Grey Scale Bitmaps
Grey scale is necessary for compatibility with Qbasic's legacy SCREEN modes when viewing 24/32 bit bitmaps! You may also desire grey scale images for aesthetic or artistic reasons.
- Set each color attribute's RGB intensities to the same value while incrementing the attribute values and intensity levels.
- Don't exceed 63 when using OUT in legacy screen modes 12 or 13. Screens 7 and 9 use DAC color settings.
- Then set the color attributes to reflect the number of colors available in that legacy screen mode.
- 24/32 bit do not use color attributes, so the intensity levels must be set to an average for all three.
SUB TrueColor12 'Screen 12 greyscale of 24 bit 'code by Bob Seguin IF BMP.PWidth * 3) MOD 4) THEN ZeroPAD$ = SPACE$((4 - ((BMP.PWidth * 3) MOD 4))) END IF n = 3 FOR Colr = 0 TO 15 '16 colors OUT &H3C8, Colr OUT &H3C9, n 'color intensities are each equal in grey scale OUT &H3C9, n OUT &H3C9, n n = n + 4 'increment intensities. maximum intensity = 63 NEXT Colr y = BMP.PDepth - 1: o$ = " " GET #1, BMP.Offset, o$ R$ = " ": G$ = " ": B$ = " " DO x = 0 'set image to left of screen DO GET #1, , B$ GET #1, , G$ GET #1, , R$ red = ASC(R$) 'intensities from 0 to 255 grn = ASC(G$) blu = ASC(B$) average = (red + grn + blu) \ 48 'divide by 16 colors and divide by 3 for average PSET (x, y), average '255 * 3 divided by 16 = maximum color of 15 x = x + 1 LOOP WHILE x < BMP.Pwidth GET #1, , ZeroPAD$ 'move up one row from bottom y = y - 1 LOOP UNTIL y = -1 END SUB
SUB TrueColor13 'Screen 13 greyscale of 24 bit 'code by Bob Seguin IF ((BMP.PWidth * 3) MOD 4) <> 0 THEN ZeroPAD$ = SPACE$((4 - ((BMP.PWidth * 3) MOD 4))) END IF FOR Colr = 0 TO 255 STEP 4 '63 different intensities FOR Reps = 0 TO 3 'set 3 colors at a time OUT &H3C8, Colr + Reps OUT &H3C9, n 'color intensities are each equal in grey scale OUT &H3C9, n OUT &H3C9, n NEXT Reps n = n + 1 'increment intensities. maximum = 63 NEXT Colr y = BMP.PDepth - 1: o$ = " " GET #1, BMP.Offset, o$ 'offset + 1 immediately after header R$ = " ": G$ = " ": B$ = " " DO x = 0 'set image to left side of screen DO GET #1, , B$ GET #1, , G$ GET #1, , R$ red = ASC(R$) grn = ASC(G$) blu = ASC(B$) average = (red + grn + blu) \ 3 'divide by 3 for average as colors match intensities PSET (x, y), average '3 * 255 divided by 3 = maximum color attribute of 255 x = x + 1 LOOP WHILE x < BMP.PWidth GET #1, , ZeroPAD$ 'skip padder if used y = y - 1 'move up one row from bottom LOOP UNTIL y = -1 END SUB
SUB TrueGreyScale 'convert a 24 bit bitmap image to grey scale IF ((BMP.PWidth * 3) MOD 4) <> 0 THEN ZeroPAD$ = SPACE$((4 - ((BMP.PWidth * 3) MOD 4))) END IF y = BMP.PDepth - 1: o$ = " " GET #1, BMP.Offset, o$ 'offset + 1 immediately after header R$ = " ": G$ = " ": B$ = " " DO x = 0 'set image to left side of screen DO GET #1, , B$ GET #1, , G$ GET #1, , R$ red = ASC(R$) grn = ASC(G$) blu = ASC(B$) average = (red + grn + blu) \ 3 'divide by 3 for average as colors match intensities PSET (x, y), _RGB32(average, average, average) 'maximum color intensity = 255 x = x + 1 LOOP WHILE x < BMP.PWidth GET #1, , ZeroPAD$ 'skip padder if used y = y - 1 'move up one row from bottom LOOP UNTIL y = -1 END SUB
- To tint a SCREEN 12 or 13 greyscale image, keep the palette intensity settings of 1 or 2 colors less than the others.
FOR Colr = 0 TO 255 STEP 4 '63 different intensities FOR Reps = 0 TO 3 'set 3 colors at a time OUT &H3C8, Colr + Reps OUT &H3C9, n - tint 'decrease color intensities of red and green OUT &H3C9, n - tint OUT &H3C9, n 'higher blue intensity will blue the image NEXT Reps n = n + 1 'increment intensities. maximum = 63 IF n > 5 THEN tint = 5 'keep red and green intensity values above 0! NEXT Colr
- In 24/32 bit SCREENs, subtract some intensity from one or two of the 3 image pixel settings.
DO GET #1, , B$ GET #1, , G$ GET #1, , R$ red = ASC(R$) grn = ASC(G$) blu = ASC(B$) average = (red + grn + blu) \ 3 'divide by 3 for average as colors match intensities IF average > 5 THEN tint = 5 ELSE tint = 0 PSET (x, y), _RGB32(average - tint, average - tint, average) 'maximum color intensity = 255 x = x + 1 LOOP WHILE x < BMP.PWidth
- You could keep the red and green intensity settings higher than blue to yellow, brown, or antique the image too.
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