C# 减少任何图像大小 计划

我需要减少图像大小，同时保持一些质量。 但是，我接受GIF、JPEG、JPG和PNG

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现状 上传的图像功能齐全，我已经能够成功地缩放其宽度和/或高度

我找到了一个，这给了我一个非常好的代码示例：

Image myImage = //... load the image somehow 

//以50%的质量保存图像 SaveJpeg（destImagePath，myImage，50）； //加上这个！ 使用系统、绘图、成像

                      /// <summary> 
    /// Saves an image as a jpeg image, with the given quality 
    /// </summary> 
    /// <param name="path">Path to which the image would be saved.</param> 
    // <param name="quality">An integer from 0 to 100, with 100 being the 
    /// highest quality</param> 
    public static void SaveJpeg (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 (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); 
    } 

    /// <summary> 
    /// Returns the image codec with the given mime type 
    /// </summary> 
    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; 
    } 

//
///将图像保存为具有给定质量的jpeg图像
///  
///图像将保存到的路径。
//0到100之间的整数，其中100是
///最高质量
公共静态void SaveJpeg（字符串路径、图像img、整数质量）
{ 
if（质量100）
抛出新ArgumentOutOfRangeException（“质量必须介于0和100之间”）；
//用于图像质量的编码器参数
编码器参数qualityParam=
新编码器参数（编码器、质量、质量）；
//Jpeg图像编解码器
ImageCodecInfo jpegCodec=GetEncoderInfo（“图像/jpeg”）；
EncoderParameters encoderParams=新的EncoderParameters（1）；
encoderParams.Param[0]=qualityParam；
保存（路径、JPEG编解码器、编码器参数）；
} 
///  
///返回具有给定mime类型的图像编解码器
///  
私有静态ImageCodeInfo GetEncoderInfo（字符串mimeType）
{ 
//获取所有图像格式的图像编解码器
ImageCodecInfo[]codecs=ImageCodecInfo.GetImageEncoders（）；
//找到正确的图像编解码器
对于（int i=0；i首先，JPEG使用“有损”压缩算法，这就是为什么可以调整质量。质量越低，压缩效果越好，但数据丢失率越高。此外，还应意识到JPEG格式是为类似照片的图像设计的，将JPEG应用于其他类型的图像可能会令人失望（谷歌）“jpeg伪影”）

PNG和GIF是无损的，因此它们不能支持质量参数。这并不是说你不能从它们中获得更好的压缩效果-有各种各样的工具可以减小PNG的大小（pngcrush、punypng等），但是这些工具（大部分）工作方式与JPEG压缩器完全不同。需要注意的是，GIF支持比PNG更小的调色板，最多只能支持256种颜色

因此，请按顺序回答您的问题：

无法进行真正的比较，因为JPEG压缩有一个折衷，而PNG和GIF压缩没有，折衷的程度取决于图像的类型。也就是说，JPEG通常会提供更好的压缩，但如果图像不是照片，结果会明显变差

你的JPEG代码很好。谷歌搜索C#-兼容PNG的工具

你需要尝试你期望的图像类型

对

您可能想阅读我的文章。它涵盖了您的4个问题中的3个。
我们可以通过不同的方式来实现这一点

最好的方法之一是将所有图像转换为jpeg格式，因为它将以较小的大小提供更好的清晰度，在这种情况下，我们不需要更改特定图像的任何高度或宽度

方法1：将所有图像转换为jpeg（无需额外压缩）

方法2：通过更改图像的高度和宽度（无jpeg转换）

CommonConstant.CS

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace EmptyDemo.compression
{
#region[Directive]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
#endregion[Directive]

/// <summary>
/// This class is used to get the constants
/// </summary>
public class CommonConstant
{
    public const string JPEG = ".jpeg";
    public const string PNG = ".png";
    public const string JPG = ".jpg";
    public const string BTM = ".btm";
}
}

我使用同样的概念来调整图片的大小，而不只是通过改变比例因子来降低质量。在社交网站上传图片后，他们会缩小图片的大小，但在看到我试图写这篇文章后，质量将是相同的

using System.Drawing.Imaging;
using System.Drawing;

public partial class Default3 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        VaryQualityLevel();
    }
    private void VaryQualityLevel()
    {
        Bitmap bmp1 = new Bitmap(Server.MapPath("test2.png"));
        ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);
        System.Drawing.Imaging.Encoder myEncoder =System.Drawing.Imaging.Encoder.Quality;
        EncoderParameters myEncoderParameters = new EncoderParameters(1);
        EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 50L);
        myEncoderParameters.Param[0] = myEncoderParameter;
        bmp1.Save(Server.MapPath("~/Images/1.jpg"), jgpEncoder, myEncoderParameters);
        //myEncoderParameter = new EncoderParameter(myEncoder, 75L);
        //myEncoderParameters.Param[0] = myEncoderParameter;
        //bmp1.Save(Server.MapPath("~/Images/2.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;
    }
}

GIF和PNG通过减少颜色进行压缩。对于Photoshot来说，颜色信息的丢失是非常明显的。是的，我不想减少像素深度，这可能是有效的，但也可能是明显的。我在考虑更多的是使用不同的gzip压缩级别。但是你是对的，这种技术要么非常有效，要么无法接受表，具体取决于输入。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace EmptyDemo.compression
{
#region[Directive]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
#endregion[Directive]

/// <summary>
/// This class is used to compress the image to
/// provided size
/// </summary>
public class ImageCompress
{
    #region[PrivateData]
    private static volatile ImageCompress imageCompress;
    private Bitmap bitmap;
    private int width;
    private int height;
    private Image img;
    #endregion[Privatedata]

