Re: 16 bits = 15 bits in Photoshop?
Re: 16 bits = 15 bits in Photoshop?
- Subject: Re: 16 bits = 15 bits in Photoshop?
- From: Graeme Gill <email@hidden>
- Date: Wed, 20 Apr 2005 12:22:35 +1000
- Organization: Argyll CMS
Jim Rich wrote:
I am one of those people that has taken say 30 images. Half of them were 8
bit and the other half were 16 bits. I then whacked the pixels by making
large tone and color corrections over 25 times per image using Photoshop. I
then printed the images.
A crucial factor in running such an experiment, is the level of
noise (or grain if you like), in the images. Such noise acts
as a "dither", that conceals quantization artefacts quite well.
A lot of real world photographs fall into this category, due
both to the nature of real world objects, and the practical
limitations of capturing photons.
The opposite extreme is a synthetic computer image generated
without any surface textures.
If you run your experiment with the first type of image,
I can well imagine coming to the conclusion that 8 bits
works remarkably well.
Using the second type of image, I can well imagine coming
to the conclusion that 8 bits is woefully inadequate.
A good example of a controlled series of such experiments is
reported on in "Precision Requirements for Digital Color Reproduction",
Mike Stokes, Mark D. Fairchild, Roy S. Berns, ACM Transactions on Graphics,
Vol. 11, No. 4, October 1992, pp 406. Using real world images, they
came to the conclusion that 10-11 bits of precision are needed, when
represented in CIELAB colorspace.
Graeme Gill.
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