I have a piece of code which resizes animated gifs. if it helps the code will always resize images to a smaller size. (there's no need to make them bigger for now)
I am using Atalasoft's dotimage library and their example code to do the actual resampling. The code is supposed to read an animated gif from disk, iterate through the frames and resize each frame to the new size. This works fine when the gif animation contains frames of the same size but resizing a animation with different sized frames breaks the animation (the frames don't overlap each other correctly after resizing), I think it's because the code is not computing the new offsets correctly.
I think it's this line of code which is not computing the offsets right: Point point = new Point((int)(frame.Location.X * ratio), (int)(frame.Location.Y * ratio));
Here's the complete resize routine:
static private void GenerateGifImage(FileStream fileStream, int OutputWidth, int OutputHeight)
{
// MemoryStream InputStream = new MemoryStream();
FileStream InputStream = fileStream;
// fileStream.Write(InputStream.GetBuffer(), 0, (int)InputStream.Position);
// InputStream.Seek(0, SeekOrigin.Begin);
Image InputImage = Image.FromStream(InputStream, true, false);
// this will invalidate the underlying image object in InputImage but the class properties
// will still accessible until the object is disposed
InputStream.Seek(0, SeekOrigin.Begin);
ImageInfo imageInfo = RegisteredDecoders.GetImageInfo(InputStream);
InputStream.Seek(0, SeekOrigin.Begin);
GifDecoder gifDecoder = new GifDecoder();
int count = gifDecoder.GetFrameCount(InputStream);
GifFrameCollection gifFrameCollection = new GifFrameCollection();
gifFrameCollection.Height = OutputHeight;
gifFrameCollection.Width = OutputWidth;
// gifFrameCollection.Height = gifDecoder.Frames.Height;
// gifFrameCollection.Width = gifDecoder.Frames.Width;
double ratio;
if (InputImage.Height > InputImage.Width)
{
ratio = (double)OutputHeight / (double)InputImage.Height;
}
else
{
ratio = (double)OutputWidth / (double)InputImage.Width;
}
for (int i = 0; i < count; i++)
{
GifFrame frame = gifDecoder.Frames[i];
Rectangle rectangle = new Rectangle(Point.Empty, frame.Image.Size);
int frameWidth = (int)(frame.Image.Width * ratio);
int frameHeight = (int)(frame.Image.Height * ratio);
// account for erratic rounding, seems illogical but has happened earlier when using floats instead of doubles
if (frameWidth > OutputWidth)
{
frameWidth = OutputWidth;
}
if (frameHeight > OutputHeight)
{
frameHeight = OutputHeight;
}
Size size = new Size(frameWidth, frameHeight);
// only resize if we have a measureable dimension
if (size.Width > 0 && size.Height > 0)
{
// ResampleCommand resampleCommand = new ResampleCommand(rectangle, size, ResampleMethod.NearestNeighbor);
ResampleCommand resampleCommand = new ResampleCommand(rectangle, size, ResampleMethod.NearestNeighbor);
AtalaImage atalaImage = resampleCommand.Apply(frame.Image).Image;
// save the image for debugging
// atalaImage.Save("frame" + i.ToString() + ".gif", ImageType.Gif, null);
// frame.Image.Save("frame-orig" + i.ToString() + ".gif", ImageType.Gif, null);
// AtalaImage atalaImage = frame.Image;
Point point = new Point((int)(frame.Location.X * ratio), (int)(frame.Location.Y * ratio));
// Point point = new Point((int)(frame.Location.X), (int)(frame.Location.Y));
gifFrameCollection.Add(new GifFrame(atalaImage, point, frame.DelayTime, frame.Interlaced, frame.FrameDisposal, frame.TransparentIndex, frame.UseLocalPalette));
}
}
FileStream saveStream = new FileStream("resized.gif", FileMode.Create, FileAccess.Write, FileShare.Write);
GifEncoder gifSave = new GifEncoder();
gifSave.Save(saveStream, gifFrameCollection, null);
saveStream.Close();
}
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