Photo Paper Resolution?
Roughly what is the best case (i.e. glossy paper and good enlarger optics or contact print) resolving power of photo paper?
Generally, it is uncommon to measure the resolution and the granularity of papers. They are often degraded due to backreflection and internal reflections due to the lack of antihalation.
However, OTOH, it is almost impossible to see this in a print at normal viewing distance.
I have posted some resolution charts scans on the emulsion making and coating forum where I coated the same emulsion on several different papers both baryta and non-baryta. It became apparent that the rough non-baryta papers suffered a visible degradation of resolution due to the paper fibers themselves.
So, resolution of baryta and titanox papers are quite good in spite of losses due to the physical nature of paper itself due to the higly smooth surface, and the rougher the surface the less resolution.
I suggest that you get a resolution chart from EK, some other mfgr, or from Edmund Scientific. Any one of these makes a very good chart that you can use to make your own measurments.
a colleague of yours, Detlef Ludwig, the man behind the Gigabitfilms, takes a somewhat different view:
He refers to a phenomenon in human vision which I try to translate as `nonius-acutance´. Which would enable man to have a 10-times greater acutance than that measured in mono-ocular tests. (Something beyond my scope.)
Thus he demands a resolution of 100 lp/mm of the photo-paper. He proposes to make use of graphic-films emulsions.
Further he proposes an antihalation dying of the paper-emulsion, which would be discoloured in the alkaline developer, a techniques which successfully had been used in optical typesetting.
(in German: http://www.gigabitfilm.de/download/n...hotopapier.pdf)
Well, I gave a bad - or incomplete answer last night.
Paper prints are the result image reproduction through an entire system. That system is comprised of the film, camera, enlarger and paper not to mention the processing chemistry involved.
Now, unless you are using ULF images and contact printing, the enlarger and lens stage has a lot to do with the final image.
In tests, it can be shown that apparent imaging sharpness decreases on the approximate order RC glossy > FB glossy > RC matte > FB matte > Smooth plain paper > textured plain paper. I have run these tests and as I said, I have posted some contact print results here. At normal viewing distances, the results are hard to discern. These were LF originals contact printed emulsion to emulsion.
It is only when one gets to color paper that the loss in sharpness in a paper can be seen by the naked eye. So, for this reason and to adjust for paper speeds, color paper contains acutance dyes to improve sharpness. They need no antihalation layer, as the yellow layer is on the bottom and the eye has the least sensitivity to yellow dye in terms of sharpness.
So, I will have to respectfully disagree with Mr. Ludwig. I'm sure that the films are capable of high resolution as claimed, but the final print will still depend on the TOTAL system used. To fix this up, one would have to use an ULF format, in which case a gigabit film would hardly be necessary in the first place.
On a further note, in getting resolution there are two phenomena to be observed in a final print. They are bloom and fill in. Bloom is an instance where a black line seems to expand and be wider than it is. Fill in is where a white line in a black background seems to be smaller than it is. For this reason, resolution must be tested with both positive and negative resolution charts. Without this type of measure, you can get misleading results.
In the final analysis, if this were a problem, it would have been observed and commented on industry wide years ago and customers would have forced a correction on the manufacturers. This has not ever taken place. Therefore, I have to say there is empirical evidence to support what I have said.
Thanks for the comprehensive reply, PE.
But why are colour papers more critical in showing a lack of acutance?
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The surfaces formed by the 6 layers in color paper act as tiny mirrors, and the couplers and silver also present reflective surfaces within each layer.
Originally Posted by AgX
For this reason, there is back scatter from each layer, and internal scatter from the particles in the paper. (This is also true of color films)
The acutance dyes are added to both film and paper (color) to reduce these multiple internal reflections.
There was a misunderstanding. I somehow thought you meant that at an optical (measured) resolution comparable to b&w papers the visual inspection of colour papers would show a lack of sharpness earlier than b&w papers.
There is a detailed article by Ctein in the March/April 2002 (Vol. 23, #2) issue of Photo Techniques that will answer your question in detail. The short answer is that any paper with a resolving power of 30lp/mm is "perfectly sharp". In the article, "perfectly sharp" is "...when you can see no visual improvement by making it sharper.".
There is an article in the table that has the following data:
Agfa MCP RC (no filter) 80-100 lp/mm
Ilford Galler #2 80 lp/mm
Ilford Multigrade IV RC (no filter) 65+ lp/mm
The issue is still available at www.phototechmag.com for $5.
I'll go out on a limb and say a bare minimum estimate might be 500-1000 dpi. I feel that when I scan a print, to really do it justice I must scan at ~1200, but then there is the whole issue of sharpening which introduces a major fudge factor, not to mention the enlarger lens issues and all that. I guess one could scan a res chart printed on RC in a methodical way and get a better answer.
Originally Posted by 3Dfan
Looking at 300 dpi lightjet images with a loupe, it is apparent to me that the paper has, what, ~2x more resolution than is actually being used?
Moreover, 500 dpi digital contacts look fine to me but 300s do not, so I think that's another indicator that nothing-special RC paper must be able to deliver at least well upwards of 500 dpi.
I frankly don't know what the uppermost limit would be, I learned some new things from the comments above. But in practice, as was mentioned, there are so many other ways to lose print detail, apart from hitting the actual limit of paper resolution. Even with contact prints, I really doubt that I am operating at the limit of the paper, with my own practices. I did some pinholing on paper and was pretty astounded at what was resolved.
Last edited by keithwms; 09-28-2007 at 02:05 PM. Click to view previous post history.
No science here - just observation. Most printing papers have pretty crappy resolution. They are not designed to show much under a loupe. I find that it is better to scrutinize a negative with a loupe than to make an enlargement and look for sharpness and detail there with magnification. Prints, even 8x10 contact prints do not record all the detail in a negative,
My photos are always without all that distracting color ...