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Forum Index : Microcontroller and PC projects : Color Wheels

Author Message
William Leue
Senior Member

Joined: 03/07/2020
Location: United States
Posts: 259
Posted: 07:51pm 25 Aug 2020
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Here is a short program that displays color wheels for the different color memory modes. There are 4 wheels which together cover most of the color gamut for each color memory mode.

It is interesting and instructive to see how the wheels change as you move from 8 to 12 and then 16-bit color. Whereas 8-bit color shows the expected color quantization and some false contouring, by the time you get to 16 bits the color shading is almost completely smooth and free from false contours.

No surprises there, and of course 8 bits is plenty for almost all games.

-Bill



' Color charts for the 3 color depths.
' Rev 1.0.0 William M Leue 8/21/2020

option default integer

const NMODES = 4
const CRADIUS = 125
const HMARGIN = 50
const VMARGIN = 30
const CSEP = 30

do
 ok = 1
 input "Select Color Bits (8, 12, or 16): ", ans$
 b = val(ans$)
 if b <> 8 and b <> 12 and b <> 16 then
   print "unsupported color bits - try again"
   ok = 0
 end if
loop until ok = 1

mode 1, b
cls
text HMARGIN+2*CRADIUS+CSEP/2, 280, str$(b) + "-bit Colors", C

DrawColorWheels

xx$ = INKEY$
text 10, 585, "Press any Key to Exit"
do : loop until INKEY$ <> ""
end

' Draw 4 color wheels for the current color bit mode:
' Top Left wheel: Brightness = 1, Saturation decreases toward center
' Top Right wheel: Saturation = 1, Brightness decreases toward center
' Bottom Left wheel: Brightness and Saturation both decrease.
' Bottom Right wheel: Grayscale.
sub DrawColorWheels
 local cx, cy, x, y, sr
 local integer r, g, b
 local float hue, sat, brt, fr
 local col

 cx = HMARGIN+CRADIUS
 cy = VMARGIN+CRADIUS
 text cx, VMARGIN-2, "V=1.0, S=1.0->0.0", CB
 for sr = CRADIUS-1 to 1 step -1
   fr = CRADIUS-1  
   sat = sr/fr
   for hue = 0.0 to 359.5 step 0.5
     x = cx + sr*cos(rad(hue))
     y = cy - sr*sin(rad(hue))
     HSV2RGB hue, sat, 1.0, r, g, b
     col = RGB(r, g, b)
     box x, y, 2, 2,, col, col
   next hue      
 next sr

 cx = cx + CRADIUS + CSEP + CRADIUS
 text cx, VMARGIN-2, "S=1.0,V=1.0->0.0", CB
 for sr = CRADIUS-1 to 1 step -1
   fr = CRADIUS-1  
   brt = sr/fr
   for hue = 0.0 to 359.5 step 0.5
     x = cx + sr*cos(rad(hue))
     y = cy - sr*sin(rad(hue))
     HSV2RGB hue, 1.0, brt, r, g, b
     col = RGB(r, g, b)
     box x, y, 2, 2,, col, col
   next hue      
 next sr


 cx = HMARGIN+CRADIUS
 cy = VMARGIN+3*CRADIUS + CSEP
 text cx, cy-CRADIUS-2, "S=1.0->0.0,V=1.0->0.0", CB
 for sr = CRADIUS-1 to 1 step -1
   fr = CRADIUS-1  
   sat = sr/fr
   brt = sr/fr
   for hue = 0.0 to 359.5 step 0.5
     x = cx + sr*cos(rad(hue))
     y = cy - sr*sin(rad(hue))
     HSV2RGB hue, sat, brt, r, g, b
     col = RGB(r, g, b)
     box x, y, 2, 2,, col, col
   next hue      
 next sr


 cx = cx + CRADIUS + CSEP + CRADIUS
 text cx, cy-CRADIUS-2, "Grayscale", CB
 for sr = CRADIUS-1 to 1 step -1
   fr = CRADIUS-1  
   brt = sr/fr
   for hue = 0.0 to 359.5 step 0.5
     x = cx + sr*cos(rad(hue))
     y = cy - sr*sin(rad(hue))
     HSV2RGB hue, 0.0, brt, r, g, b
     col = RGB(r, g, b)
     box x, y, 2, 2,, col, col
   next hue      
 next sr

end sub

sub PrintMsg msg$
 text 10, 550, SPACE$(50)
 text 10, 550, msg$
end sub

sub GetInput msg$, ans$
 PrintMsg msg$
 input ans$
end sub

' Convert an RGB color value to its HSV equivalent
' the RGB values must be in range 0..255; the S and V values will
' be in range 0..1; the H value will be in range 0..360
sub RGB2HSV r, g, b, h, s, v
 local rp, cmax, cmin, delta

 rp = r/255.0 : gp = g/255.0 : bp = b/255.0
 cmax = max(rp, max(gp, bp))
 cmin = min(rp, min(gp, bp))
 delta = cmax - cmin
 if delta = 0 then
   h = 0
 else if cmax = rp then
   h = 60*(((gp-bp)/delta) MOD 6)
 else if cmax = gp then
   h = 60*(((bp-rp)/delta) + 2)
 else
   h = 60*(((rp-gp)/delta) + 4)
 end if
 if cmax = 0 then
   s = 0
 else
   s = delta/cmax
 end if
 v = cmax
end sub

' Convert an HSV value to its RGB equivalent
' The S and V values must be in range 0..1; the H value must
' be in range 0..360. The RGB values will be in range 0..255.
sub HSV2RGB h as float, s as float, v as float, r as integer, g as integer, b as integer
 local float hh, f, p, q, t, x, c, rp, gp, bp
 local integer i

 c = v*s
 hh = h/60.0
 i = int(hh)
 f = hh - i
 p = v*(1-s)
 q = v*(1-s*f)
 t = v*(1-s*(1-f))
 x = c*(1.0 - hi MOD 2 - 1)
 
 select case i
   case 0
     rp = v : gp = t : bp = p
   case 1
     rp = q : gp = v : bp = p
   case 2
     rp = p : gp = v : bp = t
   case 3
     rp = p : gp = q : bp = v
   case 4
     rp = t : gp = p : bp = v
   case 5
     rp = v : gp = p : bp = q
 end select
 r = rp*255 : g = gp*255 : b = bp*255
end sub

' function to return an RGB color, given the h, s, and v
' values as input parameters. The S and V values must be
' in the range 0..1; the H value must be in the range
' 0..360. The output value will be a 24-bit RGB color.
function GetRGBColor(h, s, v)
 local r, g, b, c

 HSV2RGB h, s, v, r, g, b
 c = RGB(r ,g, b)
 GetRGBColor = c
end function
 
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