HP QMS 1660 setscreen, setscreen

Gamma

Correction,

Halftones, and

Screens

The following illustration shows the relationship between screen fre- quency, gray levels, and print resolution. As the screen frequency increases, the number of gray levels decreases.

300x300 dpi

Gray Levels 600x600 dpi 250

201

200

150129

100		73
51
50	33	19	33
			9
0
42	53	71	106
	Screen Frequency (lpi)

The number of gray levels that your printer can produce depends on the screen frequency and the print resolution. The default value for screen frequency using 600 dpi is 71 lpi. This typically allows 73 different levels of gray. The default value for screen frequency using 300 dpi is 53 lpi. This typically allows 33 different levels of gray. You can change screen frequency through your application or by using the PostScript setscreen operator.

The extra gray levels available through higher resolution provide a smoother shift from the darkest black to very light grays while higher resolution provides sharper image outlines.

Screen Angle

A screen angle is the angle at which a halftone screen prints. The default screen angle for your QMS 1660 Print System is 45° at 300x300 and 600x600 dpi. This is the normal angle for black and white printers. At 1200x600 dpi the screen angle is 26.56°.

You can change the screen angle through the PostScript setscreen operator.

5-6 QMS 1660 Print System Reference