Compress animated gif image size using c#

Question

I wanted to create animated gif image from several images using c#, so i have used below github solution to do so.

https://github.com/DataDink/Bumpkit

I am using below code to do it

using (var gif = File.OpenWrite(@"C:\IMG_TEST.gif"))
using (var encoder = new GifEncoder(gif))
    for (int i = 0, count = imageFilePaths.Length; i < count; i++)
    {
        Image image = Image.FromFile(imageFilePaths[i]);
        encoder.AddFrame(image,0,0);
    }

it is working like a charm, but it is creating gif of size 45 MB. If i check my actual image size , then it is only 11MB with total 47 images. but somehow gif is generating with big size.

Now i want to compress the size of gif image which is being created using c#.

So is there any way i can compress the size of gif image?

Answer 1

I know this is an old question, but figured I'd share this solution.

I ran into the same issue and found that each frame should contain only the differences in pixels from the previous frame. I thought that the encoder would do the image diff for me, but apparently it doesn't.

So before adding each frame, I compare it to the previous frame using this method I wrote. I then add the resulting image that contains only the changed pixels.

Here's where I'm using it: https://github.com/Jay-Rad/CleanShot/blob/master/CleanShot/Classes/GIFRecorder.cs

public class ImageDiff
{
    public static Bitmap GetDifference(Bitmap bitmap1, Bitmap bitmap2)
    {
        if (bitmap1.Height != bitmap2.Height || bitmap1.Width != bitmap2.Width)
        {
            throw new Exception("Bitmaps are not of equal dimensions.");
        }
        if (!Bitmap.IsAlphaPixelFormat(bitmap1.PixelFormat) || !Bitmap.IsAlphaPixelFormat(bitmap2.PixelFormat) ||
            !Bitmap.IsCanonicalPixelFormat(bitmap1.PixelFormat) || !Bitmap.IsCanonicalPixelFormat(bitmap2.PixelFormat))
        {
            throw new Exception("Bitmaps must be 32 bits per pixel and contain alpha channel.");
        }
        var newImage = new Bitmap(bitmap1.Width, bitmap1.Height);

        var bd1 = bitmap1.LockBits(new System.Drawing.Rectangle(0, 0, bitmap1.Width, bitmap1.Height), ImageLockMode.ReadOnly, bitmap1.PixelFormat);
        var bd2 = bitmap2.LockBits(new System.Drawing.Rectangle(0, 0, bitmap2.Width, bitmap2.Height), ImageLockMode.ReadOnly, bitmap2.PixelFormat);
        // Get the address of the first line.
        IntPtr ptr1 = bd1.Scan0;
        IntPtr ptr2 = bd2.Scan0;

        // Declare an array to hold the bytes of the bitmap.
        int bytes = Math.Abs(bd1.Stride) * bitmap1.Height;
        byte[] rgbValues1 = new byte[bytes];
        byte[] rgbValues2 = new byte[bytes];

        // Copy the RGBA values into the array.
        Marshal.Copy(ptr1, rgbValues1, 0, bytes);
        Marshal.Copy(ptr2, rgbValues2, 0, bytes);

        // Check RGBA value for each pixel.
        for (int counter = 0; counter < rgbValues1.Length - 4; counter += 4)
        {
            if (rgbValues1[counter] != rgbValues2[counter] ||
                rgbValues1[counter + 1] != rgbValues2[counter + 1] ||
                rgbValues1[counter + 2] != rgbValues2[counter + 2] ||
                rgbValues1[counter + 3] != rgbValues2[counter + 3])
            {
                // Change was found.
                var pixel = counter / 4;
                var row = (int)Math.Floor((double)pixel / bd1.Width);
                var column = pixel % bd1.Width;
                newImage.SetPixel(column, row, Color.FromArgb(rgbValues1[counter + 3], rgbValues1[counter + 2], rgbValues1[counter + 1], rgbValues1[counter]));
            }
        }
        bitmap1.UnlockBits(bd1);
        bitmap2.UnlockBits(bd2);
        return newImage;
    }
}