C# bitmap图片编码及压缩参数

读取图片

Image img = Image.FromFile(imgFile);

ImageCodecInfo 帮助方法

简写：

private static ImageCodecInfo GetEncoder(ImageFormat format)
{
    var codecs = ImageCodecInfo.GetImageDecoders();
    return codecs.FirstOrDefault(codec => codec.FormatID == format.Guid);
}

原始

private ImageCodecInfo GetEncoder(ImageFormat format)
{
    ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

    foreach (ImageCodecInfo codec in codecs)
    {
        if (codec.FormatID == format.Guid)
        {
            return codec;
        }
    }
    return null;
}

编码及压缩

Bitmap target = new Bitmap(width, height);

// format and encoder
// the format is used by the encoder
// to generate ImageCodecInfo
ImageFormat format = ImageFormat.Jpeg;
ImageCodecInfo encoder = GetEncoder(format);

// Bitmap.Save takes the EncoderParameters,
// but what we make is a EncoderParameter, no "s" at the end.
// use EncoderParameters.Param[0] to assign
EncoderParameters pm = new EncoderParameters(1);
pm.Param[0] = new EncoderParameter(Encoder.Quality, 80L);

string filename = ...
target.Save(filename, encoder, pm);

附：裁剪图片

Rectangle cropRect = new Rectangle(x, y, width, height);

Bitmap target = new Bitmap(width, height);
Graphics g = Graphics.FromImage(target);
g.DrawImage(img, 
            new Rectangle(0, 0, target.Width, target.Height),
            cropRect,
            GraphicsUnit.Pixel);