Digital Photo Printing

What about color ?

How many print dots are needed for color?
  • The Canon Pro9000 uses 8 ink colors to interpolate 24-bits of RGB color resolution per image pixel.
  • Visual color differentiation is only about 64 of 256; or 6-bit -- 8x8 DPP minimum.
  • So, a 400 DPI print requires about 400/8 = 50 PPI to achieve the this color resolution; higher PPI would cause color quantization increasing the print color error.
  • This also means only a 650x950 pixel image is required to print 13x19 with 50 PPI; or less than a 1 MPix image!
  • However, at 50 PPI, the pixels would be easy to see at 23 inches viewing distance. We'd need 8x that or over 15 ft viewing distance to eliminate the pixelization effects.
Consider a 3888x2592 image printed 13x19:
  • Starting with 3888 pixels, printed over 19 inches means 205 PPI.
  • The Canon Pixma 9000 can print clearly at 400 DPI but this means only 2x2 DPP giving a 2-bit qcolor quantization.
  • Yes, color is visible. No, pixel color is inaccurate.
Clearly, some limits are needed as well as some compromises.