scanning offset print images. recommendations?

[Gregory C]

I have quite a few magazine and newspaper articles (with photos) to scan. I have experimented with SilverFast, using various scan resolutions and various descreening settings.

I have a few queries... of course!


It occurred to me that the virtual resolution of a printed image is the line resolution. For example, 133 lines per inch is equivalent to 133 dots per inch. To me, there is therefore no sense in trying to scan at a higher resolution. It would be equivalent to converting a 96kbs MP3 song to 224kbs. Photoshop and other graphic applications provide various solutions to 'increase resolution' but it shouldn't be done at the scanning stage. (Correct me if I'm wrong.)

Questions:

1. if the line screen is 133, would the best hardware resolution to scan at be 133dpi?

2. if the line screen is 133, should I also set descreening to 133 for the best results?


Accidentally, I discovered that the color of the scan can be fine tuned quite well by prescanning at a higher resolution, and then using Selective Color Correction to 'correct' each of the offset screen colors.

Would there be any downsides to this method?

Since most offset printing is CMYK, is there any way to switch SSC into CMYK mode rather than 6-color mode?


Any other hints in general?

Does anyone have a tip on how to discover/calculate the screen density of the image using SilverFast?

regards
Gregory

[Gregory C]

could somebody from LSI please answer my question?

[Paul Escudier]

I always scan the image to my preffered size at double my normal resolution (i.e. for 300 dpi scan at 600dpi) with no correction and sharpening turned off. Then open in photoshop, if image is part text, part picture use the marquee tool to select the picture(s) only, then viewing the image at 1:1 use gaussian blur until the dots merge together, obviously the image will look very soft. Then resample image down to your normal scanning resolution (i.e.300dpi) which should give a much more manageable file size. You should see a big improvement already, then set levels and add a small amount of USM if image will take it.

[Gregory C]

you make it sound like a simple pancake recipe ;-)

thank you. I'll try that.


any suggestions for working purely within SF?

[Paul Escudier]

Afraid not, while I dearly love Silverfast I think the descreen function is about the only thing that lets it down. The method I use is tried and trusted, I do a lot of scanning of newspaper clippings for a historical archive and lots of these scans of sometimes quite small originals have been used full page in books and magazines. It does take a little practice on how far to go with the gaussian blur though.