Category 16,  Topic 20
Message 45        Wed Apr 29, 1992
ISD [Nathan]                 at 16:31 EDT
 
Mario recently answered a customers question in hard copy, regular mail. Yes,
some poeple still do not own a modem. :-) Anyway, one of his answers caught my
eye. I thought you might like to see his response to a question relating to
the Raster Generator, as follows;

The Raster Generator functions in the capacity of producing screens in the
manner that printers can actually use. Each resolution has its own optimum
level of Line screen adjustments i.e.; a 150 raster/line screen at 0 on a 300
dpi laser printer will only yield 5 intensity levels; at 1200 dpi it will
yield 65 intensity levels, at 2400 it will yield 257 intensity levels. To
define the correct screen settings for you printer you have to decide on the
number of grey levels you are willing to live with 4, 9, 16, 25, 36, etcetera.
If you decide on 36 levels then you have to take the square root of 36 = 6,
then divide it into your resolution which would be 300 dpi 300/6= 50, which
allows you a 50 lpi raster/line screen. Divide this by 2.54 to give you your
settings in lpcm, 50/2.54 = 19.7. This would produce a fairly coarse raster.
Use the same method with other grey levels i.e.; 16 levels = 300/4 = 75 lpi =
29.52 lpcm and 9 levels = 300/3 = 100 lpi = 39.37 lpcm.

The Raster Generator also allows the definition of these line/raster screens
for each colour layer. The problem lies in the fact that process colours use
angles other than multiples of 90. Process colours require specific angles:
Black 45, Cyan 15/105, Yellow 0/90 and Magenta 75. These angles can produce
variances in these angles from true. I suggest that if you are working in spot
colour, or one colour mode, you set your angles to either 0 or 45. 0 will
produce rasters like those from Calamus 1.09N.
