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Input/Output/Workflow Scanning, printing, color management, and discussing best practices for control and repeatability

Reconsidering 16 bit

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  #1  
Old 01-05-2003, 06:16 PM
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Ed_L Ed_L is offline
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Reconsidering 16 bit

I've been playing around again with 16 bit images, and I scanned one as such, then made a couple of levels adjustments. The image was duplicated, and the duplicate was changed to 8 bit mode for comparison. The exact same adjustment was made to each of them, and the resulting histogram showed voids in the histogram (8 bit), with two levels being completely lost next to each other, in two different places. Nothing else was done with the images, but the results tell me that if I had to make many more adjustments, I might wind up with quite a bit of lost data. Maybe I'll reconsider the 16 bit scan, if for nothing more than tonal adjustments. Here's a screen shot of the results.

Ed
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  #2  
Old 01-05-2003, 07:10 PM
Stephen M Stephen M is offline
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Ed, the actual images do not look different though.

If you can afford to edit in high bits, then why not - but if you work is in a volume setting where actual final results matter then you may look at things differently.

If a histogram can be sold, then great! Most care about the image, although some care about data if that is what they are purchasing (although many just want a great result and would not care if the histogram was gappy).

A histogram is just a statistical report - it is up to you to decide what you read into the statistics.

For the pros/cons on this deep subject, I have collected some links from both ends of the extreme and general viewpoints:

http://members.ozemail.com.au/~binar...V_links.html#H

Ed, try this little test - the pic with the gappy histogram which looks like it has less data...convert that to another profile. Or rotate it 0.1 degree in one direction, then rotate it back. Or add 0.3 pix g/blur. All of these things will 'mung' the data and the statistical report will show a better file (if all you do is look at the histogram without any knowledge of the edit). So it is possible to make a histogram appear nicer, while the image may be worse than the gappy histogram one.

I would question the evaluation made by a histogram, unless I knew the exact editing history of the file - otherwise the histogram may or may not mean jack to the output quality of the file.

Stephen Marsh.
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Old 01-05-2003, 08:45 PM
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Ed_L Ed_L is offline
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Hi Stephen,

Thank you for your input, and for such a great site. I've visited your site a number of times before, and I've had it on my bookmarks for quite some time. I have read quite a bit about the pros and cons of high bit scanning in the past, and it seems that some of the biggest names in Photoshop land can't agree about the benefits or lack of benefits of high bit scanning. To date, I haven't seen a print that I've made suffering from posterization or other easily seen effects from using 8 bit images. I know that running a filter, even the USM, will have an effect on the histogram. I did read, I think in "Photoshop 5 In Depth", that when you have 3 - 5 levels missing together, there is a very good chance of posterization, but I can't personally confirm that from my printed materials. I know there are some who are thoroughly convinced that high bit is the way to go, and it's something that I've wrestled with. A pretty histogram is not something I'm concerned with, but the final printed product is. Any testing I've done to date did not give me reason to scan in high bit mode, but every once in a while I make comparisons. Thanks again for the input, and such a great bunch of links.

Ed
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Old 01-06-2003, 06:21 AM
Stephen M Stephen M is offline
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Hi Ed, it is a thorny subject.

I agree with the principle and the math - it's just hard to justify at this point when actual results are compared and you do the bean counting.

I like to see some balance to this topic - it usually get's to be very one sided (pro hi bit) - when life is not that simple...but the advocates never seem to take a broader view, or their production workflow and deadlines must be very different to mine.

I can't wait for processing power to make high bit, high res files seem like low res thumbs...but while I am stuck with the slow processing on 8 bpc data I can't see high bits being an inducement to greater productivity, let alone output quality (for example, there might be 300 high res images to dust spot, colour correct etc in two to three days - every second counts).

Stephen Marsh.
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Old 01-06-2003, 05:00 PM
john_opitz john_opitz is offline
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There's a sample chapter from Dan Margulis on this subject.Chapter 15

He even has the original files(on the cd) with the curves he applied to them.

