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Enlarged digital negatives
Today I tried to put a digital negative into the enlarger instead of printing with it by contact. While I had a lot of success producing fine prints with a lot of processes, including silver ones, all by contact, the enlargement of digital negatives seems really to suck. I guess the informations contained in such negative are too poor and not suitable for enlargement. The graytones were almost ok, but the image sharpness was really bad and also I got a lot of noise.
Has anybody else tried this before?
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How large was the negative? What percentage was the enlargement?
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No. I have not tried it and wouldn't even consider it. The original book on this topic was Dan Burkholder's Digital Negatives for Contact Printing. That pretty much told me what digital negatives were supposed to be used for.
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 Originally Posted by Michael Koch-Schulte
How large was the negative? What percentage was the enlargement?
mmm I made just a quick test, the negative was calibrated for contact on multigraded paper... so I just used the same negative for enlargement and was about 12x12 cm sized. I enlarged it to 24x24 or something and the quality was shitty already...
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Originally Posted by Fulvio
mmm I made just a quick test, the negative was calibrated for contact on multigraded paper... so I just used the same negative for enlargement and was about 12x12 cm sized. I enlarged it to 24x24 or something and the quality was shitty already...
You are correct in that there is insufficient information in a digital negative (at least one made with an inkjet printer) for enlargment. Bear in mind that the maximum resolution in a digital negative is something on the order of 8-10 lppm. If you enlarge such a negative even one time you drop below the threshold of reslution of the human eye.
Sandy
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Sandy,
I don't understand. How does one go about computing line pair per mm (lppm) in this case? Assuming I'm starting at the current max of 5760 DPI, I divide by 25.4 to get the pixels per mm, 226.7, even dividing this by 4 yields lots of resolution. Where'd I go wrong/right? Or is the limitation the grounds on which the ink is jetted? ~m
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Originally Posted by Michael Koch-Schulte
Sandy,
I don't understand. How does one go about computing line pair per mm (lppm) in this case? Assuming I'm starting at the current max of 5760 DPI, I divide by 25.4 to get the pixels per mm, 226.7, even dividing this by 4 yields lots of resolution. Where'd I go wrong/right? Or is the limitation the grounds on which the ink is jetted? ~m
Michael,
You begin with the premise that regardless of printer resolution in dpi there is very little to be gained in terms of resolution by setting the file spi at more than 360. If you set file resolution at 360 spi (at the print size), a resolution test of Pictorico OHP with an Epson 2200 or 2400 show that it has a maximum resolution of about 7-8 lppm. This is calculated as follows: 360 spi file size divided by 24.5 divided by 2 equals 7.4 lppm. It has been shown that it takes at least 2 ppi to equal resolution of one lppm, and that is optimistic. Setting the file size to 720 at the print size may result in a very small increase in resolution, but not much since the OHP materials also limits resolution to around 8 lppm. In fact, many people will not see a difference between file size of 240 spi and 360 spi at the printing size, and 240 spi is about same as 5 lppm.
Output to an Imagesetter or laser printer (Lambda for example) can result in slightly higher resolution. For examle, a negative from a Lambda on Ilford FP4+ is capable of around 16 lppm, assusming the Lambda is operating at 400 dpi.
As you can see, you don't want to confuse output resolution with printer resolution. There are many good sites on the web that deal with this, see for example http://www.mkprod.com/ResolvingResolution.htm
Sandy
Last edited by sanking; 05-13-2006 at 04:22 PM.
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