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Dithered Gif images created by .Net

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Last Modified: 2013-12-16
I am dynamically creating images in .Net 3.0, but each format is giving me problems.
- When I save as Gif, the image is (I think the term is) 'ditherered'
- When I save as Png, it looks great in Firefox but in IE7 the colours ae not correct (for example in IE7 renders #CD5C5C as #C75151 - compare attached file in FF and IE).

So I either need the gif to be non-dithered, or the Png to work in IE - ideally a solution for both would be great.
Thanks
// Creates a square with a circle in the middle.
Bitmap tn = new Bitmap(30, 30);
Graphics gForm = Graphics.FromImage(tn);
 
gForm.CompositingMode = CompositingMode.SourceOver;
gForm.CompositingQuality = CompositingQuality.HighQuality;
gForm.SmoothingMode = SmoothingMode.HighQuality; ;
 
// Draw the background.
Brush BackBrush = new SolidBrush(Color.IndianRed);
gForm.FillRectangle(BackBrush, 0, 0, tn.Height, tn.Width);
BackBrush.Dispose();
 
Brush FillBrush = new SolidBrush(Color.BlueViolet);
gForm.FillEllipse(FillBrush, 10, 10, 10, 10);
FillBrush.Dispose();
 
tn.Save(OutputFolder + @"test.jpg", ImageFormat.Jpeg); //too blury!
tn.Save(OutputFolder + @"test.Gif", ImageFormat.Gif); // too dithered!
tn.Save(OutputFolder + @"test.Png", ImageFormat.Png); // IE7 problem!

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test.Gif
test.Png
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