Image to Print

pixels per inch (ppi) describes the number of pixels in an inch of an image at a given size

and dots per inch describes the number of ink jet dots actually printed

If I have that correct, then would some one explain the translation from ppi to dpi when:

ppi>dpi and ppi<dpi

Is there a relationship formula, some type of averaging, or what??

Thanks in advance.

ppi and dpi do not really correlate; and the resolution in dpi provided by different manufacturers are not really comparable either. Every manufacturer uses a different way of describing their maximum resolution. dpi is the number of dots a printer can fit into one inch, but they may not be discrete separate dots taking up separate real estate on the paper like ppi. There may be varying degrees of overlap of ink droplets created by the inkjet nozzles as they pass back and forth, sometimes multiple times over any area, sort of layering the ink to varying degrees.

Generally for high resolution prints manufactureres differ in what they recommend as to the ppi you should choose. Remember as well that you should consider ppi at the print size you are choosing - so that your file size may change depending on the final print size you want. Epson recommends choosing 300-360 ppi for high resolution prints, Canon 200-300ppi, and HP 150-300. (The smaller numbers are minimum recommended for high quality prints)

Finally consider viewing distance of the print. A rule of thumb is that the viewing distance for a print is 1.5 X the diagonal of the print. So larger prints need fewer dpi to look as sharp from the appropriate viewing distance. Fewer dpi on a large print may actually give the appearance of enhanced sharpness.

Hope this is all clear as mud. <_<

Loftus got it right.

As a rule of thumb for large display prints (just did one to 24x36"), I usually set my files to 200dpi at the final size, which seems to give plenty of resolution.

Jack