Bitmap.Clone() doesn't always honor requested PixelFormat and thus results in Stackoverflow in Encode() recursion.

[crokusek]

Hi there!

Fyi, the following method generates a stackoverflow exception here due to recursion with certain PixcelFormats:

Inside SimpleEncoder.cs...

public void Encode(Bitmap b, float quality, out IntPtr result, out long length)
{
if (b.PixelFormat == PixelFormat.Format32bppArgb)
{
...convert...
}
else if (b.PixelFormat == PixelFormat.Format24bppRgb)
{
...convert...
}
else
{
// The problem occurs here with some input PixelFormat types.
// Notably PixelFormat = 8207 (undocumented non-enum value) occurs from streaming in a CMYK jpg
// https://stackoverflow.com/questions/5065371
// The bitmap.Clone() result below does not honor the requested the pixel format and
// returning the same PixelFormat type and so the recursive call ends up in this
// same block until a stackoverflow exception.

    // From this other related issue, there are other types then PixelFormat 8207 where 
    // this happens:  https://stackoverflow.com/questions/2016406
    //
    // To resolve, suggest using an GDI approach like the first answer here which 
    // uses Graphics to write into a new bitmap() for all pixelformats instead of Clone().
    // https://stackoverflow.com/a/2016509/538763        
    // I have verified the answer to work against 8207 (outside of the library code).

using Bitmap b2 = b.Clone(new Rectangle(0, 0, b.Width, b.Height), PixelFormat.Format32bppArgb);
Encode(b2, quality, out result, out length);    // RECURSE

}

And thanks for the library!