index > Windows Forms General > ImageList increasing color depth.

ImageList increasing color depth.

            ImageList imageList1 = new ImageList();
            imageList1.ColorDepth = ColorDepth.Depth8Bit;
            Bitmap bitmap1 = new Bitmap(16, 16, PixelFormat.Format8bppIndexed);
            imageList1.Images.Add(bitmap1);
            PixelFormat pixelFormat1 = bitmap1.PixelFormat; //Format8bppIndexed
            PixelFormat pixelFormat2 = imageList1.Images[0].PixelFormat; //Format32bppArgb

Why is a 32bpp copy of the bitmap being made when I add to the ImageList? How can I make the ImageList use 8bpp images? This would greatly reduce the memory usage of my application, as it requires thousands of images in the ImageList of a ListView.

Thank you!

Gannon_____ Friday, October 02, 2009 1:22 PM

When you use the ImageList.Image[] getter, it creates a new bitmap from the image stored in the image list. That new bitmap has the system default image format. You must Dispose() it.

Hans Passant.

Marked As Answer byGannon_____ Friday, October 02, 2009 6:51 PM

nobugz Friday, October 02, 2009 3:44 PM

When you use the ImageList.Image[] getter, it creates a new bitmap from the image stored in the image list. That new bitmap has the system default image format. You must Dispose() it.

Hans Passant.

Marked As Answer byGannon_____ Friday, October 02, 2009 6:51 PM

nobugz Friday, October 02, 2009 3:44 PM

OK so are you implying that the above call to Add results in an 8bpp bitmap being added, and a 32bpp one only exists after the the call to Images[] ? I'm not really sure... Thanks.

Gannon_____ Friday, October 02, 2009 5:35 PM

Yes. An 8bpp ImageList cannot store a 32bpp bitmap. If you are running low on memory, make sure that you are disposing bitmaps properly.

Hans Passant.

nobugz Friday, October 02, 2009 6:19 PM

Well that was dumb, but now I know. Yeah, the ImageList uses the same amount of memory as a a List<Image>. Now I wonder how the behavior of ImageList.Image[] would be considered correct or desirable by anyone. That's like, a bug, or something.

Gannon_____ Friday, October 02, 2009 7:17 PM

It is desirable, GDI+ has very poor support for indexed pixel formats. You can load and save them, that's all. Drawing is not possible.

Hans Passant.

nobugz Friday, October 02, 2009 7:49 PM

You can use google to search for other answers

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