Digital versus contact print comparison

[Doug Dolde]

Chris-

Dan Burkholder has a book called "Making Digital Negatives for Contact Printing". Might be worth checking out.

www.danburkholder.com/Pages/main_pages/book_info_main_page1.htm

[paulr]

"The first is, can you make a print that 's indistinguishable from a contact print using these other methods. I think the answer is no. "

I'd certainly agree with that. I don't think it's often possible to make any one thing indistinguishable from any other thing. But that's not usually the point, unless you have something you've done already and feel compelled to match it ... not the case here.

"The second question is, which of these alternative methods will be subjectively most pleasing for Chris's purposes. That question I can't answer."

Nor can I, but I suspect the first question is, will the easy way give results that are pleasing for his purposes? If so, that removes the need to do it the difficult, epensive way. Both methods are flexible enough to produce such a wide range of results. A lot will come down to the quality of the inkjet printer ... if it has the resolution (and freedom from visible dots) needed to give the right level of quality. I suspect it does, based on what I've seen, but only experimenting will tell.

As far as how much resolution it takes to match the visible detail of a contact print, I find you need less than you might think. The very finest detail I've been able to make out in any of my contact prints, in unusually high contrast areas, has been 7 lp/mm. In areas of more normal contrast it's 5 lp/mm. By far the most important thing is the level of contrast maintained in the 1 to 5 lp/mm range. Resolution beyond that means nothing unless you're looking at the print with a loupe.

for what it's worth, my eyes are proably above average for this kind of thing ... no glasses, and I can read the Condensed Oxford English Dictionary pretty comfortably without the magnifying glass.

7 lp/mm is probably achievable with good fidelity and without aliasing at 400 to 450 pixels per inch ... which is possibly part of why Chris finds contact prints to look better than 360 ppi epson prints (the test would be if prints made with a small format epson using the 720 ppi driver look signinficantly better). It's also possible that trying to create the full gammut of colors and tones with 6 to 8 inks, and whatever stochastic algorhythm is available at 2880 dots per inch, just isn't capable of fooling the eye into seeing perfect smoothness. In the world of black and white, 4 monochrome inks and the same kind of printer seem to be able to do this, but I don't know about color.

[David Luttmann]

Paul,

That echoes my tests with the Lightjet at the 402 dpi setting from film scans. At 402 dpi, approx resolution is just shy of 7 line pairs at normal contrast. It can approach 9 lines pairs on higher contrast targets. Yes, it can measure better if you're photographing air force test charts....but I don't see many charts in photography magazines or galleries.

This is one of those times where the numbers are much lower than many people think. We quite often hear about figures of 30 to 50 line pairs for LF contact prints which is rubbish considering the paper cannot maintain that level of detail nor can the eye discern it without a loupe. More wishful thinking on the part of the printer than anything!

Cheers,

[neil poulsen]

Dan's book doesn't really focus on color. I just took his workshop, and he focuses primarily on black and white, pt/pd, or pt/pd on pigment using a black and white digital negative. The color aspect of his work (pt/pd on pigment) is unique and beautiful, but nothing like the print for which you're aiming.

To me, the look of contact printing comes as much from not using an enlarger as it does from the excellent detail inherent in a contact print, and from the fact that one's using silver based materials. Using an enlarger introduces flair and probably other idiosynchrasies that give a print that non-contact printed look. That's our frame of reference when we view a contact print, how it compares to an enlarged print.

I would want to compare whatever I did with a straight Lightjet or Lambda print from a 1 gigabyte scan. Use the internegative and do the contact print for one print, and then compare. The Lambda or Lightjet also sidesteps the enlarging process and might have a "contact print" look.

If you were targeting a black and white rendering of your films, then Dan's book could be especially appropriate. For example, one could get image setter digital negatives at higher resolution and contact print those.

[sanking]

"As far as how much resolution it takes to match the visible detail of a contact print, I find you need less than you might think. The very finest detail I've been able to make out in any of my contact prints, in unusually high contrast areas, has been 7 lp/mm. In areas of more normal contrast it's 5 lp/mm. By far the most important thing is the level of contrast maintained in the 1 to 5 lp/mm range. Resolution beyond that means nothing unless you're looking at the print with a loupe. "

I don't agree. Studies on the limits of human vision show that at optimumviewing distance of about ten inches the eye is capable of perceiving differences of up to 25 lppm. The eye is not capable of consistently resolving 25 lppm, but it will perceive a difference in sharpness beteen 5 lppm and 25 lppm.

The question should probably be this. What is the worst (in terms of the lowest resolution) image that can be tolerated. In that respect I would agree tht 5-7 lppm is the low limit.

