scan dpi vs printer dpi

[Guest_imported]

for best results when printing to a printer with a 600dpi engine, what dpi should i scan images in at?

photoshop help only says, "For best results, use an image resolution that is proportional to, but not the same as, printer resolution."

is there a general rule? i think i heard somewhere that you want to scan images in at 1/3 or 1/2 of the printer resolution. (so i would scan in at 200dpi or 300dpi) does this sound right?

any feedback is appreciated. thanks in advance.

 

[carlow]

There's much you can say about dpi.
One of the things to keep in mind is the size of the document you wan't to scan. If the orginal document and the document that will be printed don't differ much in size you can scan at a reasonable rate.
One thing you must know that scan dpi's are not the same as the dpi's of your printer. What is important are the lines/inch of the printer.
Let's say that the output resolution of your printing device is 100 lpi. Your original document can be scanned at 200 dpi. If the printed document must be enlarged a lot than you go for more dpi.

The dpi of the printer has to do with the exactness of the details in your document, the lpi is the rastering factor by which the printer can work.
A newspaper has 90 lpi raster; a glossy magazine can go up to 150 lpi.

If you scan with a lot of dpi and your printer hasn't got a high lpin the printing process will take a lot of time (the printer first calculates the big file, sends it to the printer and afterwards throws away everything that it can't use for the defined lpi.

Hope this is a help
grillhouse

 

[hohriver]

That is excellently detailed advice given above—but I wanted to add the obvious: where it's 'dpi' for printers ( but more significantly lines per inch or lpi ), it's never dpi for scanners, but 'ppi', pixels per inch.

As a general rule of thumb, I think your output goal is a predetermining factor of your scan resolution: why run a 300 ppi scan on some image which will end up 72 ppi on a website? On the other hand, if you intend to incorporate the image in print form, maintain a much-higher resolution; then in Photoshop, uncheck the Resample box, and amend the resolution to reflect your printer output capacity. For example, with a topend Deskjet printer, say an HP 2000 series, we know that the resolution should be about 130.
This will improve the acuity of the image, even while reducing the overall print size.

I hope this is of some help.