Enlarging: How "Lossy"

[Ken Lee]

When we enlarge an image with a high-quality enlarging lens, how much visual "data" is lost ?

Can this be expressed as a percentage ? Can this be compared to what is lost by scanning ?

Can the difference (between scanning and enlarging) be expressed or estimated ?

I ask, because I stumbled across some older Silver prints that I made from medium format and 4x5 - and was surprised how natural and analog things look, when no Unsharp Mask and other "corrections" have been applied.

[Ron Marshall]

Ken, this comparison, while not numerical, gives some idea. Compare contact print to enlargement and digital prints:

http://www.custom-digital.com/

MTF charts would be a good measure for what you ask.

[Drew Wiley]

If you've got top quality optics, including precise negative carrier glass, and have
everything aligned and tuned in, and flare under control, you can typically enlarge a large format original with no visible loss whatsoever to the naked eye, say up to
four or six times the original. Of course, higher contrast prints will appear sharper than lower contrast ones, and the nature of the film itself and paper surface are also factors in perceived sharpness. This can certainly never be said for digital prints. No doubt someone will want to interject some motheaten hogwash about "normal" viewing distances - "the bigger the print, the farther away people will view it." Bull. For a billboard the normal viewing distance is about fifty to a hundred yards, if that's what they mean; but much closer and it's sheer mush. I personally like to be nose to
nose with prints no matter what size they are, even if a soft-focus lens was used.

[Oren Grad]

When we enlarge an image with a high-quality enlarging lens, how much visual "data" is lost ?

Well, you said "visual data" rather than just "data", which opens a can of worms.

One question is whether you lose information from a negative as you enlarge and projection-print. The answer is, of course, the process is always lossy, but with impeccable technique you can keep that loss to a minimum.

The next issue is, what can you see? Here the waters get muddier. As you enlarge, up to a point you actually see more spatial information in the picture - more visible detail - but at the price of tonal subtlety. Turn it around: when you contact print, some details in the negative become too small to discern by the naked eye even at grain-sniffing distance. But the rendering of what you can see is exquisite, both tonally and spatially.

Appropriate caveats apply re printing technique, paper surfaces, etc., as mentioned by Drew.

[Oren Grad]

I ask, because I stumbled across some older Silver prints that I made from medium format and 4x5 - and was surprised how natural and analog things look, when no Unsharp Mask and other "corrections" have been applied.

And this is a different point. "Natural" doesn't necessarily require "more information". But it is about the kind of information.

[Brian Ellis]

I doubt that there's much loss at all due solely to the enlarging lens, assuming a high quality lens. It's always been my understanding that the principal loss (of detail and tonal gradations) in traditional prints is due to the fact that paper isn't capable of resolving the same degree of detail and tonal gradations as film. I vaguely recall that Ctein's book contained a chapter about the limitations of photographic paper but I no longer have the book so I can't check.

Tyler Boley's article that Ron cited is interesting but as big an admirer as I am of Tyler's wonderful photography and his technical knowledge, for me comparisons based on degrees of enlargement so massive that all you see are big blobs of some unknown something aren't very useful as a practical matter.

[Nathan Potter]

Ken, I think most people here will answer you based on their visual perception experience. That will not be quantifiable in any sense but just intuitive based on someones experience.

OTOH I believe that one could quantify the difference between an enlarging lens and a scanned image by examining a print produce both ways using a scanning microdensitometer of sufficiently small aperture. That densitometer data could then be compared to densitometer data from the original negative. After some considerable thought and observation of the results one would need to come up with a set of standards in order to tabulate the results in an intelligible fashion. Come to think about it I think that the prints might want to be a positive on film for the purposes of microdensitometer scans.

The scanned print is a bit more complicated owing to effects that can be introduced by the printer. I suppose extraneous artifacts could be largely eliminated by turning off or minimizing arcane software functions but I'm not a digital savvy person; (my body is totally analog).

Nate Potter, Austin TX.

