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POUnexpected "Bitmap Region is already Locked" exception with GetEncoderParameterList. Any ideas?
 

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  1. POUnexpected "Bitmap Region is already Locked" exception with GetEncoderParameterList. Any ideas?
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    <p>I'm trying to use this sample code from Microsoft to determine what encoder options are available for the JPEG encoder. (The real problem I'm trying to solve is to see if I can set the Chroma subsampling parameters explicitly)</p> <p><a href="http://msdn.microsoft.com/en-us/library/bb882589.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/bb882589.aspx</a></p> <pre><code>private void GetSupportedParameters(PaintEventArgs e) { Bitmap bitmap1 = new Bitmap(1, 1); ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg); EncoderParameters paramList = bitmap1.GetEncoderParameterList(jpgEncoder.Clsid); EncoderParameter[] encParams = paramList.Param; StringBuilder paramInfo = new StringBuilder(); for (int i = 0; i &lt; encParams.Length; i++) { paramInfo.Append("Param " + i + " holds " + encParams[i].NumberOfValues + " items of type " + encParams[i].ValueType + "\r\n" + "Guid category: " + encParams[i].Encoder.Guid + "\r\n"); } e.Graphics.DrawString(paramInfo.ToString(), this.Font, Brushes.Red, 10.0F, 10.0F); } private ImageCodecInfo GetEncoder(ImageFormat format) { ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders(); foreach (ImageCodecInfo codec in codecs) { if (codec.FormatID == format.Guid) { return codec; } } return null; } </code></pre> <p>The problem is, "GetEncoderParameterList" always throws an exception: Bitmap Region Is already Locked.</p> <p>I tried putting the code at the very beginning of my program, and not in an on-paint event handler. Same thing. I tried changing the bit depth on the bitmap, and creating bitmaps in other ways, no difference.</p> <p>Any idea why .NET would think a freshly created bitmap has a locked region?</p> <hr> <p>Update! Some more info: If I use a TIFF encoder, it doesn't fail:</p> <pre><code> Bitmap bitmap1 = new Bitmap(1, 1); ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.TIFF); // TIFF instead of JPEG EncoderParameters paramList = bitmap1.GetEncoderParameterList(jpgEncoder.Clsid); EncoderParameter[] encParams = paramList.Param; </code></pre> <p>So I think this may just be a bug/limitation of GetEncoderparameterList for jpeg....</p>
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