Photo Paper Resolution?

[3Dfan]

Roughly what is the best case (i.e. glossy paper and good enlarger optics or contact print) resolving power of photo paper?

 

[Photo Engineer]

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.

PE

 

[AgX]

PE,

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/neues_photopapier.pdf)

 

[Photo Engineer]

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.

PE

 

[AgX]

Thanks for the comprehensive reply, PE.

But why are colour papers more critical in showing a lack of acutance?

 

[Photo Engineer]

Thanks for the comprehensive reply, PE.

But why are colour papers more critical in showing a lack of acutance?

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.

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.

PE

 

[AgX]

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.

 

[Neal]

Dear 3Dfan,

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.

Neal Wydra

 

[keithwms]

Roughly what is the best case (i.e. glossy paper and good enlarger optics or contact print) resolving power of photo paper?

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.

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.

 

[fhovie]

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,

 

[keithwms]

Maybe my quick math is wrong but I just did a conversion of lp/mm to dpi, and for the 80 lp/mm number given by Neal, that works out to 4000 dpi:

80 lp/mm x 10mm/cm x 2.54cm/inch x 2 dots/lp = ~4000

...which is a number that I can't even fathom, it's so far beyond the "standard" 300 dpi resolution at which many people print digitally. If that's true then I think that is way, way beyond what one would actually get in routine enlargement. I guess to get those kinds of numbers you have to skip enlargement altogether and shoot directly to the paper over a very limited wavelength range etc.

 

[Photo Engineer]

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,

One of the problems with a print material is the fact that it has a tone scale limited by the reflection cutoff limit of paper. This is generally between 1.8 and 2.2 density units.

That is why a print has far less observable tone scale than a similar slide made from the same negative. The slide can go to densities above 3.0 with the correct conditions.

In many cases, the paper has the data recorded, but it can only be seen by very high intensity illumination at 90 degrees to the plane of the surface.

This leads to the impression that the detail is not there, but is not really related to the resolution of the paper product.

PE

 

[3Dfan]

Maybe my quick math is wrong but I just did a conversion of lp/mm to dpi, and for the 80 lp/mm number given by Neal, that works out to 4000 dpi:

80 lp/mm x 10mm/cm x 2.54cm/inch x 2 dots/lp = ~4000

...which is a number that I can't even fathom, it's so far beyond the "standard" 300 dpi resolution at which many people print digitally. If that's true then I think that is way, way beyond what one would actually get in routine enlargement. I guess to get those kinds of numbers you have to skip enlargement altogether and shoot directly to the paper over a very limited wavelength range etc.

Even a quarter or a sixth of that 4000dpi would still run circles around the current crop of digital minilabs. The reason I asked about paper resolution is that I had recently heard that paper is only capable of 400dpi, which sounded a bit hokey. I thought if that's all it can do, then I should just scrap plans to get a 5x7 for contact prints and stick with 35mm/120. So thanks everyone for your answers.

 

[Gigabitfilm]

Hello, my name is Detlef Ludwig. Never I would start so long ago my pdf-paper, if I would not hold a proof in my hand. Thanks working in history of photography I had a collection of ultrahighresolution-pictures. One of them is a stereocard from around 1860, 9x18cm, edges had been damaged, picture quality perfect, yellow carton, backtitle: „Raglan Castle: Gateway Towers to the South No 301, ...kander Wilson, photographer, Leamingto....“ Comparing to other pictures of photopaper-books/examples, the resolution of this not baryt-coated ? Paper I presume to around 200 line pairs /mm + - 30%. In spring 2007 in Kassel on a forum I show this photography to several german experts, the most interesting meaning comes from Mr. Andreas Weidner, after 30 seconds he said, difficult to translate in that meaning, that this quality enhanced his trust in analog photography.

Of course had there been other people, who saw no difference, perhaps opthalmologic reasons. It is my opinion, that we need a „juridical“ paper in future, that cannot be faked or – a fake is more complicated than ever. I am collecting these experts-meanings for the next step to transfer the technical arguments into psychological arguments for artists.

