Scanner comparisson page and drum scan limits?

[Tyler Boley]

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

Lenny, two givens-

1) "some serious compression of tones... ...happens on occasion"
2) the Photoshop curves tool has control points in increments of 256, both
in and out, no matter the number of levels in the
file.

One has little, if anything, to do with the other.

another two-
1) world views
2) facts

Again, one has little, if anything, to do with the other.

As a note of interest perhaps, your multi K setups will indeed
differentiate between more than 256 levels of gray (given enough room on
the paper), unfortunately StudioPrint converts to 8 bit on the fly behind
your back, before continuing on with the magic it does. Don't ask me to
write the novel required to explain how I arrived at that. So, there is
one bottleneck, though I don't think the problem you mention is at that
point. Still, I'm in agreement that there should be no downscaling of
levels of gray anywhere in the data path if at all possible, but PS tools are a different issue.

Peter, I had no idea you were referring to LAB, that's an entirely
different can of worms, and you are right about the increments of control
points available with it in PS.
At risk of offending you as you may be well aware already, there are other
perhaps more useful tools. Despite it's silly Tron like interface, i1
Share (free) will let you measure in accurate LAB values and tell you the
equivalent RGB value in any selected working space, for example.
Tyler

[Lenny Eiger]

Lenny, two givens-

1) "some serious compression of tones... ...happens on occasion"
2) the Photoshop curves tool has control points in increments of 256, both
in and out, no matter the number of levels in the
file.

As a note of interest perhaps, your multi K setups will indeed
differentiate between more than 256 levels of gray (given enough room on
the paper), unfortunately StudioPrint converts to 8 bit on the fly behind
your back, before continuing on with the magic it does. Don't ask me to
write the novel required to explain how I arrived at that. So, there is
one bottleneck, though I don't think the problem you mention is at that
point. Still, I'm in agreement that there should be no downscaling of
levels of gray anywhere in the data path if at all possible, but PS tools are a different issue.

Tyler

There's part of this that is just interim, or incomplete thinking. I've been working for a long time to get to a fully textured appearance. I have been successful at getting there with an 8x10 camera. However, I believe I should be able to get there with a smaller piece of film - at least one as large as 4x5. Somehow it doesn't work that way - at least not yet. There's a smoothness I haven't gotten to. I'm grasping at straws to figure out where the bottleneck is. I have very smooth gray ramps in my environments but the magic is only there with the big camera - at least so far. More testing to come.

I do know that StudioPrint is 8 bit. They just told me, thankfully no novel needed.

My statement about world views had to do with the comment you made about "losing touch with these discussions every day..." It was an attempt at levity.

Lenny

[sanking]

There's part of this that is just interim, or incomplete thinking. I've been working for a long time to get to a fully textured appearance. I have been successful at getting there with an 8x10 camera. However, I believe I should be able to get there with a smaller piece of film - at least one as large as 4x5. Somehow it doesn't work that way - at least not yet. There's a smoothness I haven't gotten to. I'm grasping at straws to figure out where the bottleneck is. I have very smooth gray ramps in my environments but the magic is only there with the big camera - at least so far. More testing to come.

Lenny

Have you ever considered the possibility that the lack of smoothness might be due to the type of scanner you are using? Maybe you should experiment some with one of those inferior flatbeds? Could me that Premier is just looking too deeply into the film and finding things that were never meant to be found.

Sandy

[Tim Povlick]

Have you ever considered the possibility that the lack of smoothness might be due to the type of scanner you are using? Maybe you should experiment some with one of those inferior flatbeds? Could me that Premier is just looking too deeply into the film and finding things that were never meant to be found.

Sandy

Hey Sandy, I think your on to something there. How about a SF plot where a film scanner looks so deeply into the film it can see future events.... Queue the Twilight Zone theme.

---

Well, I am from Earth, although I have been to Mars (PA) to answer some of the previous questions about what planet we (Lenny and I) are from. I won't speak for Lenny on that one.

The comment about the tone curve tool being 0 to 255 is because in 16-bit it's mapping 0 to 255 to 0 to 32768 (thanks to Tyler for point out PS uses 15bits of actual data, confirmed in a PS text I referenced). Therefore if one changes 124 to 125 then this is mapping to 15872 to 16000. One could counter and say "doesn't matter as it gets mapped to 8-bits eventually". If that's your workflow np for me.

One concern I have is the graph is so small when making the adjustments to the curve, it would be real nice if PS allowed one to stretch the window larger. Will I continue to use the curves tool - YES.

_ .. --
Tim

[wfrascher]

[QUOTE=Tim Povlick;626767]

One concern I have is the graph is so small when making the adjustments to the curve, it would be real nice if PS allowed one to stretch the window larger. Will I continue to use the curves tool - YES.
_

Tim, get with some digital astronomers and import your pictures with their programs. They've been able to stretch for more then a decade. I guess to say stretch would be wrong, you can zoom in or out. :-)

[Lenny Eiger]

Have you ever considered the possibility that the lack of smoothness might be due to the type of scanner you are using? Maybe you should experiment some with one of those inferior flatbeds? Could me that Premier is just looking too deeply into the film and finding things that were never meant to be found.

