Conventional printing uses images whose tonality is created by variable-size dots (at fixed positions) called halftone dots. The HP Designjet printer uses a different method for creating tonality, with same-sized dots at randomized positions, called error diffusion.

Error-diffusion patterns are generated by the printer's internal circuitry. The benefit of error-diffusion printing is that the machine appears to generate 'continuous-tone' images while it is creating error-diffusion halftone images. If you look at a Designjet proof through a magnifier, you will see these error-diffusion patterns.

When properly calibrated, and when using an appropriate color management profile for the printer and printing material, an HP Designjet printer can match a print from a printing press or photographic process.

The original image is free of tonal patterns -- it is called a continuous-tone image.

The traditional halftone image (exaggerated here so you can see the dot patterns) shows clear evidence of the dots, their colors (cyan, magenta, yellow and black) at different printing angles.

The error-diffusion technique creates dither patterns that create tonality in an image. These patterns are exaggerated here so they can be seen. Error-diffusion images print well, and look great when generated on an HP Designjet printer.