Scanning Resolutions

When scanning using the Coolscan (i.e., scanning 35 mm slides and negatives), I use the maximum resolution of 4000 dpi (dots per inch). This yields scans of 23.5 megapixels for film and slightly smaller for slides. All should be trimmed down before printing or posting, as the scanned area is slightly larger than the picture size.

The usable resolution from slides and negatives varies, depending on the quality and condition of the source material. I often scale a copy of the image (I leave the original intact) to 50% of the height and width, yielding an image one-fourth the size of the original. Batch processing -- having Photoshop perform the same function on a group of files -- works well for this. For most uses, this high-quality five megapixel image is plenty.

When scanning using the flatbed, I typically use a resolution of 600 dpi. The size varies, depending on the source material. These need to be trimmed down, too, as I scan an area slightly larger than the source to ensure I don't miss anything.

In the past, I scanned many images at 300 dpi, but have moved away from this. Storage is cheap, and the leap from 300 dpi to 600 dpi makes a difference on some pictures. I have not found any printed material that requires more than 600 dpi, although I guess it may be possible for some source material.