C#缩减图片文件大小

    private void button1_Click(object sender, EventArgs e)
    {
        Image myImage = Image.FromFile(@"D:\pic\original.jpg", true);
        SaveImg(@"D:\pic\reduced.jpg", myImage, 50);
    }

    public static void SaveImg(string path, Image img, int quality)
    {
        if (quality < 0 || quality > 100)
            throw new ArgumentOutOfRangeException("quality must be between 0 and 100.");

        // Encoder parameter for image quality 
        EncoderParameter qualityParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
        // JPEG image codec 
        ImageCodecInfo jpegCodec = GetEncoderInfo("image/jpeg");
        EncoderParameters encoderParams = new EncoderParameters(1);
        encoderParams.Param[0] = qualityParam;
        img.Save(path, jpegCodec, encoderParams);
        img.Dispose();
    }

    private static ImageCodecInfo GetEncoderInfo(string mimeType)
    {
        // Get image codecs for all image formats 
        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

        // Find the correct image codec 
        for (int i = 0; i < codecs.Length; i++)
            if (codecs[i].MimeType == mimeType)
                return codecs[i];

        return null;
    }

测试结果：

https://stackoverflow.com/questions/1922040/how-to-resize-an-image-c-sharp/24199315#24199315