"Michael Meric" wrote in message
I noticed that the CS IV slide scanner does about 2900 dpi. The CS4000
does
4000 dpi. Can anyone tell me how much dpi is represented in a quality
color
magazine image or in a quality color image in a book?
Is 4000 dpi over kill for almost any "non-billboard" use, or is it a versatile resolution which is good value for money?
How does one calculate the relationship between dpi, lines, pixels, bit depth?
Forget about everything except pixels. For the highest quality prints, you need 300 pixels per inch as measured on the print. So decide on the print size in inches, multiply by 300, and you have the required size of the image in pixels. For a merely very good print, 250 pixels per inch will be quite adequate.
A Nikon Coolscan 4000 produces 4000 pixels per inch as measured on the slide. A 35mm slide is about 1.5×1 inches, so that’s about 6000×4000 pixels. Printed at 300 pixels per inch, thats 20×13.33 inches, more than adequate for an excellent 19×13 inch print assuming that the slide was taken on excellent film using an excellent lens on a solid tripod by an excellent photographer.
For good, rather than excellent, slides, a Nikon Coolscan IV at 2900 pixels per inch provides quite enough resolution. But the big difference between these two scanners is the greater dynamic range of the 4000, which provides better highlight and shadow quality. For excellent film processed by an excellent lab, you will need the 4000 to avoid blocked up shadows and washed out highlights in high contrast scenes. But for low contrast scenes or merely good film processed by an average lab, the IV should be adequate.
A good drum scan will give you 8000 pixels per inch and, more importantly, even better dynamic range, which will be needed to get the absolute best results from professional quality slides.
The batch loader for the Nikon Coolscan 4000 is very finicky about slide mounts. I have never had much luck getting it to run unattended. If you have old cardboard slide mounts, forget it. If you have plastic slide mounts, check the user’s manual to be sure they are compatible with the batch loader (none of mine are).
For scanning a lot of slides, Digital Ice^3 is an absolute necessity for removing dust and scratches. It uses an infrared channel and is so much better than Photoshop for this purpose that you should not even consider Photoshop.
If you need to salvage badly exposed or off-color slides, it is important to make exposure and color corrections using the scanner hardware. For reasonably good slides, Photoshop
will do nicely.