Scanner comparisson page and drum scan limits?

[Tim Povlick]

Tim,
I am curious myself. According to latest Photoshop we are in 16 bit - so there should be 65,536 possibilities, if my math is correct. However, when we move a curve up and down, we only have 0-255 as choices. This would appear quite sledge-hammer-ish as a tool. In terms of b&w, I also don't think my printer can separate out that many tones. My gray ramps are perfectly smooth, but the resolution is low - 1440x1440. So if I only have the tones that can be generated with that resolution, I believe its quite limited. I don't know what the number would be... do you?

Lenny

Hi Lenny,

Your math is correct, there are 64k possibilities (separations?). As to the photoshop, I think if you are in 16-bit mode the tone curve is presented to the user as 0 to 255 they are expanding it to 16-bit internally and I see your point that in so doing one has only a crude control over the curve that is 16-bit with an 8-bit control. If they allowed user input of a curve one would generate the desired curve to perfection, but that would be a 64k table to fill. Ouch. My only suggestion is be very precise with the curve tool in PS. Maybe someone can suggest a better suggestion.

I checked the Hamamatsu site concerning the PMT's spec's. I don't have the PMT number used in our Premiers but a PMT I looked at had the following features. If one took dark current as a "step" and maximum current as the max limit as the number of steps, then you ended up with a PMT that had 20,000 steps. Interesting result (matched Haddon's number). A more interesting was take the minimal value the PMT could sense and use that as step size. To my way of thinking this is the proper value to use. The PMT then had 6,000,000 steps. In otherwords, a 22-bit DAC could realistically be used to capture a color channel. That would yield 66-bit RGB. No way to print that :-)

_ .. --
Tim

[SCHWARZZEIT]

They have told me its a 16 bit. Must be the effects of rounding numbers up and down... for discussion.

Lenny, I confused the number of values in 14 bit and 16 bit. My mistake! 64K values is of course correct for 16 bit. So a 16 bit ADC is sufficient for the 20K separations of the PMT.

Regarding raw vs adjusted at scanner scans- one thing the software does (DPL) does that's great is that they have a "CMS" file attached to each scan. This gets loaded into the scanner at scan time and adjusts the range of the scanner. This is very different from doing a raw scan, like most scan software does. The pro version allows you to create your own cms file/profile for each image. It's not needed for most chromes, and only some color negs, but its great for b&w negs. It's like having a different scanner for each image. At least that's what I've been told and the premise I am working on. It appears to be working that way, but there's plenty I don't know...

Ok, I think I get how the CMS files work. On my ICG scanner there are basically just two hardware modes that define the range. One is called standard range which is good for all but very dense negatives and the other is called extended range where the full 4D+ range of the scanner engine is used. The hardware difference between these modes is that they calibrate to different values. Or in other words there's a difference in gain. I think the CMS files work similarly on your Premier but you can adjust them precisely to the density range of your original. Whether you really see a difference in the final print file is a different matter.

As to the photoshop, I think if you are in 16-bit mode the tone curve is presented to the user as 0 to 255 they are expanding it to 16-bit internally and I see your point that in so doing one has only a crude control over the curve that is 16-bit with an 8-bit control. If they allowed user input of a curve one would generate the desired curve to perfection, but that would be a 64k table to fill. Ouch. My only suggestion is be very precise with the curve tool in PS. Maybe someone can suggest a better suggestion.

On an 8-bit curve in PS you may be able to see the change of single values. On a 16-bit curve smaller adjustments would be invisible when the changes are lost on its transfer to the display device. If however you feel that you need finer adjustments on your curves you may reduce the opacity of each curve layer or fade the adjustment after applying the curve directly to the image.

