Question

我制作了一个小型C＃应用程序来创建.jpg格式的图像。

pictureBox.Image.Save(name,ImageFormat.Jpeg);

图像已成功创建。我输入原始图片，用它做一些事情并保存。然而，这张新照片的质量低于原始照片的质量。

有没有办法设定所需的质量？

Answer 1

以下代码示例演示如何使用EncoderParameter构造函数创建EncoderParameter。要运行此示例，请粘贴代码并调用VaryQualityLevel方法。

此示例需要名为TestPhoto.jpg的图像文件位于c：。

private void VaryQualityLevel()
{
    // Get a bitmap.
    Bitmap bmp1 = new Bitmap(@"c:\TestPhoto.jpg");
    ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);

    // Create an Encoder object based on the GUID
    // for the Quality parameter category.
    System.Drawing.Imaging.Encoder myEncoder =
        System.Drawing.Imaging.Encoder.Quality;

    // Create an EncoderParameters object.
    // An EncoderParameters object has an array of EncoderParameter
    // objects. In this case, there is only one
    // EncoderParameter object in the array.
    EncoderParameters myEncoderParameters = new EncoderParameters(1);

    EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 
        50L);
    myEncoderParameters.Param[0] = myEncoderParameter;
    bmp1.Save(@"c:\TestPhotoQualityFifty.jpg", jgpEncoder, 
        myEncoderParameters);

    myEncoderParameter = new EncoderParameter(myEncoder, 100L);
    myEncoderParameters.Param[0] = myEncoderParameter;
    bmp1.Save(@"c:\TestPhotoQualityHundred.jpg", jgpEncoder, 
        myEncoderParameters);

    // Save the bitmap as a JPG file with zero quality level compression.
    myEncoderParameter = new EncoderParameter(myEncoder, 0L);
    myEncoderParameters.Param[0] = myEncoderParameter;
    bmp1.Save(@"c:\TestPhotoQualityZero.jpg", jgpEncoder, 
        myEncoderParameters);

}

private ImageCodecInfo GetEncoder(ImageFormat format)
{
    ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
    foreach (ImageCodecInfo codec in codecs)
    {
        if (codec.FormatID == format.Guid)
        {
            return codec;
        }
    }
    return null;
}

参考：http://msdn.microsoft.com/en-us/library/system.drawing.imaging.encoderparameter.aspx

Answer 2

这里有一个更紧凑的代码块，用于保存具有特定质量的JPEG：

var encoder = ImageCodecInfo.GetImageEncoders().First(c => c.FormatID == ImageFormat.Jpeg.Guid);
var encParams = new EncoderParameters() { Param = new[] { new EncoderParameter(Encoder.Quality, 90L) } };
image.Save(path, encoder, encParams);

或者，如果120个字符宽的行太长了你：

var encoder = ImageCodecInfo.GetImageEncoders()
                            .First(c => c.FormatID == ImageFormat.Jpeg.Guid);
var encParams = new EncoderParameters(1);
encParams.Param[0] = new EncoderParameter(Encoder.Quality, 90L);
image.Save(path, encoder, encParams);

确保质量为long，否则您将获得ArgumentException！

Answer 3

这是一个旧线程，但我重写了微软（根据Dustin Getz的回答）更有用 - 缩小GetEncoderInfo并在Image上进行扩展。无论如何没有什么新东西，但可能有用：

    /// <summary>
    /// Retrieves the Encoder Information for a given MimeType
    /// </summary>
    /// <param name="mimeType">String: Mimetype</param>
    /// <returns>ImageCodecInfo: Mime info or null if not found</returns>
    private static ImageCodecInfo GetEncoderInfo(String mimeType)
    {
        var encoders = ImageCodecInfo.GetImageEncoders();
        return encoders.FirstOrDefault( t => t.MimeType == mimeType );
    }

    /// <summary>
    /// Save an Image as a JPeg with a given compression
    ///  Note: Filename suffix will not affect mime type which will be Jpeg.
    /// </summary>
    /// <param name="image">Image: Image to save</param>
    /// <param name="fileName">String: File name to save the image as. Note: suffix will not affect mime type which will be Jpeg.</param>
    /// <param name="compression">Long: Value between 0 and 100.</param>
    private static void SaveJpegWithCompressionSetting(Image image, string fileName, long compression)
    {
        var eps = new EncoderParameters(1);
        eps.Param[0] = new EncoderParameter(Encoder.Quality, compression);
        var ici = GetEncoderInfo("image/jpeg");
        image.Save(fileName, ici, eps);
    }

    /// <summary>
    /// Save an Image as a JPeg with a given compression
    /// Note: Filename suffix will not affect mime type which will be Jpeg.
    /// </summary>
    /// <param name="image">Image: This image</param>
    /// <param name="fileName">String: File name to save the image as. Note: suffix will not affect mime type which will be Jpeg.</param>
    /// <param name="compression">Long: Value between 0 and 100.</param>
    public static void SaveJpegWithCompression(this Image image, string fileName, long compression)
    {
        SaveJpegWithCompressionSetting( image, fileName, compression );
    }

Answer 4

使用无类型GDI +样式（https://msdn.microsoft.com/en-us/library/windows/desktop/ms533845(v=vs.85).aspx）属性来设置JPEG质量看起来过于苛刻。

直接的方式应如下所示：

FileStream stream = new FileStream("new.jpg", FileMode.Create);
JpegBitmapEncoder encoder = new JpegBitmapEncoder();
encoder.QualityLevel = 100;   // "100" for maximum quality (largest file size).
encoder.Frames.Add(BitmapFrame.Create(image));
encoder.Save(stream);

参考：https://msdn.microsoft.com/en-us/library/system.windows.media.imaging.jpegbitmapencoder.rotation(v=vs.110).aspx#Anchor_2

Answer 5

查看MSDN上有关how to set JPEG Compression level的文章。

您需要使用另一个带有ImageEncoder及其参数的Save（）重载。

Answer 6

社区维基的答案被接受，引用了微软的一个例子。

然而，为了节省你们的一些时间，我把它归结为一个本质和

将其打包成适当的方法
已实施IDisposable。在任何其他答案中我都没有看到using (...) {。为了避免内存泄漏，最好先处理实现IDisposable。

public static void SaveJpeg(string path, Bitmap image)
{
    SaveJpeg(path, image, 95L);
}
public static void SaveJpeg(string path, Bitmap image, long quality)
{
    using (EncoderParameters encoderParameters = new EncoderParameters(1))
    using (EncoderParameter encoderParameter = new EncoderParameter(Encoder.Quality, quality))
    {
        ImageCodecInfo codecInfo = ImageCodecInfo.GetImageDecoders().First(codec => codec.FormatID == ImageFormat.Jpeg.Guid);
        encoderParameters.Param[0] = encoderParameter;
        image.Save(path, codecInfo, encoderParameters);
    }
}

Answer 7

如果您使用的是.NET Compact Framework，另一种方法可能是使用PNG无损格式，即：

image.Save(filename, ImageFormat.Png);

C＃中保存的JPG的质量

7 个答案: