It amazes me how much confusion there is over bit depth, dynamic >range,
>and S/N.
Hi Chuck
No confusion at all. When I was talking about bit deph I was thinking exclusively in "how many colors" a film can "store", i.e. given a dynamic range, how many effective "steps" can be "seen". Of course that the dynamical range cannot be improved with stacking, but we definitevely increase de SNR, and if we have a good bit deph, higher than the effective, the resulting image will have a higher effective bit deph than any of the original ones. Finally, with all of these, we can make a better use of the resulting dinamical range, and we can "push" the processing more harder without posterization.
>In practicality, the finest grain films are limited to about 5
>- 6 bits and most color films are about 4 - 5 bits.
Here is where I desagree with you. Due the nature of the film media I am convinced that we have more colors (or gray steps) than 6 bits. For all practical ways a photograph of a continuom gray gradient indeed looks continuos... and the human eye needs a little more of 7bits to see that.
Anyway, due the human eye's limitations, the scanning process, the monitos, etc. I think that you have a strong bias in your medition... that makes appear the film's "bit deph" worse than it is.
Just a final thought... if film can handle only 5-6 bits, why do we have 16bits scanners? Why not just 8bits ones?
PS: Photoshop is a nasty program... as Vicent said, it destroys the data. I don't trust the ways it works. Just make a gaussian blur, you'll see steps in the gradients. Also there is a problem with the monitor's capabilities of displaying the data. Even if you have a continuos (at >16bits) gradient you'll see some steps.
Regards,
Carlos Milovic F.
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Astro & Photo - CMF
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