Bitmap Contrast - CSharp System.Drawing

CSharp examples for System.Drawing:Image Operation

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Description

Bitmap Contrast

Demo Code


using System.Drawing.Imaging;
using System.Drawing;
using System;//from  w ww.java  2  s.  co  m

public class Main{
    public static bool Contrast(Bitmap b, sbyte nContrast)
      {
         if (nContrast < -100) return false;
         if (nContrast >  100) return false;

         double pixel = 0, contrast = (100.0+nContrast)/100.0;

         contrast *= contrast;

         int red, green, blue;
         
         // GDI+ still lies to us - the return format is BGR, NOT RGB.
         BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

         int stride = bmData.Stride;
         System.IntPtr Scan0 = bmData.Scan0;

         unsafe
         {
            byte * p = (byte *)(void *)Scan0;

            int nOffset = stride - b.Width*3;

            for(int y=0;y<b.Height;++y)
            {
               for(int x=0; x < b.Width; ++x )
               {
                  blue = p[0];
                  green = p[1];
                  red = p[2];
            
                  pixel = red/255.0;
                  pixel -= 0.5;
                  pixel *= contrast;
                  pixel += 0.5;
                  pixel *= 255;
                  if (pixel < 0) pixel = 0;
                  if (pixel > 255) pixel = 255;
                  p[2] = (byte) pixel;

                  pixel = green/255.0;
                  pixel -= 0.5;
                  pixel *= contrast;
                  pixel += 0.5;
                  pixel *= 255;
                  if (pixel < 0) pixel = 0;
                  if (pixel > 255) pixel = 255;
                  p[1] = (byte) pixel;

                  pixel = blue/255.0;
                  pixel -= 0.5;
                  pixel *= contrast;
                  pixel += 0.5;
                  pixel *= 255;
                  if (pixel < 0) pixel = 0;
                  if (pixel > 255) pixel = 255;
                  p[0] = (byte) pixel;               

                  p += 3;
               }
               p += nOffset;
            }
         }

         b.UnlockBits(bmData);

         return true;
      }
}

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