[Maflynn]

I picked up an epson scanner that's capable of scanning 24 or 48bit.
I'm at a loss to see any difference when I scan a photo (not a negative) at 24 or 48bit and the dpi is set up beyond 300. The file size is humongious however when I select high (over 900dpi) DPI.

Is there a resource, that I can pursuse to get the finer touches of scanning and how the various settings interact with each other.

Mike

[Dark Helmet]

Use 72 DPI for scanning for web.

150 DPI for letterheads, simple graphs

300 DPI for print

24 bit colour is all your really need, the rest is just marketing.

[OreoCookie]

Scanning at a resolution higher than than 300 dpi is pointless, unless you scan negatives. All photos are printed at 200 or 300 dpi these days.

[almaink]

Originally Posted by OreoCookie

Scanning at a resolution higher than than 300 dpi is pointless, unless you scan negatives. All photos are printed at 200 or 300 dpi these days.

Ah just where did you get that info from? Even desktop inkjets print at higher res than that now.
I output at 2032 for 133line film and 2450 for 150 line. If I'm scanning text I'll do it 600 DPI sometimes 1200 depending on the image. 48 bit will give you deeper shadow detail however you also need the equipment to output it so for most it is overkill.

[andi*pandi]

general rule of thumb is twice the linescreen it will be printed at -- meaning press. 300 is a good default. 350 if you know you'll be going on excellent paper that can take a small dot and the 175 lines screen.

I sometimes scan line art at higher res (600-1200) to work with it before eventually getting it back down to 300.

[Dark Helmet]

Personally even if it is for web I still scan it at 150 DPI and down-sample it in Photoshop. The results are much cleaner.

[tooki]

Originally Posted by almaink

Ah just where did you get that info from? Even desktop inkjets print at higher res than that now.

Not the same thing. Printers have to use halftoning to achieve multiple colors. It takes several dots to make a single pixel. The pixel count (which is all you need to scan) need not be higher than 300dpi.

tooki

[gbhgbh]

Here's a great site to learn about scanning:
http://www.scantips.com/

[art_director]

Many semi-accurate replies to this question. Before scanning one must first determine the output size and consider the media. For example, if you scan a 35mm slide at 300dpi 1:1 scale, it will look like crap as OOH.

Of course, when you're doing that sort of work you're probably having a color house spin it on a drum scanner.



( insert lame moticon here )

[Maflynn]

Thanks for all of the info, keep it coming.

[yugyug]

For print, I think generally you want to scan at the resolution the source was printed, i.e twice the linescreen for offset prints as stated above.

How do you find out the linescreen? I have a printer's glass - a maginfying glass fixed above a ruled square that sits on the paper - you use the ruled measurements to count off the dots. I am SURE there must be a better way but I don't know what it is.

Scanning at lower a resolution lower than which the source was printed can produce good results, even advantages if the end product is at a lower relative resolution i.e for a large scan that will printed smaller, or for the web as mentioned above. But obviously you lose design flexibility and run the risk of printing a blurry image.

Scanning at higher resolution than which the source was printed can produce unwanted effects; the scanning will pick up rosettes, printing dots and have a moire effect, which can be a pain in the butt to remove. I guess their are exceptions, scanning text at higher resolutions that that it was printed would generally be ok because text is usually a solid and doesn't have rosettes. I guess if the text is very small and needs to be OCR'd it would help.

Oh, if you are scanning proper photos that have been developed, I think you can shove the resolution way up, like as with slides, because the photo is optically produced and the linescreen thing doesn't apply. Maybe the correct resolution to scan at would be something related to the ASA nunber or the amount of silver in the paper .... you can tell I don't know much about this so perhaps someone else can discuss it...?