    #region[Constructor]
    /// <summary>
    /// It is used to restrict to create the instance of the      ImageCompress
    /// </summary>
    private ImageCompress()
    {
    }
    #endregion[Constructor]

    #region[Poperties]
    /// <summary>
    /// Gets ImageCompress object
    /// </summary>
    public static ImageCompress GetImageCompressObject
    {
        get
        {
            if (imageCompress == null)
            {
                imageCompress = new ImageCompress();
            }
            return imageCompress;
        }
    }

    /// <summary>
    /// Gets or sets Width
    /// </summary>
    public int Height
    {
        get { return height; }
        set { height = value; }
    }

    /// <summary>
    /// Gets or sets Width
    /// </summary>
    public int Width
    {
        get { return width; }
        set { width = value; }
    }

    /// <summary>
    /// Gets or sets Image
    /// </summary>
    public Bitmap GetImage
    {
        get { return bitmap; }
        set { bitmap = value; }
    }
    #endregion[Poperties]

    #region[PublicFunction]
    /// <summary>
    /// This function is used to save the image
    /// </summary>
    /// <param name="fileName"></param>
    /// <param name="path"></param>
    public void Save(string fileName, string path)
    {
        if (ISValidFileType(fileName))
        {
            string pathaname = path + @"\" + fileName;
            save(pathaname, 60);
        }
    }
    #endregion[PublicFunction]

    #region[PrivateData]
    /// <summary>
    /// This function is use to compress the image to
    /// predefine size
    /// </summary>
    /// <returns>return bitmap in compress size</returns>
    private Image CompressImage()
    {
        if (GetImage != null)
        {
            Width = (Width == 0) ? GetImage.Width : Width;
            Height = (Height == 0) ? GetImage.Height : Height;
            Bitmap newBitmap = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);
            newBitmap = bitmap;
            newBitmap.SetResolution(80, 80);
            return newBitmap.GetThumbnailImage(Width, Height, null, IntPtr.Zero);
        }
        else
        {
            throw new Exception("Please provide bitmap");
        }
    }

    /// <summary>
    /// This function is used to check the file Type
    /// </summary>
    /// <param name="fileName">String data type:contain the file name</param>
    /// <returns>true or false on the file extention</returns>
    private bool ISValidFileType(string fileName)
    {
        bool isValidExt = false;
        string fileExt = Path.GetExtension(fileName);
        switch (fileExt.ToLower())
        {
            case CommonConstant.JPEG:
            case CommonConstant.BTM:
            case CommonConstant.JPG:
            case CommonConstant.PNG:
                isValidExt = true;
                break;
        }
        return isValidExt;
    }

    /// <summary>
    /// This function is used to get the imageCode info
    /// on the basis of mimeType
    /// </summary>
    /// <param name="mimeType">string data type</param>
    /// <returns>ImageCodecInfo data type</returns>
    private ImageCodecInfo GetImageCoeInfo(string mimeType)
    {
        ImageCodecInfo[] codes = ImageCodecInfo.GetImageEncoders();
        for (int i = 0; i < codes.Length; i++)
        {
            if (codes[i].MimeType == mimeType)
            {
                return codes[i];
            }
        }
        return null;
    }
    /// <summary>
    /// this function is used to save the image into a
    /// given path
    /// </summary>
    /// <param name="path">string data type</param>
    /// <param name="quality">int data type</param>
    private void save(string path, int quality)
    {
        img = CompressImage();
        ////Setting the quality of the picture
        EncoderParameter qualityParam =
            new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
        ////Seting the format to save
        ImageCodecInfo imageCodec = GetImageCoeInfo("image/jpeg");
        ////Used to contain the poarameters of the quality
        EncoderParameters parameters = new EncoderParameters(1);
        parameters.Param[0] = qualityParam;
        ////Used to save the image to a  given path
        img.Save(path, imageCodec, parameters);
    }
    #endregion[PrivateData]
}
}

    [WebMethod]
    public void UploadFile()
     {
         if (HttpContext.Current.Request.Files.AllKeys.Any())
         {
             // Get the uploaded image from the Files collection
             var httpPostedFile = HttpContext.Current.Request.Files["UploadedImage"];
             if (httpPostedFile != null)
             {
                 ImageCompress imgCompress = ImageCompress.GetImageCompressObject;
                 imgCompress.GetImage = new System.Drawing.Bitmap(httpPostedFile.InputStream);
                 imgCompress.Height = 260;
                 imgCompress.Width = 358;
                 //imgCompress.Save(httpPostedFile.FileName, @"C:\Documents and Settings\Rasmi\My Documents\Visual Studio2008\WebSites\compressImageFile\Logo");
                 imgCompress.Save(httpPostedFile.FileName, HttpContext.Current.Server.MapPath("~/Download/"));

             }
         }
     }

using System.Drawing.Imaging;
using System.Drawing;

public partial class Default3 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        VaryQualityLevel();
    }
    private void VaryQualityLevel()
    {
        Bitmap bmp1 = new Bitmap(Server.MapPath("test2.png"));
        ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);
        System.Drawing.Imaging.Encoder myEncoder =System.Drawing.Imaging.Encoder.Quality;
        EncoderParameters myEncoderParameters = new EncoderParameters(1);
        EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 50L);
        myEncoderParameters.Param[0] = myEncoderParameter;
        bmp1.Save(Server.MapPath("~/Images/1.jpg"), jgpEncoder, myEncoderParameters);
        //myEncoderParameter = new EncoderParameter(myEncoder, 75L);
        //myEncoderParameters.Param[0] = myEncoderParameter;
        //bmp1.Save(Server.MapPath("~/Images/2.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;
    }
}