Why does resizing a png image lose transparency?

c#, image, png, resize, transparency

Solution

Your code doesn't do quite what you think that it does...

You use the GetThumbnailImage to resize the image, then you draw the thumbnail image into itself which is rather pointless. You probably lose the transparency in the first step.

Create a blank bitmap instead, and resize the source image by drawing it on the blank bitmap.

private byte[] GetThumbNail(string imageFile) {
  try {
    byte[] result;
    using (Image thumbnail = new Bitmap(160, 59)) {
      using (Bitmap source = new Bitmap(imageFile)) {
        using (Graphics g = Graphics.FromImage(thumbnail)) {
          g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
          g.InterpolationMode =  System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
          g.DrawImage(source, 0, 0, 160, 59);
        }
      }
      using (MemoryStream ms = new MemoryStream()) {
        thumbnail.Save(ms, ImageFormat.Png);
        thumbnail.Save("test.png", ImageFormat.Png);
        result = ms.ToArray();
      }
    }
    return result;
  } catch (Exception) {
    throw;
  }
}

(I removed some parameters that were never used for anything that had anything to do with the result, like the imageLen parameter that was only used to create a byte array that was never used.)

Problem

Original source