-Dominique

[Tyler Boley]

really? You guys really find moving mid tone value, oh say, 124, up to 125 too sledge-hammerish? You really want a curve tool that has tens of thousands of steps because 124 to 125 was just overwhelming? You put those two prints next to each other and the difference is not only visible but far to great?
Man, I'm losing touch with these discussions more and more each day...
Tyler

[sanking]

really? You guys really find moving mid tone value, oh say, 124, up to 125 too sledge-hammerish? You really want a curve tool that has tens of thousands of steps because 124 to 125 was just overwhelming? You put those two prints next to each other and the difference is not only visible but far to great?
Man, I'm losing touch with these discussions more and more each day...
Tyler

I agree with you Tyler. Sounds like these guys are working on some planet other than Earth because they are discussing subtleties of tonal values way beyond the capability of the human eye.

Sandy King

[Peter De Smidt]

Recently, my neighbor asked me to photograph his house and then use Photoshop to colorize sections of it so that he could determine a paint choice. He gave me some paint samples to match.

My spectrophotometer reads to tenths, but photoshop curves/readouts are whole digits. Being off by a couple of tenths was clearly visible. Thus, for some things, such as very close tolerance color matching, Photoshop is a bit of a sledgehammer. I've never found this to be a problem doing regular printing.

[Tyler Boley]

by the way, "16 bit" Photoshop mode works in 15 bit + 1 unit, 32,769 values per channel.
Tyler

[Bruce Watson]

Really? You guys really find moving mid tone value, oh say, 124, up to 125 too sledge-hammerish? You really want a curve tool that has tens of thousands of steps because 124 to 125 was just overwhelming? You put those two prints next to each other and the difference is not only visible but far too great?

Man, I'm losing touch with these discussions more and more each day...

I promised myself that I wasn't going to add my voice to yet another thread like this (emphasis on another). Oy, failed again. But yeah, what Tyler said.

I would only add that the tones on the print are the result of the entire system, not just photoshop. I wonder how much an effect paper batch variability, ink batch variability, ambient temperature and relative humidity, etc., have on the tones. I suspect it's a significant fraction of the difference between 124-125.

So are you guys making new profiles for every print you make? Sorry, please don't answer that. If you are, I don't want to know.

I'll leave this thread with a story. I seem to remember a story Fred Picker told, went something like this. When he was a hungry young photographer, he worked (apprenticed?) for some excellent darkroom printers. And Fred, being Fred, could be a PITA at times. So one of the experienced old guys challenged him to print as many individual shades of gray as he could. Take as long as he needed, use whatever techniques he liked.

Turns out Fred was able to come up with something like 54 or 55 distinguishable shades of gray. Try as he might, that's where he seemed to top out. This surprised and impressed his teachers, but Fred was usually one to exceed other peoples' expectations, apparently.

My take on this is that the number of tones you can make might be interesting but it's only a small part of what makes a photograph.

[Tyler Boley]

Peter, forgive me but I'm not following... tenths of what? Most Photoshop tonal tools work in 256ths, that won't more than cover your couple of 10ths by orders of magnitude?
Tyler

[Peter De Smidt]

Peter, forgive me but I'm not following... tenths of what? Most Photoshop tonal tools work in 256ths, that won't more than cover your couple of 10ths by orders of magnitude?
Tyler

Sorry, I made a mistake. My spectro reads to hundredths. So for example, one paint chip measured L 95.26, a 0.39, b 1.76, but entering lab numbers in Photoshop is limited to whole numbers. Using L 95, a 0, b 2 did not produce a visually matching color.

[Lenny Eiger]

Guys, before you jump all over everyone-- there is some serious compression of tones that happens on occasion, at least. I'm not sure where exactly it occurs. I assume its in Photoshop, but it could be in the rip. There's a certain effect that I get when I use an 8x10 piece of film that adds an extreme amount of textural quality. I think it should be able to happen at smaller formats, certainly 4x5, given resolution of lenses, excellent film and developers, the best kinds of scanners, etc. All the stuff we all use.

I realize the eyes can only go so far, monitors only os far, etc. I continue to struggle to get more than I am getting from smaller film...

This doesn't have to do with world views...

Lenny