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PixelInteger.c
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1992-06-16
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54 lines
/*
Proper Treatment of Pixels as Integers
by Alan Paeth
from "Graphics Gems", Academic Press, 1990
*/
#define Min code[2]
#define Med code[1]
#define Max code[0]
#define NCODE 3
/*
* A call to getplanes of the form:
* getplanes(&red, &green, &blue, 256, "grb");
*
* fills the first three integer pointers with (near) identical
* values which maximize red*green*blue <= 256. The final parameter
* string defines tie-break order, here green>=red>=blue (the usual
* default). The present code procedure calls "err(string, arg)"
* given bad parameters; it is a simple task to rewrite the code as
* a function which returns a success/failure code(s), as needed.
*
* In the example given above the code fills in the values
* red = 6, green = 7, blue = 6.
*/
getplanes(r, g, b, n, bias)
int *r, *g, *b;
char *bias;
{
int i, code[NCODE];
if(strlen(bias) != NCODE )
err("bias string \"%s\" wrong length",bias);
Min = Med = Max = 0;
*r = *g = *b = 0;
while(Min*Min*Min <= n) Min++;
Min--;
while(Med*Med*Min <= n) Med++;
Med--;
Max = n/(Min*Med);
for( i = 0; i < NCODE; i++ )
{
switch(bias[i])
{
case 'r': case 'R': *r = code[i]; break;
case 'g': case 'G': *g = code[i]; break;
case 'b': case 'B': *b = code[i]; break;
default: err("bad bias character: \'%c\'",bias[i]); break;
}
}
if (!(*r && *g && *b)) err("bias string \"%s\" deficient", bias);
}