convert 32bpp Bitmap to 16bpp (Grayscale)

Question

I'm creating a Bitmap in C# from an Image object.

The Bitmap I get is 32bpp, how can I transform that to 16bpp?

Bitmap image_bmp;
System.Drawing.Image tmp = (System.Drawing.Image)img.RenderImage(0); //RenderImage creates an object of tyoe System.Drawing.Image
image_bmp = new Bitmap(tmp);

Answer 1

If you run a quick search on google you can find a number of excellent color to grayscale formulas. Take the following from wikipedia as an example:

Y' =  0.2126 R' + 0.7152 G' + 0.0722 B'

With this in mind the general process in .NET is going to be:

• Create a new image of the correct dimensions with 16bpp grayscale
• Use "LockBits" on the original image and the new image and loop over each pixel
• Unlock both images, then save the new image to a file

Rather than going into these steps further I found a few other questions from stack and around the web that really delve into the details more. See:

• Set individual pixels in .NET Format16bppGrayScale image
• How to convert pixel formats? From 32bppRGB to 16bpp grayscale in C#
• http://social.msdn.microsoft.com/Forums/vstudio/en-US/10252c05-c4b6-49dc-b2a3-4c1396e2c3ab/writing-a-16bit-grayscale-image?forum=csharpgeneral

Best of luck!

NOTE - I'm assuming your using GDI+. The steps are is similar for Windows Imaging Component (WIC) but the classes and syntax is radically different.