Sandy

Nice idea but that isn't it. I think its just film real estate. But I also think its how I'm addressing the specific issues....

Lenny

[SCHWARZZEIT]

There's part of this that is just interim, or incomplete thinking. I've been working for a long time to get to a fully textured appearance. I have been successful at getting there with an 8x10 camera. However, I believe I should be able to get there with a smaller piece of film - at least one as large as 4x5. Somehow it doesn't work that way - at least not yet. There's a smoothness I haven't gotten to. I'm grasping at straws to figure out where the bottleneck is. I have very smooth gray ramps in my environments but the magic is only there with the big camera - at least so far. More testing to come.

I think you're right that the issue you have is about film real estate. If you have a certain print size in mind e.g. 40x50" the grain structure of your 4x5" film going trough a 10-12x magnification while it's only 5-6x for an 8x10" sheet.
It depends on the film you're using but even on modern flat crystal emulsion films you can already perceive a loss in smoothness when enlarged ten times. The grain already interferes with the texture of your image.

Which type of film have you used for your comparisons so far?

-Dominique

[Lenny Eiger]

I think you're right that the issue you have is about film real estate. If you have a certain print size in mind e.g. 40x50" the grain structure of your 4x5" film going trough a 10-12x magnification while it's only 5-6x for an 8x10" sheet.
It depends on the film you're using but even on modern flat crystal emulsion films you can already perceive a loss in smoothness when enlarged ten times. The grain already interferes with the texture of your image.

Which type of film have you used for your comparisons so far?

-Dominique

Dominique,
I am currently using Delta, and on occasion TMY-2 (for low light). It isn't the film, however, grain patterns or scanning sharp.

Here's my example: let's say you have a telephone pole in your image. It's one of those that has a seemingly endless number of shades of brown from the aging of its creosote coating (I presume they do this, or did, in the EU, and that you have these objects over there).

Let's also suggest that on a 4x5 piece of film you can take a square sample (crop) that will represent the width of this telephone pole and that with a 4x5 the width and height of this sample is .64 centimeters, or close to 1/4 of an inch.

Resolution is not the issue here. The edge of the pole will be sharp in all med-large formats, at least. However, if you compare the tonal reproduction capacity of this 4x5 vs the capacity of an 8x10, the larger film will reproduce the same square of the image in 2.54 centimeters, or a full square inch. There is far more tonal information in an inch of film vs a 1/4 of an inch.

I go over and over this in my mind. I think I am almost there, my next experiment should provide a path to see what exactly is and is not possible between the two formats with identical (both Rodenstock Apo-sironar-S lenses, both normal for the format, and matching film and development, with an appropriate subject that is tonally rich.

Lenny

[sanking]

Dominique,

Let's also suggest that on a 4x5 piece of film you can take a square sample (crop) that will represent the width of this telephone pole and that with a 4x5 the width and height of this sample is .64 centimeters, or close to 1/4 of an inch.

Resolution is not the issue here. The edge of the pole will be sharp in all med-large formats, at least. However, if you compare the tonal reproduction capacity of this 4x5 vs the capacity of an 8x10, the larger film will reproduce the same square of the image in 2.54 centimeters, or a full square inch. There is far more tonal information in an inch of film vs a 1/4 of an inch.

Lenny

My experience is that all things being image quality will always be better with the larger format when comparing film of the same type in 8X10, 4X5 or MF. So if you are comparing the same file in 8X10 and 4X5 it is kind of a no brainer that the 8X10 image is going to look better because of the smooth tones, certainly in any print over 16X20 and perhaps even at that size depending on how close you put your nose to the print. And that would be true even if the resolution of the 4X5 negative it 2X that of the 8X10 negative because even if you have the same amount of detail the structure of the film will be smoother with 8X10 because of less enlargment.

The only way 4X5 can match 8X10 in image quality (or Mamiya 7 can match 4X5) is by the user of a higher resolution film with finer grain. I know for a fact, at least to my own satisfaction, that Mamiya 7 negatives on Fuji Acros, if well exposed and developed, equal or beat print quality from 4X5 Tri-X or TMY-2 negatives. Naturally we are talking about an apples to apples comparison where both cameras are used on a tripod, at a shutter speed that does not cause vibration, and at an optimum aperture.

The characteristics of B&W film are fairly straight forward. There is grain, resolution, dynamic range, curve type and spectral sensitivity. Did I miss something? Image quality itself does not result from any one of these characteristics but from all of them, and how the negatives matches the printing process. I think often people lose their way because they place too much emphasis on just one or two aspects of image quality and lose sight of the whole.

Sandy King

[rdenney]

I'd like to describe something in analogue terms that I think we may miss in these discussions, and as a test of my own thinking.

At various points in the discussion, the notion of a chain has been mentioned, with resolution being determined by the weakest link in the chain. But I don't think a chain is a good analogy. The chain concept suggests that if any link is strong enough, it has the same effect as if it is infinitely strong. If the resolution of, say, the lens is greater than the film, then the lens no longer has any effect on what we see. I don't think that is correct.