[Oren Grad]

I vaguely recall that Ctein's book contained a chapter about the limitations of photographic paper but I no longer have the book so I can't check.

Ctein's tests established that with proper contact printing technique - and that's not a trivial matter - black and white silver gelatin printing papers are capable of recording information far beyond what the unaided eye can discern.

[Ken Lee]

In general terms, it sounds like there is negligible "noise" introduced by enlarging.

Ignoring grain altogether, it sounds like whatever "data" we lose, can be attributed to magnification of the original, which merely reveals the flaws that are already there: the performance of the lens, limited depth of field, etc.

If we consider the influence of grain, then again, enlargement is merely revealing the "noise" inherent in the graininess of the film/developer combination.

[Drew Wiley]

Some of Ctein's evaluations of the potential of contact prints were based upon looking at things through a microscope, literally. His personal enlarging equipment is
not really sophisticated enough to make a truly objective comparision, even though
he acquired or borrowed a range of top enlarging optics for those studies. His actual
darkroom setup is fairly primitive. But those of us who attempt to optimize enlarging technique do essentially the same thing when we view the projected image
through a high-quality grain magnifier. A ten power magnifer on just a 20X24 print
is equivalent to a nose to nose look at the print sixteen feet wide! No paper is capable of this level of resolution, although color polyester base comes the closest.
So at this level we're really talking about science, not about ordinary visual perception. Most truly modern enlarging lenses at correct magnification ratios will
give excellent results. I'd be a lot more concerned about questions of tonality, and
actual visible nuances. Of course, little things add up; so I personally use the finest
enlarging lenses and carrier glass, etc, that I can afford. But as nitpicky as I am
about all this, the esthetic issues far more important. And for me personally, digital
prints never look truly photographic. They might be nice in other respects, if well
done, but seem to belong to a different category altogether.

[Bruce Watson]

When we enlarge an image with a high-quality enlarging lens, how much visual "data" is lost?

Can this be expressed as a percentage?

There is of course some loss. Has to be, no system is perfect. You get optical losses (light transmission, distortion, aberrations, etc.) from the enlarger/lens. Losses from alignment issues. Losses from paper issues. Etc.

As a side discussion, consider the long running arguments about condenser vs. diffuser vs. cold light vs. whatever.

If there wasn't some loss of information (or at least, some change to the information), same size prints from the same negative, one contact printed and one from an enlarger, would be identical. There have been a number of tests done to show that in fact they are not identical.

Can you express this loss as a percentage? Probably not in any meaningful way. Your best bet for a comparison is probably through modulation transfer functions (MTFs).


Can this be compared to what is lost by scanning?

Not really. The methods are too different. With enlarging you always use all the information contained in the negative. Doesn't matter how much enlargement, you always use all the information available.

With scanning, you decide how much information you are going to collect from the negative up front when you select a scanner resolution. So in printing from a scan you do *not* use all the information contained in the negative. You use as much as is "needed" but no more.

Since scanning doesn't necessarily try to transfer all the information from the film to the print, while enlarging always does, I don't see how you can make a logical comparison of losses between the two methods.


Can the difference (between scanning and enlarging) be expressed or estimated?

For a given enlargement level you can probably compare MTFs. But I don't see how you can make a meaningful generality. IOW, I don't see how you could make a meaningful statement along the lines of "enlarging is x% efficient and scanning is y% efficient."


I ask, because I stumbled across some older Silver prints that I made from medium format and 4x5 - and was surprised how natural and analog things look, when no Unsharp Mask and other "corrections" have been applied.

How "natural and analog things look" is clearly a subjective opinion. One of the reasons there are so many methods (still) available to use in making prints from photographs is that people's preferences vary. All the methods, from inkjet to dye transfer to silver gelatin have their own pros and cons. All make perfectly valid prints IMHO. You should use the process that makes you happy. You are the one doing the work so you get to make the choice. Screw what anyone else thinks -- do what you like.