Software Dithering and Error Diffusion
Printers include software features that further trick the eye into seeing pure continu-
ous tones.
Inkjet printers employ ditheringtechniques, which print random colored dots to
smooth harsh lines and blend colors that cannot be printed accurately using the
fixed set of inks. Wherever lines on the image create harsh differences, such as
between the corner of a building and the sky, the printer will print lighter (or darker)
shades in a somewhat random pattern to fool the eye into seeing smooth edges or
smooth continuous tones.
You can see the dithering created by the printer to help simulate a continuous tone
along the edge of the structure (see Figure 18.3).272 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY
FIGURE 18.3
Another soft-
ware trick is
dithering, as
shown in the
scan of an
inkjet print.Error diffusion is another software technique used by inkjet printers. Dots of the
opposite color near a specific pixel are printed to create the illusion of the correct
color. For example, if a green pixel is printed and the dots cannot match that green
color, the printer software will print much greener dots near the pixel location that
overcompensate for the error. This process continues across the image. The eye is
fooled into seeing the same color as on the original digital image or negative/print.