C＃中保存的JPG的质量 [英] Quality of a saved JPG in C#

问题描述

我制作了一个小型C＃应用程序来创建.jpg格式的图像。

I made a small C# app to create an image in .jpg format.

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价。

The image is succesfully created. I input an original pic, do some stuff with it and save it. The quality of this new pic however, is lower than that of the original.

有没有办法设定所需的质量？

Is there any way to set the desired quality?

推荐答案

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。

The following code example demonstrates how to create a EncoderParameter using the EncoderParameter constructor. To run this example, paste the code and call the VaryQualityLevel method.

此示例需要一个名为TestPhoto.jpg的图像文件位于c：。

This example requires an image file named TestPhoto.jpg located at 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

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