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

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

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

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

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

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

[c#] Convert an image to grayscale

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