在C＃中将位图从16bpp转换为8bpp

Question

I have a Bitmap with 16bpp. I want to convert that image in my ASP.NET side in a 8bpp image.

I tried a lot of options which I found in the internet but nothing works for me.

I also tried that way: C# Converting 32bpp image to 8bpp

But if I want to save the file, I get the following error:

Exception Details: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+.

Line 278:                    System.Drawing.Image img2 = Convert(bm_resize);//byteArrayToImage(gray);
Line 279:                    
Line 280:                    img2.Save(helper+"grey2.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
Line 281:                }
Line 282:

Is there any correct way for my problem?

Full Code:

System.Drawing.Image img2 = Convert(bm_resize);
img2.Save(path+"test.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);


public static System.Drawing.Image Convert(Bitmap oldbmp)
    {
        using (MemoryStream ms = new MemoryStream())
        {
            oldbmp.Save(ms, ImageFormat.Gif);
            ms.Position = 0;
            return System.Drawing.Image.FromStream(ms);
        }
    }

Answer 1

The problem is caused by disposing the memory stream before the image is saved.

I believe GDI+ requires the memory stream to persist while you are still working with an Image created from the memory stream.

See the Microsoft Support article.

Answer 2

I use a little helper function to create 1 bpp monochrome bitmaps in .NET. Check out this link, it also works great for 8 bpp

http://www.wischik.com/lu/programmer/1bpp.html

hope this could help!

Answer 3

AForge.Net has a good collection of free (under Lesser GPL License) routines for such changes and a lot more. Conversion of 16bpp to 8bpp is as simple as this .