RGB to HSV Conversion
Colors
in RGB space can be converted to HSV (
1.
Figure 1.
2. Saturation
is the amount of white light mixed with
3. Value determines the lightness and the darkness of the color. Value 255 is the lightest and 0 is the darkest color. Table 1. Shows some RGB and HSV values of well known colors.
Table 1. Some HSV converted colors
|
Red
R: 255 H: 240.00º
G: 0 S: 1.00
B: 0 V: 255
|
Blue
R: 0 H: 0.0º
G: 0 S:
1.00
B: 255 V: 255
|
Green
R: 0 H: 120.0º
G: 255 S: 1.00
B: 0 V: 255
|
Yellow
R: 0 H:
180.0º
G: 255 S: 1.00
B: 255 V: 255
|
|
Pink
R: 255 H: 300.0º
G: 0 S: 1.00
B: 255 V: 255 |
????
R: 0 H:
60.0º
G: 255 S: 1.00 B: 255 V: 255 |
Sea Blue
R: 225 H: 32.57º
G: 145 S: 1.00 B: 50 V: 225 |
R: 0 H:
209.88º
G: 128 S: 1.00 B: 255 V: 255
|
C Source Code
Here is a procedure calculating HSV values of a number of colors presented in BMP 24-bit formatted images.
{
long i, width, height, R, G, B;
long Value, tmp;
double Saturation, Hue, Cr, Cg, Cb;
long **img_data;
BMPHEADER BmpHdr;
FILE *f, *f_text;
char FileNM[20];
//
//
CheckBmpComp("i000.bmp", &BmpHdr);
f_text = fopen("compare_result.txt","w");
fprintf(f_text, "Here are the RGB ---> HSV convertion results\n");
fprintf(f_text, "----------------------------------------------\n");
for(i=0;i<8;i++)
{
Generate_File_Name(i, "i", FileNM, 2);
f = fopen(FileNM,"rb");
fseek(f, BmpHdr.BmpOffset, SEEK_SET);
R = (unsigned char)fgetc(f);
G = (unsigned char)fgetc(f);
B = (unsigned char)fgetc(f);
/// VALUE
// find maximum
if ( (R >= G) && (R >= B))
Value = R;
else if ( (G >= R) && (G >= B))
Value = G;
else if ( (B >= G) && (B >= R))
Value = B;
/// SATURATION
// find minimum
if ( (R <= G) && (R <= B))
tmp = R;
else if ( (G <= R) && (G <= B))
tmp = G;
else if ( (B <= G) && (B <= R))
tmp = B;
if (Value == 0)
Saturation = 0;
else
Saturation = ((double)Value - (double)tmp)/(double)Value;
/// HUE
if (Saturation == 0)
Hue = -1;
else
{
Cr = ((double)Value-(double)R)/((double)Value-(double)tmp);
Cg = ((double)Value-(double)G)/((double)Value-(double)tmp);
Cb = ((double)Value-(double)B)/((double)Value-(double)tmp);
if (R == Value)
Hue = Cb - Cg;
if (G == Value)
Hue = 2 + Cr - Cb;
if (B == Value)
Hue = 4 + Cg - Cr;
Hue *= 60;
if (Hue < 0)
Hue +=360;
}
fprintf(f_text, "R:%3d G:%3d B:%3d ----> H:%3.2f S:%3.2f V:%3d\n", R, G, B, Hue, Saturation, Value);
fclose(f);
}
fclose(f_text);
return 0;
}