Error The specified pixel format is not supported. using GifWriter - GifWriter throws error

using (var writer = new GifWriter(gifFlyerPath))

{

writer.FrameOptions.Delay = 200;

for (int i = 0; i < pngFiles.Count; i++)

{

using (var reader = ImageReader.Create(pngFiles[i]))

{

Pipeline.Run(reader + writer);

}

}

}

The png files are created in WPF by rendering a Visual using:

RenderTargetBitmap bmr = new RenderTargetBitmap(

(int) adjustedWidth

, (int) adjustedHeight

, resolut

, resolut

, PixelFormats.Pbgra32);

bmr.Render(ThisDocument.Canvas_Base);

Bitmap bm = null;

using (MemoryStream stream = new MemoryStream())

{

BitmapEncoder encoder = new PngBitmapEncoder();

encoder.Frames.Add(BitmapFrame.Create(bmr));

encoder.Save(stream);

bm = new Bitmap(stream);

var parms = new EncoderParameters(1);

parms.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);

string thisSlidePath = slidePath + sNo + ".png";

bm.Save(thisSlidePath , GetEncoder(ImageFormat.Png), parms);

pngFiles.Add(thisSlidePath);

sNo++;

}