No difference between 8 bit and 16 bit. Help?

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<p>I am not using an 8-bit video display, and I'm not out to boast about my equipment.</p>

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<p>I didn't think you were boasting about your equipment. I'm referring to an 8-bit video card pipeline within your OS's system. I'm assuming you're talking about your display's high bit internal calibration LUT hardware which still only receives 8-bit video through your video card's frame buffer unless you're using a video card that supports higher bit throughput.</p>

<p>From reading your original post and title indicating the word "Help" I was trying to determine whether you were attempting to sort out a video driver bug that you suspected was not showing through previews what you thought should be high bit data behavior according to how you understood high bit editing workflow with normal editing. Or whether you were trying to understand how high bit data could be detected in a preview through the use of a posterization test which you asked us to conduct on our own system. I either didn't see the point of it or understand what you were checking for with regard to seeing the effects of high bit data on a low bit video pipeline which made me wonder just what you needed "Help" on.</p>

 

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<p>These may well be "minute piece of technology" but actually, I do give a sh*t about it - if that's OK with you.</p>

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<p>That statement I made was directed at Andrew's harping in a LuLa discussion he and I had which he provided in his link on what I referred to as "a piece of minute technology" such is the ACE CMM that operates under the color management hood hardly any photographer really pays much attention to or "give's a sh*t about".</p>

<p>Andrew has a long history in online discussions of overcompensating in order to get his point across by linking to other discussions in order to make the other person he's arguing with come across as someone whose information can't be trusted. I tend to ignore him at that stage because I hate seeing a grown man who already has a long history of establishing himself as a trusted expert lose it by going to those lengths over something so trivial.</p>

<p>I still don't know if you got the help you requested.</p>

 

<p>OK, I think we're getting somewhere.<br>

I just tried opening the NEF directly from photoshop. It seems that after heavy posterisation, a very tiny difference occurs between the original 14-to-16-bit and the up sampled 8-to-16 bit. Too tiny a difference to say "wow, this is clearly superior", but a difference nonetheless - confirmed in the histogram.<br>

View NX continues to produce identical results. This would suggest my earlier notion that View NX cuts the data before exporting it...</p>

<p>Ron, thanks, that's interesting. I admit that I have rarely touched ViewNX - so while I don't want to comment on whether that's something in the software or some setting, it does identify the point where something odd is happening.</p>

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<p>That statement I made was directed at Andrew's harping in a LuLa discussion he and I had which he provided in his link on what I referred to as "a piece of minute technology" such is the ACE CMM that operates under the color management hood hardly any photographer really pays much attention to or "give's a sh*t about".</p>

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<p>Translation: <em>Andrew (with agreement from others equally knowledgeable on the subject) have corrected the mistakes I, Tim Lookingbill have made. I'd rather not make this a learning experience and gain knowledge from Andrew and those who agree with him who corrected me so I'll ignore and not give a sh*t about my errors.</em> <br /> The most recent example was just yesterday with respect to how CMM's work. More examples are available...When Tim's wrong and corrected, it is therefore (in his mind) <strong>minutiae</strong> that (Tim speaking for everyone), no one cares about. <br /> <br /> Getting back (<strong>again</strong>) to topic, I think Ron you may have found the problem here, the Nikon software. And yes, the differences shouldn't be huge unless you inflect significant edits upon the data till you reduce the levels (as I suggested using Posterization) to the degree you see the effect on-screen. Depending on the output device and image, color gamut, degree of edits etc, this could show up on a far more demanding output. With high bit data, you don't have to worry about this happening using sound image editing techniques; there's just so much extra data <em>padding</em> the process.</p>

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<p>It seems that after heavy posterisation, a very tiny difference occurs between the original 14-to-16-bit and the up sampled 8-to-16 bit. Too tiny a difference to say "wow, this is clearly superior", but a difference nonetheless - confirmed in the histogram.</p>

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<p>How many discrete levels of posterized separated tone are you analyzing to arrive at that conclusion using this test?</p>

<p>Heavy edits to high bit data is only useful when applying to high resolution pixel levels of tones spread across a 255xRGB preview which employs sophisticated math to map changes to these fine, discrete tones through edits on millions of color combinations so I'm having a hard time understanding what you're learning from this test.</p>

<p>(to be continued)</p>

<p>I have been giving this general issue quite a bit of thought lately, and I have also done some numerical experiments.</p>

<p>Let me focus my discussion on the issue of banding, and to further focus the discussion let us consider two cases, one in which an image is acquired in 8-bit mode and the other in which the image is acquired in 16 bit mode. Let us futher consider only the case of visibly detectable banding occurring in a smooth gradient. Let us further assume for the sake of discussion (without proof) that as a practical matter no matter how much manipulation you perform on an image acquired in 16 bit mode there will be no visible banding.</p>

<p>Whether you will see banding occurring in an 8 bit image depends on a number of factors. For example, if you computer-generate a perfect gradient and express the pixels amplitudes in 8 bit words, and we then subsequently perform heavy manipulation of the gradient there is a possibility to generate visible banding. However, this case is probably not very interesting to photographers because most of us are not very interested in images generated by a computer.</p>

<p>OK then, let's consider images acquired photographically, and assume that the object being photographed is a smooth gradient. If there is no noise in the measurement chain then banding is a possibility, particularly if the image is heavily manipulated.</p>

<p>However, something entirely different happens if there is noise in the image processing chain (e.g. film graininess and sensor noise in a film/scanner system, or sensor noise in a digital camera) then something entirely different happens. If the RMS noise is comparable to the step size in the digital to analog converter then the gradient will be smooth (i.e. no banding), but there will be some noise in the image. This property is preserved under heavy image manipulation, provided that the 8 bit image is converted to 16 bits prior to image manipulation. (I suppose things might be a little different if the image isn't converted to 16 bits prior to manipulation, but I won't consider this case.)</p>

<p>It actually doesn't take much noise to assure an absence of banding. About 1/3 bit of RMS noise is enough to basically eliminate banding. For those who care much about signal processing, what we have been discussing is basically the concept of dithering, and it is a well-known method of improving certain aspects of performance at the cost of introducing a little noise into the result.</p>

<p>One other thing. If the noise of the system is comparable to the step size of an 8 bit A/D converter then there is very little benefit in using a higher resolution A/D converter, and if the noise is much bigger then there is virtually no benefit.</p>