Using GDI+ to make 'PNG with added CMYK'?

I want to create a PNG file from a System.Drawing.Bitmap with the colours defined using CMYK.

I can create the PNG OK but how do I define 'with CMYK' ?

I've looked at the encoderparameters argument to the s开发者_运维技巧ave method but it seems to me they don't cover what I need ?

Any pointers/samples appreciated.

thanks

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The PNG format was designed for transferring graphics for display on computer screens. PNG files may only transfer grayscale or RGB/RGBA image data; you can't have a CMYK PNG file: http://www.w3.org/TR/2003/REC-PNG-20031110/#11IHDR

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        MemoryStream ms=new MemoryStream();
        ImageCodecInfo imageCodecInfo = ImageCodecInfo.GetImageDecoders()[0];
        EncoderParameters encoderParameters=new EncoderParameters(1);
        encoderParameters.Param[0] = new EncoderParameter(Encoder.Compression,(int)EncoderValue.);
        bmp.Save(ms,imageCodecInfo, encoderParameters);
        Bitmap newbmp = (Bitmap) Image.FromStream(ms);
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