Convert to BW

vandana7

How to convert grayscale image(.tif )to black & white ?

enhzflep

To do that, you just need to de-saturate the image. The RGB colour-space does not easily lend itself to this operation, and the HSL colour model is far more useful here. In an entirely non optimized method, you would: Repeat loop for all pixels in source image (1) convert pixel RGB to HSL (2) drop the S value to 0 (3) convert back to RGB (4) dump the converted pixel back Here's some routines for colour-space conversion:

// Input: h, s, v in range [0..1]
// Outputs: r, g, b in range [0..1]
void hsvToRgb(float h, float s, float v, float *r, float *g, float *b)
{
int i;
float aa, bb, cc, f;

 if (s == 0.0) // greyscale
    \*r = \*g = \*b = v;
 else
 {
     if (h == 1.0) h = 0.0;
     h \*= 6.0;
     i = floor(h);
     f = h - (float)i;
     aa = v \* (1.0 - s);
     bb = v \* (1.0 - (s \* f));
     cc = v \* (1.0 - (s \* (1.0 - f)));
     switch(i)
     {
       case 0: \*r = v; \*g = cc; \*b = aa; break;
       case 1: \*r = bb; \*g = v; \*b = aa; break;
       case 2: \*r = aa; \*g = v; \*b = cc; break;
       case 3: \*r = aa; \*g = bb; \*b = v; break;
       case 4: \*r = cc; \*g = aa; \*b = v; break;
       case 5: \*r = v; \*g = aa; \*b = bb; break;
     }
 }

}

#define myMin(a,b) (a
#define myMax(a,b) (a>b?a:b)
#define noHue 0

// Inputs: r, g, b in range [0..1]
// Outputs: h, s, v in range [0..1]
void rgbToHsv(float r, float g, float b, float *h, float *s, float *v)
{
float max = myMax(r, myMax(g, b)), min = myMin(r, myMin(g, b));
float delta = max - min;

 \*v = max;
 if (max != 0.0)
    \*s = delta / max;
 else 
      \*s = 0.0;
 if (\*s == 0.0) \*h = noHue;
 else
 {
     if (r == max)
        \*h = (g - b) / delta;
     else if (g == max)
        \*h = 2 + (b - r) / delta;
     else if (b == max)
        \*h = 4 + (r - g) / delta;
     \*h \*= 60.0;
     if (\*h < 0) \*h += 360.0;
     \*h /= 360.0;
 }

}

I'll leave it to you to make them work with RGB values in the range [0..255]

Nibu babu thomas

enhzflep wrote:

Here's some routines for colour-space conversion:

These functions does the same, right? ColorRGBToHLS ColorHLSToRGB

Nibu thomas Microsoft MVP for VC++ Code must be written to be read, not by the compiler, but by another human being. Programming Blog: http://nibuthomas.wordpress.com

enhzflep

:-\ After looking at: http://msdn.microsoft.com/en-us/library/bb773851(VS.85).aspx[^] It would certainly appear so. In fact, they'd be even better, since they deal with WORDs instead of floats. That'll teach me for using a 11 year old API help file.. Thanks for the better solution.

Nibu babu thomas

enhzflep wrote:

That'll teach me for using a 11 year old API help file..

:)

Nibu thomas Microsoft MVP for VC++ Code must be written to be read, not by the compiler, but by another human being. Programming Blog: http://nibuthomas.wordpress.com