The point behind thinking in terms of modulation transfer is to think of waveforms. The scene presents a pattern of waveforms, some of which have, from the perspective of the camera location, infinitely sharp edges, and some of which have gradations.

A lens always renders the scene with gradations--if we look at a small enough piece of the scene that it projects. A lens imparts its own look in the way that it converts the scene's edges and gradations into gradations that do or don't appear to be sharp (even for scenery elements that are in exact focus, which, of course, most aren't). Lines per millimeter is a gross way of measuring this effect, in that it only considers sharp scenery elements. MTF is much better, because it looks at the way the lens modulates the edges and gradations of the scene at different spatial frequencies. But at high enough spatial frequencies, the MTF is always less than 100%--there is a point at which the lens will turn any sharp detail into a smooth gradation.

The film has a completely different way of integrating the information. It imposes its own patterns on the scene, with its own modulation effects. How it does so is what makes each film different, and, from an artistic perspective, this leads to photographers having preferences. Some tonal gradations imposed by the lens may be rendered as a sharp edge again by the film, if it lacks the ability to render a gradation at that spatial resolution. A film may render a straight detail projected by the lens as a ragged edge, where the raggedness of the edge (if it is fine enough) creates the impression of a gradation, and in so doing might add to or obscure the gradation projected by the lens.

If we enlarge, then the enlarger lens and the enlarging paper will each put their characteristic stamp on the result.

It's not a chain. Rather, it's a series of transparent overlays, with each imposing a different way of representing fine detail.

Scanning film also imposes a different pattern on the image. The film's ragged pattern imposed on the gradations projected by the lens will get sliced in a regular grid pattern of samples, and each sample will integrate whatever it sees in that sample. And with many scanners, the samples will overlap, so that each sample will integrate the content of that sample, plus some information from the film in neighboring samples. And scanners that use CCD arrays will scan different colors spatially offset from one another. In that way, the scanner also imposes a modulation by superposing it's sensor frequency and color array on top of the modulation frequencies that are on the film.

So, we have a superposition of wave patterns--the scene, the lens, the film, and the scanner. Each works at a different frequency, and each does different things at different frequencies. Only when one step in the process is grossly less able to handle important frequencies than the others does it become dominant. If one step has much greater resolution than the others, then it has less effect on the integrated total.

In practical terms, if our goal is to render the integrated image as recorded on the film with no further effect, the scanner must be able to see finely enough to describe the grain shapes. So, a film that can resolve x lines/mm might need to be scanned at 10x or 100x to render those grains accurately. Any less will cause the result to see the modulation effects of the scanner, and any less will cause a change in the way gradations are rendered in fine detail.

If our goal is to produce pleasing prints, then we can make use of or work around the modulation effects of the scanner. If that is our goal, then we can determine scanning resolution on the basis of what produces pleasing results for the prints we will make. The rendering of fine detail in a print will be the integrated or superposed modulation of the scene, the lens, the film, and the scanner, with none imposing such an effect as to undermine our aesthetic intent. This is the situation that leads to the chain analogy, but for one of those steps to dominate the result negatively, its modulation has to be a gross effect compared to the fine effects of the other steps. So, again, a scanner might have to have ten times the effect on a given detail than the lens for it to dominate the final result.

A step cannot dominate the result by being too finely resolved. If we modulate accurately at finer levels, the gradations at grosser levels will be accurate. The finer the spatial resolution, the fewer shades of gray are needed to still be accurate at much lower spatial resolutions. There is a spatial resolution where we can provide only binary black or white and still end up with a completely smooth gray scale at lower resolutions. If we get banding at lower levels, it is because our data has been represented at lower resolution, not lower bit depth. But I'm not talking about pixel counts, but rather clusters of pixels all the same color--this is what we call banding or posterization--, which is another way of lowering spatial resolution. Given that we can't practically scan at 100 or 1000 times what we intend on a print in terms of spatial resolution, we end up worrying about accurately integrating larger samples. Our samples are so large that we are forced to represent them as accurate integrations of what they are sampling.

So, for low-res scanners, we want lots of color depth and accurate sampling. The higher the resolution of the scanner, the less accurate each sample needs to be.

I suspect a PMT drum scanner outperforms flatbeds more because of its very high resolution than because of its accuracy for each sample. It may have resolution some large multiple of other steps in the process, but by so doing, improves accuracy without needing each sample to be more accurate.

An Epson flatbed, on the other hand, has low spatial resolution similar to or lower than other steps in the process. Thus, it must represent each sample accurately. But it does not--there is still too much bleeding from one sample to the next, or from one color to the next within the CCD pattern. A Nikon film scanner probably does not have better CCD technology than the Epson, but performs better in terms of broad tonality because of the higher resolution. I know this is weird thinking, but I believe the science supports it.

So, before we can ask about limits, it seems to me we need to set standards for the result we want. If we want everything a given film offers with no influence from scanning, I think we will need extremely high scanning resolution, perhaps one or two orders of magnitude greater than what we expect from the film. The greater the spatial resolution, the less we have to worry about accuracy, it seems to me. The less the spatial resolution, the more we have to worry about accuracy and color depth.

Rick "whose Epson isn't quite accurate enough for enlargements greater than about 4x" Denney