c#将图片格式转换为jpg

c# convert image formats to jpg

提问by mashta gidi

I need to get a picture from the user, with different format extensions, and I want to always save it as "jpg", for easy handling. is there a good way do that in c# without arming the quality?

我需要从用户那里获取具有不同格式扩展名的图片，并且我希望始终将其保存为“jpg”，以便于处理。在不保证质量的情况下，在 C# 中是否有一个好方法？

采纳答案by 465544

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

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

private void VaryQualityLevel()
{
// Get a bitmap.
Bitmap bmp1 = new Bitmap(@"c:\TestPhoto.jpg");
ImageCodecInfo jpgEncoder = 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", jpgEncoder, 
    myEncoderParameters);

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

}

...

private ImageCodecInfo GetEncoder(ImageFormat format)
{

    ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

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

回答by Slavo

You can use the Image APIs to create an image in-memory, and then persist it in JPG. http://msdn.microsoft.com/en-us/library/ms142147.aspx

您可以使用图像 API 在内存中创建图像，然后将其保存在 JPG 中。 http://msdn.microsoft.com/en-us/library/ms142147.aspx

回答by Niranjan Singh

Windows GDI+ provides the Image classand the Bitmap classfor storing images in memory and manipulating images in memory. GDI+ writes images to disk files with the help of image encoders and loads images from disk files with the help of image decoders.

Windows GDI+ 提供了Image 类和Bitmap 类，用于在内存中存储图像和在内存中操作图像。GDI+ 在图像编码器的帮助下将图像写入磁盘文件，并在图像解码器的帮助下从磁盘文件加载图像。

Check Image.Save Methodoverloads to implement your functionality. which support various image format of type ImageFormat Class.

检查Image.Save 方法重载以实现您的功能。它支持ImageFormat Class类型的各种图像格式。

follow example on Image.Save Method (String, ImageCodecInfo, EncoderParameters), which will let you save Jpgfile with encoding etc.

按照Image.Save Method (String, ImageCodecInfo, EncoderParameters)上的示例，它可以让您Jpg使用编码等保存文件。

code snippet:

代码片段：

using System;
using System.Drawing;
using System.Drawing.Imaging;
class Example_SetJPEGQuality
{
    public static void Main()
    {
        Bitmap myBitmap;
        ImageCodecInfo myImageCodecInfo;
        Encoder myEncoder;
        EncoderParameter myEncoderParameter;
        EncoderParameters myEncoderParameters;

        // Create a Bitmap object based on a BMP file.
        myBitmap = new Bitmap("Shapes.bmp");

        // Get an ImageCodecInfo object that represents the JPEG codec.
        myImageCodecInfo = GetEncoderInfo("image/jpeg");

        // Create an Encoder object based on the GUID

        // for the Quality parameter category.
        myEncoder = 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.
        myEncoderParameters = new EncoderParameters(1);

        // Save the bitmap as a JPEG file with quality level 25.
        myEncoderParameter = new EncoderParameter(myEncoder, 25L);
        myEncoderParameters.Param[0] = myEncoderParameter;
        myBitmap.Save("Shapes025.jpg", myImageCodecInfo, myEncoderParameters);

        // Save the bitmap as a JPEG file with quality level 50.
        myEncoderParameter = new EncoderParameter(myEncoder, 50L);
        myEncoderParameters.Param[0] = myEncoderParameter;
        myBitmap.Save("Shapes050.jpg", myImageCodecInfo, myEncoderParameters);

        // Save the bitmap as a JPEG file with quality level 75.
        myEncoderParameter = new EncoderParameter(myEncoder, 75L);
        myEncoderParameters.Param[0] = myEncoderParameter;
        myBitmap.Save("Shapes075.jpg", myImageCodecInfo, myEncoderParameters);
    }

// Codec info

// 编解码器信息

  private static ImageCodecInfo GetEncoderInfo(String mimeType)
        {
            int j;
            ImageCodecInfo[] encoders;
            encoders = ImageCodecInfo.GetImageEncoders();
            for(j = 0; j < encoders.Length; ++j)
            {
                if(encoders[j].MimeType == mimeType)
                    return encoders[j];
            }
            return null;
        }

    }

Hope this help..

希望这有帮助..

回答by Sam Jones

I use this simple extension to convert a stream, all it does is convert it though and does nothing for quality.

我使用这个简单的扩展来转换流，它所做的只是转换它并且对质量没有任何作用。

public static Stream ConvertImage(this Stream originalStream, ImageFormat format)
{
                var image = Image.FromStream(originalStream);

                var stream = new MemoryStream();
                image.Save(stream, format);
                stream.Position = 0;
                return stream;
}

usage:

用法：

var outputStream = gifStream.ConvertImage(ImageFormat.Png);

回答by lupok

Try this:

尝试这个：

       public static class BitmapExtension
       {
          public static void Save(this Bitmap bitmap, String fileName, ImageFormat imageFormat, long quality = 75L)
          {
             using (var encoderParameters = new EncoderParameters(1))
             using (encoderParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality))
             {
                ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

                bitmap.Save(fileName, codecs.Single(codec => codec.FormatID == imageFormat.Guid), encoderParameters);
             }
          }
       }

       ...

       Bitmap bitmap = new Bitmap("myImage.bmp");

       bitmap.Save("myImage.jpg", ImageFormat.Jpeg, 50L);