Chuck: Thanks for your thoughts. I've compared both my scans where one scan was scanned flat and was post processing in Auto Levels in PSE-8. It matched the image results in Auto set before the scan. So that test didn't seem to prove that one way is superior to the other. However, I might be fooled because I'm depending on my eyes in a small image on a computer screen.
Here are questions I asked previously but didn't get responses. Maybe you can answer them. I'm trying to understand how the scanner creates its image scan file. That may answer the question of which way is better.
1. If I have a film that has a histogram range of 0-165, will I get more data in the scan file to work on if I move the white point in the scanner from 255 to 165 rather than leaving it "flat" and scanning the full 0-255? In other words, will the data file at the end of the scan have more data representing the 0-165 then the same 0-165 area if I scanned "flat" from 0-255?
2. How could I measure the difference between moving it and scanning "flat" assuming pixel count and file size does not provide that information as someone stated above?
Thanks. Alan
Hi Alan,
I'll try to answer.
QUESTION 1
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No, you will not get more data. In this answer I am assuming by "more" you mean it in the obvious sense: more pixels (or in computer jargon, more bytes) of data. Instead, the software will be able to map the 0-255 to finer changes in the raw measurements. In other words, a change of 1, say from 90 to 91 in value will represent a smaller change in tone.
This would be good, if the software didn't also apply a bias (or as Pellicle states, "change the 'curve'") at the same time, which is the fundamental issue Pellicle is raising. This bias means that the amount of change in tone between, say, value 90 and value 91 is not the same as the amount of change in tone between value 150 and 151, because the software is applying an additional function to the result spreading the tones in the range of 0-165 to the values 0-255. It is doing this non-linearly, or putting it in simple terms, applying a bias to the values.
You cannot change this back in Photoshop - this mathematical function cannot be reversed. Pellicle gets deeper into the reason for this, but it boils down to this: the scanner sees extremely fine changes in tone, which it maps to a (relatively speaking) very course set of fixed values (0-255 when using 8 bits). This process (in the software) is taking a floating point number between 0 and 1 from the CCD hardware (say, .25598337221) and mapping that to a fixed integer between 0 and 255 (say, 50). The next value from the CCD might be .25648825443, which might also get mapped to 50, unless a bias is being applied, in which case it could get mapped to 51.
Put yet another way, the scanner's software is automatically compressing or expanding certain value ranges outside your control when it automatically introduces a bias function.
Since Photoshop (or whatever editor you use) doesn't know it is getting values that have been biased by a function, you cannot easily (if at all) use the curves in Photoshop to counteract the bias that was done by the scanner. It just complicates things.
However, all that said, it is entirely possible that the best scan from a particular image might come from a scan of the negative, with a bias curve automatically applied. It all depends on the image. Converting from raw CCD data (which is basically analog), to a set of discrete digital values is not a process where one size fits all. That is the issue Pellicle and others have with relying on the automation in the scanner. In many cases, the math is not a good fit for the data, and the scan suffers as a result. But note, many other times, the automation *does* work just fine. And that is why it is there.
QUESTION 2
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The measure you seek can only be done by visually comparing the result of the scan with the actual negative. You can't put a number on it. For example, look at areas of the sky, or shadows. Do you see excessive noise (grainy when it shouldn't be, or blotchy when it shouldn't be)? This kind of problem can't be seen in a histogram or in file sizes, because it represents small errors in the value of single points in the image. Pellicle's workflow attempts to assure that the quality - and I emphasize quality, meaning accuracy - of the individual pixel values loaded into Photoshop is as high and usable as possible.
You might find that for an image you scanned with the automation in the scanner, it came out just fine - spectacular. Great, you win! You may find at other times that the image just doesn't seem as good as it could be, when comparing it to the negative under a loupe. In that case, you might try Pellicle's approach, to see if maybe you can squeeze out a better result by taking more control over the scan.
Also, note, and this is important: it is highly unlikely that you will be able to tell much of a difference in any of the above at web resolution. To see the issues, you need to look at your images full size, not scaled down to fit the screen (in Photoshop, choose "Actual Pixels" in the view menu). If you never intend to show your images at the full scanned size, but instead at greatly reduced web size (for flickr, facebook, etc.) most of these issues are moot. Scan in the easiest way that works for you, the results should be perfectly fine, except for tweaking colors a bit to make them look good enough.
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By the way, in their defense, I think Pellicle, et. al. did respond to these questions, but the language they are using, relating to integer math, curves, etc. may not be something you are familiar with. I hope the above helps, regardless. I also think the discussion about whether the scanner speeds up or slows down to accomplish all it does is a distraction. What matters is what it produces, and how well you can use that result.