Nice sarcasm, Ben, and thanks for the challenge. But the only decent scanner I have access to is at work. I intended no offense but comparing a 256 color image to a 16M color is questionable. I say back up your claims with a more challenging image. Not that the one you used is bad... it's actually quite good artistically... just not as challenging as it could be for testing bit depth and gradation.
As Ken says, get Vuescan. It knows how to virtualize the memory for big scans, and, unlike Siverfast, can downsample the file before it is saved to disk. It is the only program to use on limited hardware machines. If you are doing black and white, just scan one channel - red or green - to reduce noise and file size. Set it to save as 16-bit grey scale.
Ed Richards
http://www.epr-art.com
Here you go. Original un-color corrected image, then the same three scenarios. One is 32bit, one is 15bit, and one is 8bit. All three were quantized before color correction... So you are seeing the quantized images pushed via color correction.Originally Posted by Keith S. Walklet
...and the crops.
This round is a little easier to pick out (maybe because I know the answer), but the very subtle difference would be erased by making a print.
And to clarify, the point of these posts is not to say "256 colors is enough for any image!" My point is that if I can quantize images THIS much and still get something plausible, then 16 bit is truly overkill. The SNR of a film scan just obliterates the difference between 8 and 16 bit.
Ben, again, nice images but still limited in hue/tonality... mostly blues and greens with spots of gray and reds. What about some images with the full color spectrum with gradations? I'm skeptical but interested!! And don't forget to include the 256 color image.BTW, I'm seeing "graying" of colors in some of these to varying degrees. Could you please explain what I'm seeing?
I can't win! Not enough sky, too much sky... I don't take pictures of Macbeth color charts!!!
I'm not sure. What areas?
Would this image be convincing?
Ben, I'm afraid I may have offended you. I didn't intend to but, if I did, I'm very sorry. It's just that I've dealt with digital images for a very long time and I completely disagree that 256 color images can be indistinguishable from 16M colors in all circumstances. With that said, I'm trying to remain open minded... so you CAN win. You just need more challenging examples to prove it to me. Others may already be convinced. My arguement is that images with limited hues and densities can look pretty good with limited bit depth but the deeper one goes the lousier they look. A solid gray image with no hue or density changes will look just as good with one color as it does with billions of colors. In fact a single color bitmap is just the ticket for such an image. Again, no offense intended.
Mike, I never said this!! And you have not offended me. Re-read my last post. I'm not trying to say 256 color images are indistinguishable from 32bit images in all circumstances. I'm saying that if I can push my scans down to 256 and not see much of a difference most of the time, then surely there's no possibility that I'll see an improvement by switching to 16 bit. That's all I'm trying to say. These 15bit and 8bit examples are just for fun
One more round... original un-color corrected image in previous post
This article, 16-Bits Grayscale Scanning of Ansel Adams' "The Tetons - Snake River is a pretty quick compelling illustration of why we prefer higher bit-depth:
Original scans may appear indistinguishable - on our 8-bit monitors - but as we continue to manipulate and adjust the images, the histograms of those with lower-bit-depth should start to reveal banding and gaps, faster and more obviously, than those with greater bit depth. Sooner or later, those gaps in the histogram manifest as a "digital" look.
It seems fairly logical to extrapolate the same principles from b&w, to color images.
As the article says (emphasis mine): "The reason the 16-bits scan file retains its quality is because it starts out with a possible 65536 tonal shades* per channel -- allowing one to throw out most of those values still leaves one with much more than 256 (the maximum number of values in an 8-bits per channel image file)".
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