Scanning Black and White Film as Negative or Positive?

[GraemeMitchell]

So all theory and staring at the histogram aside, the idea is to get the best file you can - best meaning the one closest to the way you want it to print - during the scanning phase. It's what that software is written for...albeit some better than others. Ditto for processing out RAW files, best to get it as close as possible to done in your RAW process.

Photoshop isn't meant for inversions and big tone and/or color shifts...not technically at least. Watch the histogram, anytime you start to see it break up it's destructing the tone/color integrity of the file. A little is okay, a lot and you'll see it in print.

 

[Alan Klein]

Chuck: Thanks for your expansive explanation. It seems initially logical that by adjusting the black and white points inwards, the gradation of tones will be greater. You'll be expanding the range from 0-165 to 0-255. I also read somewhere that data is greater more at one end of the range than at the other which is why some people expose to the right. However that's in a camera where you can change exposure. In my scanner at least, the scan falls within the normal range and cannot be clipped because of the limits of the dMax of the scanner.

The question I'm wondering is first how do we know that the scanner is not just adjusting the black and white points, either automatically or manually as selected, after the scan's data is captured "flat". Not before or during the scan. In effect, the data at the end of the scan for the range of that particular photo is the same whether white and black points were adjusted or not. It's just that the scanner program applied a level adjustment to the data after the scan is done and produced the full 0-255 range of data for the photo portion. But the data for the photo range of 0-165 as in my example contains the same data at the end of the scan regardless of the black and white point setting.

If that's the case, than the final outcome would be effectively the same as applying levels in Photoshop afterwards.

Do you know of any educational, professional or trade referecne that would explain these processes? Thnaks Alan.

 

[artobest]

Alan, I'm pretty sure the results are the same whether you do the levels adjustment in the scanning software or later, in PS. The option is there in the scanning software for convenience, so you can get a decent scan without resort to external software.

Two caveats: this applies only if you scan as positive (ie, without the scanner making a TRC adjustment to the scanned data), and secondly, you need to scan in 16-bits to ensure the final adjustment is as precise as it can be.

 

[chuck94022]

Chuck: Thanks for your expansive explanation. It seems initially logical that by adjusting the black and white points inwards, the gradation of tones will be greater. You'll be expanding the range from 0-165 to 0-255. I also read somewhere that data is greater more at one end of the range than at the other which is why some people expose to the right. However that's in a camera where you can change exposure. In my scanner at least, the scan falls within the normal range and cannot be clipped because of the limits of the dMax of the scanner.

This issue is the same with cameras or scanners and has to do with the nature of CCD representation of logarithmic light intensity (optical "stops" are logarithmic) with linear values. This is unrelated to clipping or the ability to change exposure.

The question I'm wondering is first how do we know that the scanner is not just adjusting the black and white points, either automatically or manually as selected, after the scan's data is captured "flat". Not before or during the scan. In effect, the data at the end of the scan for the range of that particular photo is the same whether white and black points were adjusted or not. It's just that the scanner program applied a level adjustment to the data after the scan is done and produced the full 0-255 range of data for the photo portion.

Why don't you do a test and post the results? Peek at individual pixels in a small sample using your scanner with various adjustments?

But the data for the photo range of 0-165 as in my example contains the same data at the end of the scan regardless of the black and white point setting.

Really? Did you test this theory? See above suggestion.

If that's the case, than the final outcome would be effectively the same as applying levels in Photoshop afterwards.

Again, do the test yourself on a small sample - for example, a small part of a dark area of one of your images. Compare the pixel values that result individually. You will answer your own question.

Do you know of any educational, professional or trade referecne that would explain these processes?

Pellicle's blog posts have a couple of great links, and I'm sure you'll find many more with Google. Tip: try "linear CCD"



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I am here: http://maps.google.com/maps?ll=40.029179,116.510999

 

[Alan Klein]

Michael: Well I took your suggestion and compared at about 300% and up. The images that were scanned flat and adjusted in Photoshop Elements 8 afterwards do have more pixelations especially in the flat areas. It's very obvious. Those areas are much smoother where Auto adjustments were applied during the scan. You can see it both in light as well as dark areas. That shoots down my theory and tells me to only bother scanning with initial level adjustments in the scanner.

Now, I have to play with Manual vs. Auto to see if Manual point adjustments will work better for me than Auto.

Thanks for your input and kudos to Pellicle as well. Alan.

 

[chuck94022]

This issue is the same with cameras or scanners and has to do with the nature of CCD representation of logarithmic light intensity (optical "stops" are logarithmic) with linear values. This is unrelated to clipping or the ability to change exposure.

I should have more specifically said that the issue is the same with digital cameras (and integer linear values).

 

[Alan Klein]

Just a clarification regarding Artobest's post. The pictures I compared in my last post were scanned at 8 bit and were negative film (Portra 400). I set the V600 scanner for negative film to match the actual film.

 

[Alan Klein]

Sorry Chuck for calling you Michael.