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190 Grays

==================== 190 gray levels sounds like a strange number, especially since the video modes we are using are capable of 256 colors from a palette of 262,144 different colors. The challenge comes in creating a black and white palette that will maximize your monitor's display capabilities. As JIMSAIP only deals in monochromatic images, we speak of gray levels as representing what your video card/monitor can realize as different levels of light intensity.

The manner in which your video card/monitor function is to create spots of light (pixels) on the monitor screen using three electron beams, one each for the colors red, blue, and green. Each beam can be adjusted from minimum to maximum intensity in 64 steps. If each beam has equal intensity, the resulting color is white although it's brightness depends upon the total intensity of the three beams. If we represent a given combination of intensities as an ordered set of three numbers such as (r,b,g) where the letters represent numbers ranging from 0 to 63 of each of the three color beams respectively, we can see what is going on.

To start with, with this combination only 64 different intensities of white can be realized (designated 'shades of gray'). Thus, we could have

Gray Level     Combination     Total Intensity

0               (0,0,0)           0

1               (1,1,1)           3

2               (2,2,2)           6

.

.

62              (62,62,62)        186

63              (63,63,63)        189

Thus we see the total intensity ranges from 0 (black) to 189 (white) in 64 steps of 3. In creating a palette of 256 levels using these 64 possible shades we would have,

Level           Combination       Intensity

0               (0,0,0)           0

1               (0,0,0)           0

2               (0,0,0)           0

3               (0,0,0)           0

4               (1,1,1)           3

5               (1,1,1)           3

6               (1,1,1)           3

7               (1,1,1)           3

.

.

252             (63,63,63)        189

253             (63,63,63)        189

254             (63,63,63)        189

255             (63,63,63)        189

BUT, we can do better! If we accept a little bit of color, we can fill in the gaps between the intensity steps with 'almost' white choices and get a finer resolution in our intensity scale. Thus we could use

(0,0,1) or (0,1,0) or (1,0,0) to achieve a 'nearly white' intensity of 1.

Likewise, we could use

(0,1,1) or (1,0,1) or (1,1,0) to achieve a 'nearly white' intensity of 2.

It doesn't make any difference which of the choices is selected to represent the given intensity level. But, by continuing in this fashion, we can fill in the total intensity range of 0 to 189 with equally spaced steps (of 1) to achieve 190 'gray' levels. This is the scheme JIMSAIP uses and we don't believe a finer gray level resolution can be had using the video choices available here (which use 6 bit DACs to control the electron beams).