protected override unsafe void ProcessFilter( UnmanagedImage image, Rectangle rect )
{
int pixelSize = ( image.PixelFormat == PixelFormat.Format8bppIndexed ) ? 1 :
( image.PixelFormat == PixelFormat.Format24bppRgb ) ? 3 : 4;
int startX = rect.Left;
int startY = rect.Top;
int stopX = startX + rect.Width;
int stopY = startY + rect.Height;
int stride = image.Stride;
int offset = stride - rect.Width * pixelSize;
int numberOfPixels = ( stopX - startX ) * ( stopY - startY );
// check image format
if ( image.PixelFormat == PixelFormat.Format8bppIndexed )
{
// grayscale image
byte* ptr = (byte*) image.ImageData.ToPointer( );
// allign pointer to the first pixel to process
ptr += ( startY * stride + startX );
// calculate histogram
int[] histogram = new int[256];
for ( int y = startY; y < stopY; y++ )
{
for ( int x = startX; x < stopX; x++, ptr++ )
{
histogram[*ptr]++;
}
ptr += offset;
}
// calculate new intensity levels
byte[] equalizedHistogram = Equalize( histogram, numberOfPixels );
// update pixels' intensities
ptr = (byte*) image.ImageData.ToPointer( );
// allign pointer to the first pixel to process
ptr += ( startY * stride + startX );
for ( int y = startY; y < stopY; y++ )
{
for ( int x = startX; x < stopX; x++, ptr++ )
{
*ptr = equalizedHistogram[*ptr];
}
ptr += offset;
}
}
else
{
// color image
byte* ptr = (byte*) image.ImageData.ToPointer( );
// allign pointer to the first pixel to process
ptr += ( startY * stride + startX * pixelSize );
// calculate histogram
int[] histogramR = new int[256];
int[] histogramG = new int[256];
int[] histogramB = new int[256];
for ( int y = startY; y < stopY; y++ )
{
for ( int x = startX; x < stopX; x++, ptr += pixelSize )
{
histogramR[ptr[RGB.R]]++;
histogramG[ptr[RGB.G]]++;
histogramB[ptr[RGB.B]]++;
}
ptr += offset;
}
// calculate new intensity levels
byte[] equalizedHistogramR = Equalize( histogramR, numberOfPixels );
byte[] equalizedHistogramG = Equalize( histogramG, numberOfPixels );
byte[] equalizedHistogramB = Equalize( histogramB, numberOfPixels );
// update pixels' intensities
ptr = (byte*) image.ImageData.ToPointer( );
// allign pointer to the first pixel to process
ptr += ( startY * stride + startX * pixelSize );
for ( int y = startY; y < stopY; y++ )
{
for ( int x = startX; x < stopX; x++, ptr += pixelSize )
{
ptr[RGB.R] = equalizedHistogramR[ptr[RGB.R]];
ptr[RGB.G] = equalizedHistogramG[ptr[RGB.G]];
ptr[RGB.B] = equalizedHistogramB[ptr[RGB.B]];
}
ptr += offset;
}
}
}
