How much DPI does an optical print have?

[Ben Rubinstein]

I usually print on a Kodak LED paper straight onto Ilfords digital Cibachrome paper. The machine cannot print at any other resolution other than 250DPI. I've never been happy with the B&W output of chemical printing onto colour paper and recently tried a particularly hard to print image on a friends Canon 8000 printed. The paper was nothing special but the neutrality and contrast, especially in the blacks, was really mindblowing.

I had originally sized the image at 250DPI prior to PK-ing it and was worried that the inkjet which is capable of so much more would show the resolution to be lacking in a way that LED style continuous tone printing would better allow for. Well, I've been staring at that 16X12" prints with my eye to the surface and damn if I cannot see any lack of resolution or detail period! All the detail down to the finest grain (it was a film scan) is there, all present and correct. I've known for a while that I can't see any difference between 250DPI and higher in prints larger than 8X10" but now I'm wondering whether magnifying glass aside, the human eye can see the difference and if not or to the vast majority of humans not, what the point of printing at a higher resolution (uprezzing to do so) is at all, given that fine art prints are not viewed under microscopes and the difference cannot be seen with your nose touching the print.

If the detail is not there then that is one thing, uprezzing to give an apparent look of more resolution makes sense. However uprezzing higher than what is necessary for the human eye to view seems to me to be non sensical, be it 250DPI or 300DPI, whatever the consensus it about the limit that humans can recognise.

Which also brings me to the question, what would be considered the optical resolution in DPI of a darkroom print? I found my cibachromes to be lacking in the resolution resolved on 645 trannies which a good scan (Imacon 868) easily brought out, in an optical print the fine resolution was neither sharp nor detailed. I know that this print lovingly worked from a high resolution scan with careful contrast and sharpening is about twice as detailed as the optical print was, at the same size and printed at 250DPI...

Any comments?

[Mark D Segal]

Ben, I can't remember where (perhaps Wayne Fulton's "Scantips"  some years ago, but not sure), however I did read in the context of scanning resolution, a view that the maximum resolution of a chemical print is equivalent to about 200 PPI. The context was that any one scanning a print can use any resolution they want, but they won't get a better outcome than the resolution of the original, which was an argument in favour of scanning the film rather than the print). There are estimates of the limits of human resolution measured in LP/mm (I believe Michael has written about this on this website), but I'm not sure whether there is a generally agreed limit in terms of PPI. Personally, I find it difficult to see much difference of detail rendition between 240 PPI and 360 PPI in Epson prints I have made at both resolutions, but if you look hard enough there is *a little*. Beyond 360 I believe it becomes more and more imaginary. Below 200, deterioration is less difficult to observe. There are of course other factors that intervene comparing a Cibachrome print with a digital print - it isn't only a matter of "resolution", but also apparent detail is affected by noise, grain patterns, etc.