Best Scanning Resolution?

[themattman]

I recently bought a Canon CanoScan 4400F to archive a lot of pictures. Most are the standard prints you get from the store (don't know the exact dimensions, but it is something like 3.5 x 5.5 inches). I do have a few 8x10 pictures as well.

I plan to use the GIMP to scan everything in and touch up if needed. I noticed that I can scan up to 1200dpi. I know hard drive space is cheap, but what resolution would give me the best quality for the space needed? I tried out a slightly larger picture than what I plan to do and 1200dpi gave me a 120mb file. 600dpi was 36mb and 300dpi was 9mb (using .tiff). The picture quality can't be distinguished unless you zoom way far in.

Should I stick to 300 or 400dpi? Is there a good reason to even go higher if I never plan to make huge prints of the scanned photos?

Also, what would be the best file format to use? I would prefer a lossless format like .tiff or .bmp (lossless?)

Thanks.

[CB5000]

300dpi is fine and it's a standard resolution that seems to be used often for almost anything. If you want to preserve the detail then stick with tiff or bmp. If you want to save some disk space then use jpeg with the lowest compression. I use 200dpi for most of my images in presentations and I don't see a difference with raising the resolution. But the main thing is what you are going to do with the images after you scan it. Do you want to make a poster print? then go with 600 dpi or higher. webpage images, 150dpi or less... photo editing 300 dpi... etc etc...

[crazybus]

Beyond a certain dpi you're not going to be able to resolve any more actual resolution out of a print anyway. I'm not sure how high you can go scanning prints before it becomes pointless but I imagine it's below 1200dpi. As far as archiving the images is concerned, the scanner probably scans at 48-bit colour, so dithering the image down to 24bpp and saving in a lossless compressed format such as TIFF w/LZW or PNG is probably your best bet.

[UberGerbil]

JPEG2000 also offers lossless compression, and may give slightly smaller results than PNG on photographs (PNG will definitely be be better for photos with large blocks of constant color or non-photographic images). But it's not (yet) as widely supported.

Actual photo (chemical) prints from 35mm film rarely show added detail above 300dpi (exception: true B&W film can show more, as can prints made from larger than 35mm film). Depending on the quality of the camera/lens/film (not to mention the photographer -- how sharp is the shot?), even 300dpi can be overkill. Scanning slides is another story -- the actual negatives or positive transparencies show detail up to 3000dpi, but of course they're much smaller than a print. And if you're scanning from a digital print, it's going to depend on the qualities of the printer that made it.

[Aphasia]

As UberGerbil said. Normalt prints rarely show any detail above 300 dpi, that means, to actually get that detail into a scan you need to use 600dpi in the scanner settings, else you will waste detail. That said, true digital prints on photopaper can contain up to 400dpi on paper. Scanning negs is a different story. Color film rarely has that much detail, slide film more, and some odd special black and whites can have incredible resolution, but people usually dont use technicalpan for normal photography.

What it comes down to is to always use double the dpi in the scanner setting against what you know/think the original contains and in some cases, what you need to output. This due to the fact how sampling work. But if i didnt know, i would err on the highside if it was important. And unless you have some special reason, do your processing, then save as something more efficiant than Tiff, even though you can use both zip or lzh compressed tif's. A lossy format still contains more than enough detail at high res and high quality settings as long as you doesnt have too much processing left to do.