** 1 page regular / 868 words **

Calamus Secrets

Calamus SL has enormous power. Aside from many of the built in 
functions Calamus is designed to be "modular"; meaning that aside 
from the basic program many functions come as modules. Once loaded 
a module behaves as an integral part of the program. In other 
words, the new functions contained in the module are accessed in 
the same way as the basic functions. The whole process is 
transparent to the user.

While many modules are standard with the program there are at 
least 40 optional ones which do everything from allowing the 
import of Postscript and Encapsulated Postscript to calibrating 
your monitor. This article will explore one of the more esoteric 
modules, the Star Screening Module.

Star Screening is a brand name for what is technically known as FM 
modulation or Stochastic Screening. FM modulation is a way of 
converting a greyscale or colour image (8 or 24 bit) into dots for 
printing. Well, you might say isn't all printing done via dots? 
Does Barkin not know that with the exception of dye sublimation 
printers, all printing is done via dots? Yes, yes, I know about 
this phenomenon. But conventional screening involves the creation 
of printer points. These printer points consist of "groups" of 
dots laid out in a grid (screen).

Since most home printers have a limited ability to lay down dots, 
they are further limited when they must group these dots into 
printer points. Even the 1440x720 dpi Epson is not normally 
capable of printing out camera ready copy for the purpose of 
getting professional results. Indeed these printers come with 
drivers that "dither" the image for better results of home output. 
Dithering consists of the software simply converting the areas of 
colour into individual dots of CYMK (or black for greyscale 
images) bypassing the conventional grid of a screened image. This 
process is one that I refer to as poor mans stochastic screening. 
Calamus, along with quite a few other programs on all computer 
platforms, have this capability.

True Stochastic Screening goes one step further. The software not 
only dithers the image but it "looks" at each area of colour and 
makes intelligent (user definable) decisions as to how to make the 
CYMK dots. Decisions made for one area are then considered for the 
next area of colour. This results in much higher contrast and 
definition than either conventional screening or standard 
dithering. So on my Epson I get better results at 720 dpi than 
Photoshop which prints at 1440x720 dpi. The Calamus implementation 
of this is of a very high quality.

There are two versions of the Star Screening Module. The Light 
version, limited to 750 dpi and the Pro version, which has no 
limitations. The Pro version can additionally convert the new star 
screened image into a conventional TIFF file and allows exporting 
the resulting files. One other problem with both versions of the 
module is that they are memory intensive. Both versions of the 
module can only process small images unless you have lots of 
memory - in this sense there is no difference between the Light 
and Pro modules. So apart from this limitation of the process, the 
Light version is a usable demo of the Pro version - or is it?

Well, I and others have found that everything the Pro version does 
can also be accomplished using the Light version. Not only that 
but there are ways of overcoming the memory limitations. Thus for 
the price of 50 Euro dollars you can have a program which does 
what on the Mac platform would cost a minimum of 600 dollars, with 
a similar price on the IBM platform. How is this done?

After an image is Star Screened you can simply tell Calamus to 
"group" the frame. You can now use the optional Bridge module to 
either export the image or convert it into a CYMK frame. (a star 
screened image is no longer 24 bit - it is a 32-bit file). You 
could also use the user definable tiling frame and Bridge to 
export the new frame as a 32-bit CYMK image. The Light version of 
Star Screening allows higher then 750 dpi screening - you simply 
can't print the results. But once converted to a TIFF file you can 
do whatever you want with the image.

Shortage of memory can be overcome using the program Outside. This 
superb utility allows you to turn your hard drive into usable 
virtual memory. You must tell Outside to use Calamus AND 
additionally specify the Star Screening module itself. There's a 
lot more to getting good results from the Star Screening module, 
but the above will allow you to make full use of the modules 
potential at unlimited sizes. Until next issue...

** Images and captions **
** CS14_1.GIF **
The Star Screening Light Module and, by adding a screenshot, the 
other user definable settings.

** CS14_2.GIF MUST BE USED AT 1:1 SCALE OR IT WON'T WORK! **
The before and after result of Star Screening a flower. The 
resulting image is a "fixed format," which means it must be 
printed at the exact size it was star screened. Due to the nature 
of Atari Computing's printing process I doubt these images will 
print correctly...