1. Brightness - Introduction
2. Brightness - The Algorithm
3. Contrast - Introduction
4. Contrast - The Algorithm

Comments

1. Mitch Dusina
   11 Sep 2007 at 04:55

   I have just returned from an extended absence from this forum so I realize this is rather late.
   
   JohnMAndre:
   1) I'm not sure how that even got in there, I'll remove it at once.
   2) I was almost certain I had inclueded the code for the SupportFunctions, my mistake.  I'll correct it in the article
   
   MD2020:
   GetPixel/SetPixel is the slowest way of doing image processing in .NET, not using unsafe code.  The unsafe method is quiet fast actually.  As for using a ColorMatrix, it is fast as well.  However at the time of writing this article my research showed that a ColorMatrix was slightly slower than unsafe code (noticable on large images or slow machines).  However as of this posting, I have found mixed arguments.  Either way, they have similar speeds.  I'll try to run some benchmarks to verify the correct answer (or if someone would like to do it and post their results here).
   
   
   
   
   
   
   
   
   

2. Atandriya Kumar Sahoo
   05 Jun 2007 at 13:25

   Hi

   I think this is code for brightness only... wat will be the contrast code...

   Thanks.

   Atan Kumar

3. siddharth.sid
   30 Nov 2006 at 18:15

   hey I am not able to decrease brightness though I can increase it
   
   

4. Trey Adams
   11 Sep 2006 at 22:13

   Locking the image and using an unsafe block is the slowest way to do image processing in GDI+. There is an even faster way to do this. Use a color Matrix. Here is the code.

    

   public static void AdjustBrightnessMatrix(Bitmap img, int value)

           {

               if (value == 0) // No change, so just return

                   return;

    

               float sb = (float)value / 255F;

               float[][] colorMatrixElements =

                     {

                           new float[] {1,  0,  0,  0, 0},

                           new float[] {0,  1,  0,  0, 0},

                           new float[] {0,  0,  1,  0, 0},

                           new float[] {0,  0,  0,  1, 0},

                           new float[] {sb, sb, sb, 1, 1}

                     };

    

               ColorMatrix cm = new ColorMatrix(colorMatrixElements);

               ImageAttributes imgattr = new ImageAttributes();

               Rectangle rc = new Rectangle(0, 0, img.Width, img.Height);

               Graphics g = Graphics.FromImage(img);

               g.InterpolationMode = InterpolationMode.HighQualityBicubic;

               imgattr.SetColorMatrix(cm);

               g.DrawImage(img, rc, 0, 0, img.Width, img.Height, GraphicsUnit.Pixel, imgattr);

              

               //Clean everything up

               imgattr.Dispose();

               g.Dispose();

           }

5. John M. Andre
   30 Aug 2006 at 09:12

   A fine article, but there are two small points you might want to address:
   
   1) The code is in C# but there is a VB line-continuation character. Unless you remove it, the code will not compile.
   
   2) You call SupportFunctions.BytesPerPixel but you don't list the code for that. Therefore, the code will still not compile.
   
   Of course, the reader can always research these problems and find solutions but it would be nice to have all the answers in one place.
   
   Best Regards,
   John
   
   
   
   
   
   
   
   
   
   
   
   
   

6. Developer Fusion Bot
   01 Jan 1999 at 00:00

   This thread is for discussions of Image Manipulation - Brightness and Contrast.