The very best digital prints are limited to a maximum resolution of 7-9 lppm. Contact prints from LF and ULF negatives on suitable papers, AZO for example, are capable of resolution values of 25 lppm and even higher. If you were to compare prints of equal size, one made from a scan of an 8X20 negative and printed on a inkjet printer, the other a direct contact print on AZO, there is no question but that most people would perceive greater sharpness in the AZO print. On the other hand, if one were printing with Pt./Pd. on the art papers we typicaly use with this process, there would likely be no perceived difference in sharpness because the paper itself is the limit to resolution and perceived sharpness.

[sanking]

"This is one of those times where the numbers are much lower than many people think. We quite often hear about figures of 30 to 50 line pairs for LF contact prints which is rubbish considering the paper cannot maintain that level of detail nor can the eye discern it without a loupe. More wishful thinking on the part of the printer than anything! "

Not correct. Ctein tested this and found that some papers are capable of resolution values of up to 125 lppm, which is well beyond the capability of most pictorial films.

[David Luttmann]

Sandy,

I have yet to see any paper capable of those resolutions, unless you spend your days photographing high contrast test charts.....which is not what you'd achieve under standard photographic contrast.

And while the eye may be able to discern the difference between 5 lp and 25 lp....it won't do so at a viewing distance of 18" to 2 feet.....which is about where people woould view a print in the 30" or so size......or are we talking about viewing images at a gallery thru a loupe? I must admit that I don't carry a loupe to look at photos so I can't be much help there.

Truly, if you are achieving 9 line pairs at 11x14 or 16x20, you have a rzor sharp print that needs no apologies.

[Oren Grad]

Sandy - we've had this discussion before. Paulr and Dave don't buy Ctein's results and his interpretation of them. Although I think Ctein's right, I can understand the skepticism - it's actually very difficult to think of an experiment that can be done without exotic equipment that will demonstrate directly, rather than by inference from disparate bits of evidence, not only that contact prints look different from other types, but that information in the 10-30 lp/mm range is specifically what's responsible for the difference.

[sanking]

"And while the eye may be able to discern the difference between 5 lp and 25 lp....it won't do so at a viewing distance of 18" to 2 feet.....which is about where people woould view a print in the 30" or so size......or are we talking about viewing images at a gallery thru a loupe? I must admit that I don't carry a loupe to look at photos so I can't be much help there.

First, I am not talking about looking at prints with a loupe, but at a distance of ten inches, a distance that many people would consider a reasonable distance for critical viewing an 8X10" contact print. At that distance most people will indeed perceive a difference in sharpness between 10 lppm and 30 lppm. And there is absolutely no trouble at all in getting 30 lppm is on a smooth photographic surface from an 8X10 contact print, assuming good technique in focusing and exposing the negative, and further assuming that you don't stop down so much that the lens becomes diffraction limted at less than 30 lppm. That figure, by the way, is about f/64 for a contact print.

Whether or not it is possible to actually get 125 lppm on a print I don't know, and it is probably irrevelant anyway since for all practical purposes that kind of resolution is impossible to get on film. But 30 lppm is a piece of cake.

[paulr]

"I don't agree. Studies on the limits of human vision show that at optimumviewing distance of about ten inches the eye is capable of perceiving differences of up to 25 lppm. The eye is not capable of consistently resolving 25 lppm, but it will perceive a difference in sharpness beteen 5 lppm and 25 lppm."

Can you cite this research? I've looked at a pile of research and it all contradicts this. So does the research that's taken as gospel by the engineers at the lens companies. I've had long conversations about this with tech reps at Schneider.

According to everything I've seen, the maximum theoretical frequency that the eye can discern is about 14 lp/mm (at the 10" focusing distance you describe). This is based purely on the spacing of the rods and cones in the retina, and presumes all other conditions are perfect ... perfect optics of the eye (which no one has), and a high-contrast, backlit slit target whose range of light to dark is measured in the optimum range for human vision.

With actual eyes and their more humble optical abilities, but still with high contrast, backlit test targets, people can discern about 11 lp/mm.

With high contrast detail in actual photographs, the limit tends to be closer to 7 lp/mm.

With medium contrast detail in actual photographs, it's more like 5 lp/mm.

This surprises a lot of people, because these number sound so small. But if you actually measure the size of details on your prints, it will make sense. It's easy to do if you have good scans of the negatives. Look at a contact print, and identify the smallest details that you can see. Then go into photoshop, look at the scan, and measure. A tenth of a milimeter is actually really, really small.

None of this has anything to do with aliasing, or rendering of smooth tones ... just with discerning fine details and textures.