It's a code of function changing kontrast of bitmap. But it don't work that I want. Maybe someone saw how loooks changing contrast in PhotoShop. I want to reach the same effect... In attaching image I show how it works in PS (right) in my function (center). On the left is source image... Any ideas how to reach effect like in PhotoShop ?
Code:
#include <windows.h>
#include "epfEngine.h"
#include <complex>
static unsigned char TransLut[256];
void build_lookup_table ( int contr )
{
float step,step_value;
for (int i=0; i < 256; i++)
TransLut[i] = i;
if (contr > 0)
{
unsigned int MinBin = contr;
unsigned int MaxBin = 255 - contr;
step = sqrt((double)contr)/contr;
step_value = 0.0;
for ( i = 0; i < MinBin; i++)
{
TransLut[i] = (unsigned char)step_value;
step_value += step;
}
step = 256.0f / (float)(MaxBin-MinBin);
for ( i = MinBin; i <= MaxBin; i++)
{
if (step_value > 255.0f)
{
step_value = 255.0f;
step = 0.0f;
}
TransLut[i] = (unsigned char)step_value;
step_value += step;
}
for ( i = MaxBin + 1; i < 256; i++)
TransLut[i] = 255;
}
else
{
if (contr<0)
{
step = (256.0+(float)(contr*2))/256.0;
step_value = (float)contr * -1.0;
for (i = 0;i < 256; i++)
{
TransLut[i] = (unsigned char)step_value;
step_value += step;
}
}
}
}
BOOL epfChangeBitmapContrast(HBITMAP * phBitmap, int iCount)
{
BITMAP bm;
BYTE * pBits;
RGBQUAD * pRgb;
WORD wByteCount;
int i, iPixels, gray;
build_lookup_table(iCount);
// Take BITMAP structure from HBITMAP
GetObject(*phBitmap, sizeof(BITMAP), &bm);
// Calculate bytes to read
wByteCount = bm.bmHeight * (2 * ((bm.bmWidth * bm.bmBitsPixel + 15) / 16));
// Alocate momory for bits od pixels and get pointers
pBits = (BYTE *) malloc(wByteCount);
GetBitmapBits(*phBitmap, wByteCount, pBits);
// Convert pointer to byte to pointer to RGBQUAD
pRgb = (RGBQUAD *) pBits;
// Operate on pixel's colors
iPixels = wByteCount / (bm.bmBitsPixel / 8);
for(i = 0; i < iPixels; i++, pRgb++)
{
gray = (pRgb->rgbRed + pRgb->rgbGreen + pRgb->rgbBlue) / 3;
int k = TransLut[gray]-gray;
pRgb->rgbRed = min(pRgb->rgbRed + k, 255);
pRgb->rgbGreen = min(pRgb->rgbGreen + k, 255);
pRgb->rgbBlue = min(pRgb->rgbBlue + k, 255);
}
SetBitmapBits(*phBitmap, wByteCount, pBits);
return TRUE;
}