Digital Photo Printing

• Above this print density, pixels begin to blur together so information will be lost.
• At about 2 DPP (print dots per pixel), individual pixels can be visually unique colors; though pixel color depth will be poor.
• Example: With a Canon 40D and a 1200 DPI printer, 1200 DPI / 2 DPP = 600 PPI. So, for 2592x3888 pixel images, the lower limit is a 4x6 inch print
• Note: that a Canon Pixma Pro 9000 claims a 1200x2400 DPI print resolution but testing with the CT-PrinterTest target suggests a 400 DPI maximum to retain any visible definition of features.

• Below this print density, color print density is wasted. This value is dependent on viewing distance.
• Example: With 16 DPP to provide full 8-bit color depth with a 1200 DPI printer -- 1200 DPI / 16 DPP = 75 PPI. So, for 2592x3888 images, the upper limit is a 34x51 inch print. However, the viewing distance would have to be about 60 inches to keep the pixels "just visible" and would require a 36 inch printer. A compromise at a 6-bit color depth per pixel would allow a 150 PPI print and so a 17x26 inch print. This is still large. A more common print paper is 13x19 inch which requires 200 PPI. 200 PPI is convenient because of reduced conversion errors as 1200 DPI divides nicely by 200 PPI.
• Note: 400 DPI is the printer dot resolution, not the image PPI which represents the number of pixels printed per inch. DPI/PPI = DPP (the number of dots printed per pixel). If DPP = 1, then color resolution would be terrible; just a single dot to describe a 24-bit JPEG pixel.