John
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Old 06-04-2003, 11:22 PM
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garfield garfield is offline
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so you mean that scanning at 48 bits color will turn it into 16 bits image but why is it when its at 16 bits i cant apply any filter to it? I have to change it to 8 bits? Is this a glitch? is it better to scan at 48 bits rather than 24 bits? Thanks for reading my post
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Old 06-05-2003, 12:19 AM
john_opitz john_opitz is offline
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<<so you mean that scanning at 48 bits color will turn it into 16 bits image but why is it when its at 16 bits i cant apply any filter to it?>>

Some image-editing programs do not fully support 16 bit(high bit) editing.

<< I have to change it to 8 bits?>>

Yes......There is another way to edit 16 bit without converting to 8 bit. But the time and work that is involved does not warrant it(quality wise). ie.... selecting and pasting between documents.


<<is it better to scan at 48 bits rather than 24 bits?>>

If your scanner can give it to you, go for it. Otherwise, it "does not "make a world of difference. Or, as some 16 bit die hards use to say "night and day difference". Then convert to 8 bit for P.S.


John
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  #8  
Old 06-06-2003, 10:37 PM
Stephen M Stephen M is offline
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I generally agree with John.

High bit is also only for flat images at this time, but many folk would like layered support (including me). To me layers are more important than high bits. But give me both and I am happy. <g> Even the new tool from Binuscan, PhotoRetouchPro - which works in high bit mode...does not offer layers - it uses brushes.

At this point in time, high bit processing is very memory intensive and tool support is limited. It takes a lot of time when there is often little perceived visual quality payback for the investment.

It depends on the version of Photoshop, v5.x had no native support for high bit filtering, but with third party support some basic filtering of high bit data is possible (there is even a freeware convolution plug that has high bit support). Photoshop 6 and higher have limited high bit support of some plugs and filters.

Often there is no appreciable visible quality difference between regular and high bit filtering, but with some large gaussian blurs the high bit operation can be a bit smoother in some cases. But to some folk the data is just as critical as visible results, these people often prefer high bit processing.

There should not be any significant speed difference between a high bit and regular bit scan, apart from the file writing time. One would hope that the scanner always scans at the highest bit rate and samples down when a lower output is requested. If performing scanner edits, it would be hoped that these are internally performed at the highest bit rate of the scanner as well.

What Photoshop 5.x or higher can do which scanners often do not is add minor stochastic noise to the high bit to low bit transform. This dither noise which is not really noticeable can add to file size but it can also be of help in breaking up banding or posterization and can be a good thing at times. So for some users it is a very good thing to scan in high bit even if they do not want it and to switch bit depths in Photoshop so that statistical dithered noise is added to the image.

This is not to be confused with the Photoshop colour settings advanced option for dithered noise in regular 8 bpc images - with high bit there is no option and the dither is always on.

Dan Margulis, a noted high bit work-flow critic even changed his viewpoint after some colour scans that were converted to 8 bpc in the scanner were poor after edits, while a high bit converted to regular bit in Photoshop and then edited the same was superior. It appears that the high bit to reg bit dither was the key difference.

Stephen Marsh.
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  #9  
Old 02-20-2004, 05:54 PM
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Markendorf Markendorf is offline
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Exclamation

Hi folks, greetings from Rio de Janeiro- Brasil.

I would like to add some points.

In my experience, if I have the 16 bit version I could extract many details in shadows and bring evem more in high lights.

Many 16 bit files from many and many manufacters are not really 16 bit, but 10/12 or evem 14. PS will "convert" to 16 bit mode and until version 7 will occurr a "quantization error" just because PS use only 15 bit's and take the 1 bit for some task that I can't remember.

Mr. Dan Marguillis are right when talk about the quality in final output BUT, in Imput side I really belive and see many improvements using 16 bit data for very first adjustments. My enviroment are big Add Agency and very pick art directors which would like to change the day light room to night or something else.

Excuse me for my poor english I'm still learning.
Regards,

Adriano
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  #10  
Old 02-20-2004, 06:11 PM
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Doug Nelson Doug Nelson is offline
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Now that Photoshop CS offers broad 16-bit support I rarely leave that mode if given a choice. Layers works fine in 16bit mode.

Look at it this way: if you lose one tone in an 8bit image, you've lost 1/256th of the available tones. If you lose one tone in a 16bit image, it's only 1/65536th of the available tones. In mild retouching this is perhaps trivial, but in restoration every single tone is precious.

I honestly don't understand why there is even a debate. If anyone even pauses to do the math to determine if it's worth the extra hd space, they have something other than image quality as their first priority.
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