Convert an image to grayscale

Question

Is there a way to convert an image to grayscale 16 bits per pixel format  rather than setting each of the r g and b components to luminance  I currently have a bmp from file    Bitmap c   new Bitmap  filename      I want a Bitmap d  that is grayscale version of c  I do see a constructor that includes System Drawing Imaging PixelFormat  but I don t understand how to use that  I m new to Image Processing and the relevant C  libraries  but have a moderate experience with C  itself   Any help  reference to an online source  hint or suggestion will be appreciated    EDIT  d is the grayscale version of c

User · Answer

Bitmap d   new Bitmap c Width  c Height    for  int i   0  i  lt  c Width  i          for  int x   0  x  lt  c Height  x                  Color oc   c GetPixel i  x           int grayScale    int   oc R   0 3     oc G   0 59     oc B   0 11            Color nc   Color FromArgb oc A  grayScale  grayScale  grayScale           d SetPixel i  x  nc             This way it also keeps the alpha channel   Enjoy

User · Answer

There s a static method in ToolStripRenderer class  named CreateDisabledImage  Its usage is as simple as   Bitmap c   new Bitmap  filename    Image d   ToolStripRenderer CreateDisabledImage c     It uses a little bit different matrix than the one in the accepted answer and additionally multiplies it by a transparency of value 0 7  so the effect is slightly different than just grayscale  but if you want to just get your image grayed  it s the simplest and best solution

User · Answer

I want a Bitmap d  that is grayscale    I do see a consructor that includes   System Drawing Imaging PixelFormat    but I don t understand how to use   that       Here is how to do this  Bitmap grayScaleBP   new           System Drawing Bitmap 2  2  System Drawing Imaging PixelFormat Format16bppGrayScale     EDIT  To convert to grayscale               Bitmap c   new Bitmap  fromFile                 Bitmap d               int x  y                   Loop through the images pixels to reset color               for  x   0  x  lt  c Width  x                                    for  y   0  y  lt  c Height  y                                            Color pixelColor   c GetPixel x  y                        Color newColor   Color FromArgb pixelColor R  0  0                        c SetPixel x  y  newColor      Now greyscale                                               d   c       d is grayscale version of c     Faster Version from switchonthecode follow link for full analysis   public static Bitmap MakeGrayscale3 Bitmap original         create a blank bitmap the same size as original    Bitmap newBitmap   new Bitmap original Width  original Height         get a graphics object from the new image    using Graphics g   Graphics FromImage newBitmap              create the grayscale ColorMatrix        ColorMatrix colorMatrix   new ColorMatrix            new float                               new float     3f   3f   3f  0  0                new float     59f   59f   59f  0  0                new float     11f   11f   11f  0  0                new float    0  0  0  1  0                new float    0  0  0  0  1                          create some image attributes        using ImageAttributes attributes   new ImageAttributes                   set the color matrix attribute            attributes SetColorMatrix colorMatrix                 draw the original image on the new image              using the grayscale color matrix            g DrawImage original  new Rectangle 0  0  original Width  original Height                          0  0  original Width  original Height  GraphicsUnit Pixel  attributes                    return newBitmap

User · Answer

The code below is the simplest solution   Bitmap bt   new Bitmap  imageFilePath     for  int y   0  y  lt  bt Height  y          for  int x   0  x  lt  bt Width  x                  Color c   bt GetPixel x  y            int r   c R          int g   c G          int b   c B          int avg    r   g   b    3          bt SetPixel x  y  Color FromArgb avg avg avg                bt Save  d   out bmp

User · Answer

None of the examples above create 8-bit  8bpp  bitmap images   Some software  such as image processing  only supports 8bpp   Unfortunately the MS  NET libraries do not have a solution   The PixelFormat Format8bppIndexed format looks promising but after a lot of attempts I couldn t get it working     To create a true 8-bit bitmap file you need to create the proper headers  Ultimately I found the Grayscale library solution for creating 8-bit bitmap  BMP  files   The code is very simple   Image image   Image FromFile  c  path to image jpg    GrayBMP File CreateGrayBitmapFile image   c  path to 8bpp image bmp      The code for this project is far from pretty but it works  with one little simple-to-fix problem   The author hard-coded the image resolution to 10x10   Image processing programs do not like this   The fix is open GrayBMP File cs  yeah  funky file naming  I know  and replace lines 50 and 51 with the code below   The example sets the resolution to 200x200 but you should change it to the proper number     int resX   200  int resY   200     horizontal resolution Copy to Index DIB header  BitConverter GetBytes resX   100   24      vertical resolution  Copy to Index DIB header  BitConverter GetBytes resY   100   28

User · Answer

To summarize a few items here  There are some pixel-by-pixel options that  while being simple just aren t fast    Luis  comment linking to   archived  https   web archive org web 20110827032809 http   www switchonthecode com tutorials csharp-tutorial-convert-a-color-image-to-grayscale is superb   He runs through three different options and includes timings for each

[c#] Convert an image to grayscale

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