 

[Nicholas Lindan]

4000 dpi ...which is a number that I can't even fathom, it's so far beyond the "standard" 300 dpi resolution at which many people print digitally.

There is a confusion between ppi - pixels/inch and dpi - dots/inch.

dpi is a measure of tone reproduction more than one of resoltuion.

To simplifiy things greatly: imagine a black&white 300 pixel/inch printer putting down black dots at 3000 dots/inch. Each pixel is made up of 100 black dots. Only 100 shades of grey are possible in each pixel because the black dot is either there or it isn't. This is part of the reason IJ has so much problem trying to do 'simple' black and white.

The quality of the photographic output of an older 300 dots/inch laser printer shows what happens when dpi=ppi.

Lithography where dpi=ppi=~100-300 uses dot size to determine the shade of grey. Lithographic dots also change shape to follow the detail of the image.

 

[gainer]

You could try contact printing a 35 mm frame on printing paper of various types to see if the printed image, under a loupe, has lost anything. Let us assume you have an 8x10 negative you want to print. The viewing distance for that print at which proper perspective is seen is the same as the focal length of the lens that made the photo, usually about 12 inches. IIRC, the angular resolution of the standard human eye is about 1 arc minute, or about 0.0017 radians, which subtends about 12*0.0017 inches at 12 inches. We want the resolution of the printing material to be at least twice the eye's circle of confusion, so it should resolve about 0.01 inches. That is only 1/100 inch. That is only about 1/4 mm. Now, if you are going to make miniatures and expect them to be seen through a magnifier, you will have to amplify the resolution of the printing material by the minification of the print. What qualifies as a miniature worthy of this resolution? If we make it a 2 x 2.5 inch print and examine it through a 4 x loupe, we would want the printing material to resolve about 1/16 mm. You should have no trouble testing the paper once you obtain the proper test transparency. Look in Edmund's Scientific catalog for such things. I would be very suprised if you found a smooth or glossy surfaced paper that would not meet that spec.

 

[dancqu]

News Paper and Magazine Reproduction

In the 50s the usual half-tones for news print ran 80 dots/inch.
I've 60s issues of International Photo Technik which were printed
at 180 dots/inch; very high quality at the time and I expect even
today. Sharp very detailed reproductions.

As for print paper; if your prints don't show sharp don't blame
the paper. Dan

 

[gainer]

Eye resolution.

Maybe my quick math is wrong but I just did a conversion of lp/mm to dpi, and for the 80 lp/mm number given by Neal, that works out to 4000 dpi:

80 lp/mm x 10mm/cm x 2.54cm/inch x 2 dots/lp = ~4000

...which is a number that I can't even fathom, it's so far beyond the "standard" 300 dpi resolution at which many people print digitally. If that's true then I think that is way, way beyond what one would actually get in routine enlargement. I guess to get those kinds of numbers you have to skip enlargement altogether and shoot directly to the paper over a very limited wavelength range etc.

If you were to look at MTF curves for camera lenses, you would see that a very good 50 mm lens may have a central resolution of less than 80 line pairs per millimeter. You should really think of angular resolution rather than spatial. 1/80 mm is 0.000250 radians with a 50 mm lens. You would expect about the same angular resolution with any lens of comparable design and care in manufacture. Thus, the 210 mm lens of a typical 5x7 camera could be expected to have a spatial resolution of about 19 lppm.

The standard human eye resolves about 1 minute of arc, which is 0.000291 radians. It takes a pretty good lens to put into a photograph more than the standard unaided eye can get out of it. True, every optical stage a photo goes through between film and paper detracts from its resolution, but it would be a pretty poor smooth matte or glossy paper that would not present to the average eye all that any lens you or I could afford has to show.

 

[gainer]

I forgot to mention that there will be a difference, as a rule, between a contact print from a 5x7 negative and a 5x7 enlargement of a 35 mm frame. There are inevitable losses in the enlarging process. This assumes that the lenses are of finest quality in both cases.