Subject:
|
Re: Substitute Colors for Dithered Colors?
|
Newsgroups:
|
lugnet.cad.dev
|
Date:
|
Mon, 2 Jul 2001 01:13:22 GMT
|
Viewed:
|
413 times
|
| |
|
|
Erik Olson wrote...
> I'm wondering how to treat dithered colors (LDRAW 0x0100 to 0x01ff, see
> FAQ). Short of implementing a dithered texture--which would preserve that
> old-timey look--I'm seeking a conversion function.
>
> My first guess is that the perceptual equivalent of a dithered color is the
> average of its RGB components. Good enough or not?
I use the average of the two colors' RGB. Try it out in L3Lab by toggling
the "Dither or blend colord 256-511" button in the toolbar.
Here is the code I use for color decoding:
/* Return -1 on invalid LDraw color. rgb may be NULL for test only. */
int Color2rgb(long Color, float rgb[], int *IsTransparent)
{
int c1;
int c2;
if (rgb)
rgb[0] = rgb[1] = rgb[2] = 0.5; /* default */
if (IsTransparent)
*IsTransparent = 0; /* Assume opaque (non-transparent */
/* if ((0 <= Color && Color <= 15) || (32 <= Color && Color <= 47)) */
if (0 <= Color && Color <= 63 && !(Rgbs[(int) Color] & 0x80000000)) /* (int) is for TurboC */
{
if (rgb)
{
rgb[0] = GetRValue(Rgbs[(int) Color]) / 255.0; /* (int) */
rgb[1] = GetGValue(Rgbs[(int) Color]) / 255.0; /* is for */
rgb[2] = GetBValue(Rgbs[(int) Color]) / 255.0; /* TurboC */
}
if (IsTransparent && Color >= 32)
*IsTransparent = 1;
return 0;
}
if (256 <= Color && Color <= 511)
{
if (rgb)
{
c1 = ((int) Color) & 15; /* (int) is for TurboC */
c2 = (((int) Color) >> 4) & 15; /* (int) is for TurboC */
rgb[0] = (GetRValue(Rgbs[c1]) + GetRValue(Rgbs[c2])) / (2 * 255.0);
rgb[1] = (GetGValue(Rgbs[c1]) + GetGValue(Rgbs[c2])) / (2 * 255.0);
rgb[2] = (GetBValue(Rgbs[c1]) + GetBValue(Rgbs[c2])) / (2 * 255.0);
}
return 0;
}
/* switch (Color) -- TurboC (K&R1) only accepts int */
c1 = (unsigned char) (Color >> 24);
switch (c1)
{
case 3:
if (IsTransparent)
*IsTransparent = 1;
/* Fall through */
case 2:
if (rgb)
{
rgb[0] = ((Color >> 16) & 255) / 255.0;
rgb[1] = ((Color >> 8) & 255) / 255.0;
rgb[2] = (Color & 255) / 255.0;
}
return 0;
case 4:
if (rgb)
{
rgb[0] = (((Color >> 20) & 15) + ((Color >> 8) & 15)) / (2 * 15.0);
rgb[1] = (((Color >> 16) & 15) + ((Color >> 4) & 15)) / (2 * 15.0);
rgb[2] = (((Color >> 12) & 15) + (Color & 15)) / (2 * 15.0);
}
return 0;
case 5: /* Use 0x05RGB000 */
Color >>= 12;
/* Fall through */
case 6: /* Use 0x06000RGB */
if (rgb)
{
rgb[0] = ((Color >> 8) & 15) / 15.0;
rgb[1] = ((Color >> 4) & 15) / 15.0;
rgb[2] = (Color & 15) / 15.0;
}
if (IsTransparent)
*IsTransparent = 1;
return 0;
case 7:
if (rgb)
{
rgb[0] = rgb[1] = rgb[2] = 0.0; /* Invisible! */
}
return 0;
}
return -1;
}
Rgbs is an array holding the RGB values for the first 64 colors:
COLORREF Rgbs[64] =
{
RGB(0, 0, 0),
RGB(0, 0, 170),
RGB(0, 170, 0),
RGB(0, 170, 170),
RGB(170, 0, 0),
RGB(170, 85, 127),
...
0x80000000, /* Color 16 is illegal here */
...
};
COLORREF is a Windows thing:
typedef unsigned char BYTE;
typedef unsigned short WORD;
typedef unsigned long DWORD;
typedef DWORD COLORREF;
#define RGB(r,g,b) ((COLORREF)(((BYTE)(r)|((WORD)((BYTE)(g))<<8))|(((DWORD)(BYTE)(b))<<16)))
#define GetRValue(rgb) ((BYTE)(rgb))
#define GetGValue(rgb) ((BYTE)(((WORD)(rgb)) >> 8))
#define GetBValue(rgb) ((BYTE)((rgb)>>16))
i.e. the color is encoded 0x00BBGGRR
I set a bit (0x80000000) for illegal colors, such as 16, 24, 29 etc.
Also you may find this table useful:
// Color24 has edge colors (contrast colors/complement colors) for colors 0..15
// Complementing is not reversible for colors 6,7,14,15.
// i.e. Color24[Color24[6]] == 8
int Color24[32] = {
8, 9, 10, 11, 12, 13, 0, 8,
0, 1, 2, 3, 4, 5, 8, 8,
24, 2, 8, 6, 22, 8, 20, 9,
0, 4, 13, 2, 6, 15, 15, 15
};
/Lars (leaving for vacation in Norway :-)
|
|
Message has 1 Reply:
 | | Re: Substitute Colors for Dithered Colors?
|
| Wow, Lars, that was a lot of code to support r = (r1+r2)/2. The obvious hypothesis would say that the eye performs spatial integration on the pixels, so therefore values are averaged. I guess I can try it on my eyes with L3Lab then. I looked in (...) (23 years ago, 2-Jul-01, to lugnet.cad.dev)
|
Message is in Reply To:
| | Substitute Colors for Dithered Colors?
|
| Hi, I'm wondering how to treat dithered colors (LDRAW 0x0100 to 0x01ff, see FAQ). Short of implementing a dithered texture--which would preserve that old-timey look--I'm seeking a conversion function. My first guess is that the perceptual equivalent (...) (23 years ago, 30-Jun-01, to lugnet.cad.dev)
|
5 Messages in This Thread:
  
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
