
OSD Generator Operation (Continued)
FOUR COLOR FONT AS TWO 2-COLOR
Using a 4 color character as two 2 color characters is
achieved by careful assignment of the four colors. When two
2 color characters are combined, there will be four pixel
colors:
Color 0: Those
that
are
background
pixels
for
both
characters,
Color 1: Those that are foreground pixels in character one
and background pixels in character two,
Color 2: Those that are foreground pixels in character two
and background pixels in character one,
Color 3: Those
that
are
foreground
pixels
for
both
characters.
In order to identify which pixels are which, both characters
should be drawn in one character cell using the same back-
ground color, and different background colors. In
Figure 17,both “A” and a “B” are drawn separately, then superimposed,
with the final 4 color character on the right. Comparing it to
the list of colors, it is seen that white is color 0, black is color
1, blue is color 2 and red is color 3. (These particular four
colors were chosen for clarity).
Figure 18 shows the composite four color character in the
center and the palette choices on the left and the right which
result in the display of the two original characters.
To display character 1, which has a foreground color 1,
character 2 must be hidden by setting its foreground color
(color 2) to equal the background. Color 3 (common pixels)
must be set to the desired foreground (color 1). In this case,
color 0 and color 2 are black and color 1 and color 3 are
white.
To display character 2, set color 1 = color 0 (to hide charac-
ter 1) and color 3 = color 2. Other than this, there is no
restriction on the choice of the actual colors used.
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FIGURE 16. Four-Color Character
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FIGURE 17. Four Color Character asa2x2 Color
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