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I am reducing image size to 8*8 to compute average hash to find similar images using C#. I am planning to use Lanczos algorithm to reduce the image size, as it seems to give good results (read from the internet and also python image hashing algo uses the same). Could you point me to where I can find the Lanczos algorithm, implemented in C#? Else is there any better way to do than Lanczos. Please help here.

Thanks

Hemanath
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2 Answers2

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No idea about the algorithm, but the way to resize an image is fairly easy:

    public static Bitmap ResizeImage(Image image, Int32 width, Int32 height)
    {
        Bitmap destImage = new Bitmap(width, height);
        using (Graphics graphics = Graphics.FromImage(destImage))
            graphics.DrawImage(image, new Rectangle(0, 0, width, height), 0, 0, image.Width, image.Height, GraphicsUnit.Pixel);
        return destImage;
    }

With this, you can load the original image, resize it, and save the resized image to disk:

public void ResizeImageFromPath(String imagePath, Int32 width, Int32 height, String savePath)
{
    if (savePath == null)
        savePath = imagePath;
    Byte[] bytes = File.ReadAllBytes(imagePath);
    using (MemoryStream stream = new MemoryStream(bytes))
    using (Bitmap image = new Bitmap(stream))
    using (Bitmap resized = ResizeImage(image, newwidth, newheight))
        resized.Save(savePath, ImageFormat.Png);
}
Nyerguds
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   using (Bitmap bitmap = (Bitmap)Image.FromFile("file.jpg"))
    {
        using (Bitmap newBitmap = new Bitmap(bitmap))
        {
            newBitmap.SetResolution(8, 8);
            newBitmap.Save("file_64.jpg", ImageFormat.Jpeg);
        }
    }

You can change the ImageFormat in the Save-Function to get another compression-rate.