                             C_PRNTRS.TXT

Here are a few words about color printing.

For the most part, any affordable color printer can really only print in
seven different colors. When printer manufacturers claim that their printers
can reproduce any of 16.8 million colors this is actually an illusion.
Each individual ink dot of a printed picture can only be either
magenta, cyan, or yellow. Red is the result of yellow printed over magenta.
Green is cyan and yellow. Blue (which actually looks rather purple) is the
combination of cyan dots on top of magenta dots. Black is the mixture of all
three primary colors or in some cases, pure black ink. White is the absence
of ink. All the other 16.8 million colors are approximated by placing dots of
these seven different colors (plus white space) in close proximity. Your
eyes and brain do the blending and you think you see many different hues
and shades.

What this means is that when you intend to print a color image that has
lots of colors and shades, you should enlarge the image so that each pixel
of the BMP file is printed as a block of multiple pixels on the printed page.
It might look a little big and chunky, but the color depth will be
significantly improved as you enlarge the image - up to a point.
Once you enlarge an image 16 times its actual size the effect becomes
redundant and no improvement in color can be seen. This is because any color
that can be stored as a pixel in a bitmap is going to be a composite of red,
green, and blue values. Each of these values is stored as 1 byte, a number
between 0 and 255 - 256 different possibilities for each of the three color
plains. 256 to the third power = 16,777,216. Your printer looks at these
values as follows; Red becomes the absence of cyan. Green becomes the absence
of magenta. Blue becomes the absence of yellow. These "absence of" colors
still have a possible range of 256 different values and the square root of
256 is 16. A block of 16 pixels square, can represent any true color by
careful placement of the corresponding number of primary colored dots.

Your monitor and your color printer work by exactly opposite principles to
display color pictures. When your monitor has no picture on it, it is black.
As you increase the intensity of the red, green, and blue dots, the screen
gets lighter, until you reach the full intensity of all three primary colors,
which is white. This is known as additive color synthesis. A blank piece of
paper is white. As you place dots of cyan, magenta, and yellow closer
together, and on top of each other, the color intensity gets darker, until
you reach full ink coverage with all three colors, which is black.
This is known as subtractive color synthesis. It is also interesting to note,
that if you mix any two of the three primary colors of additive color
synthesis, you get the set of secondary colors: ( yellow = r + g ),
( magenta = r + b ), and ( cyan = g + b ). The secondary colors of additive
color synthesis are the primary colors of subtractive color synthesis, and
visa-versa.
 
Note: Even palette mode, 8 bit per pixel bitmaps have 16.8 million possible 
color variations, but only 256 of them can appear in the same image at once.

Let's say one pixel of your image is a sort of light olive green,
and the "R, G, B" values for this pixel are:
  
  Red = 118      Green = 178      Blue = 89

That means that the printer will look at this color as follows:
   
   Cyan = 255 - 118 (red)   = 137
Magenta = 255 - 178 (Green) =  77
 Yellow = 255 -  89 (Blue)  = 116

If enlarged to exactly 16 times, it will be printed as a block of 256 dots,
16 by 16 with exactly 137 cyan dots, 77 magenta dots, and 116 yellow dots,
arranged in some manor determined by the screening method used in the
printer driver.

Some color printer drivers come with so called "screen matched color" 
options. These are intended to more closely match the colors you would see
on your monitor. They will put a more complex curve into the simple "R,G,B"
to "C,M,Y" conversions. Go ahead and use them if you like.

But, when printing images that only contain the seven fundamental colors,
where fine detail is essential, such as line drawings, it is best to print
at printer resolution for the most predictable results. Do not use screen
matching color routines because parts of the picture will disappear.
Solid lines become dotted lines etc..

The seven possible full intensity colors are:

             Red     Green    Blue
Black         0        0       0
Red          255       0       0  
Green         0       255      0
Blue          0        0      255
Cyan          0       255     255
Magenta      255       0      255
Yellow       255      255      0

where red, green, and blue are the color values stored in your bitmap image.
White, which is the absence of any ink, is represented by 
255, 255, 255 for the corresponding red, green, and blue values. 

"PaletteFormula_09_8", a procedure found in "BMP_8.RLO", creates a palette 
with these 8 colors repeated 32 times.
  
Dither, halftone, dot screen, error diffusion, stochastic raster image
processing, etc. are all methods of calculating how to place the primary
colored dots in areas to simulate the more complex, non fundamental colors,
hues, and shades. When printing pictures with lots of color variation
as mentioned above, with enlargement to enhance the color depth, you
will probably get the best results using a non-pattern method.
That is, random, error diffusion, stochastic, or whatever it is called
in your printer driver. When printing images that only contain the seven
fundamental colors without screen matching color correction, the screening
method should be irrelevant. Choose the simplest method for your computer
to figure. This would be pattern, or halftone. It will be much faster.
If you have no selection to make, then all you have is a pattern method.

If you do have a color ink jet printer, and you still haven't tried
coated paper yet, I highly recommend it. It might cost as much as
13 cents per page, but if you select the coated paper option in the
printer driver, it requires less ink to make a super vivid color picture.
