Black is truly an Ink or Toner Hog! Large amounts of any color for that matter
are.  The more white or pail color you have in an image, the less ink it
requires when printing.

In the old world of color book printing, all of Jims statements are correct.
There are exceptions however, such as was with the Compendium of Seashells.
All of the color plates were printed 4 color CMY & Black (gray scale), then the
text was printed as a separate film over all the finished photo graphic work
allowing for a true black only ink for all the text.  Dutton for saw this issue
and choose an additional printing step.  This also allowed for the changes and
corrections made in some captions found in the EP Dutton Second Printing
(revised) 1983 edition.  As such all they had to change was a page of black
text film when a change was made, which is a nominal cost when solid black,
verses a color separation which is 4 films (CMYB) and more costly per film as
well time.

In a graphic for a computer, Black is measured in a Grey Scale and / or Hue
saturation, in other words there is more than just black to the image.  When
you do a background fill selecting black, it is for all practical purposes 1:1
black ink, but soon as you save the image as a jpg or other compressible image
it looses the pure black quality.  As such I work with most of my graphics as a
bitmap (BMP) which is not compressed and is easily 3 to 50 times the file size
of a compressed image.

The amount of memory a color (or file) takes up is relative not to the color
but to the setting the file has... i.e. color scale. 16 color, 256, 16,000, 32
Mil etc... which means the color depth matrix gets larger and larger, also it
the DPI (dots per inch) and resolution.  Then again, when you save it as a
compressed file, that formula is chopped up.

This is very similar to what is referred to as video band width (as it relates
to signal going to your computer monitor), which is a formula based upon:
Resolution, frequency, number of colors (plus distance and cable type).  i.e. -
the relevance being, Resolution and number of colors representing amount of
information contained in an image.

But, to refer back to Jim, being that he is in the printing and publishing
industry, he is far more fluent in this topic and technology than I.

As another note generically speaking:
* In base printers ink colors are a measure of a solid.  Rendering as: cyan,
magenta and yellow (a blue, off red, and yellow) plus black for gray scale.
(CMY or CMYB)
* For your computer monitor it is measured as an emission of light, rendering
as Red, Green and Blue or "RGB".

Best Regards,
Leslie Allen Crnkovic
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>I have been told that black is a memory hog.
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Hi Andrew,
As far as compressing images, no color is better than any other as far as
gobbling up space (or megabytes). Possibly this information comes in a
roundabout way through the printing process. Here, black is definitely a bear
to deal with. The reason is that true black is really black, cyan, magenta and
yellow (typically 100% black ink, 50% cyan, 40% red and 30% yellow), making it
far more costly that simple reds, blues or yellows. Printers cringe when they
see too many solid blacks.  But in terms of digital data, a solid color is the
simplest to compress, be it white, red, blue, black, etc.
Best regards,
Jim