C# 在 asp.net 中调整图像大小而不会降低图像质量

Resizing an image in asp.net without losing the image quality

提问by Kumar

I am developing an ASP.NET 3.5 web application in which I am allowing my users to upload either jpeg,gif,bmp or png images. If the uploaded image dimensions are greater then 103 x 32 the I want to resize the uploaded image to 103 x 32. I have read some blog posts and articles, and have also tried some of the code samples but nothing seems to work right. Has anyone succeed in doing this?

我正在开发一个 ASP.NET 3.5 web 应用程序，我允许我的用户上传 jpeg、gif、bmp 或 png 图像。如果上传的图像尺寸大于 103 x 32，我想将上传的图像调整为 103 x 32。我阅读了一些博客文章和文章，也尝试了一些代码示例，但似乎没有任何效果。有没有人成功做到这一点？

采纳答案by Alxandr

I had the same problem a while back and dealt with it this way:

不久前我遇到了同样的问题，并以这种方式处理：

private Image RezizeImage(Image img, int maxWidth, int maxHeight)
{
    if(img.Height < maxHeight && img.Width < maxWidth) return img;
    using (img)
    {
        Double xRatio = (double)img.Width / maxWidth;
        Double yRatio = (double)img.Height / maxHeight;
        Double ratio = Math.Max(xRatio, yRatio);
        int nnx = (int)Math.Floor(img.Width / ratio);
        int nny = (int)Math.Floor(img.Height / ratio);
        Bitmap cpy = new Bitmap(nnx, nny, PixelFormat.Format32bppArgb);
        using (Graphics gr = Graphics.FromImage(cpy))
        {
            gr.Clear(Color.Transparent);

            // This is said to give best quality when resizing images
            gr.InterpolationMode = InterpolationMode.HighQualityBicubic;

            gr.DrawImage(img,
                new Rectangle(0, 0, nnx, nny),
                new Rectangle(0, 0, img.Width, img.Height),
                GraphicsUnit.Pixel);
        }
        return cpy;
    }

}

private MemoryStream BytearrayToStream(byte[] arr)
{
    return new MemoryStream(arr, 0, arr.Length);
}

private void HandleImageUpload(byte[] binaryImage)
{
    Image img = RezizeImage(Image.FromStream(BytearrayToStream(binaryImage)), 103, 32);
    img.Save("IMAGELOCATION.png", System.Drawing.Imaging.ImageFormat.Gif);
}

I just read that this was the the way to get highest quality.

我刚刚读到这是获得最高质量的方法。

回答by Aaron

I've successfully done this by creating a bitmap of the image and then resizing the bitmap...I'm not sure if this is the best or most efficient way of doing this, but it works for me.

我通过创建图像的位图，然后调整位图的大小，成功地做到了这一点......我不确定这是否是最好的或最有效的方法，但它对我有用。

In my case, I needed to cut the height and width of the image by half.

就我而言，我需要将图像的高度和宽度减半。

Here's what I did.

这就是我所做的。

   private Image getImageFromBytes(byte[] myByteArray)
    {                        
        System.IO.MemoryStream newImageStream = new System.IO.MemoryStream(myByteArray, 0, myByteArray.Length);
        Image image = Image.FromStream(newImageStream, true);
        Bitmap resized = new Bitmap(image, image.Width / 2, image.Height / 2);
        image.Dispose();
        newImageStream.Dispose();
        return resized;
    }

回答by Daniel T.

This is the code I use. It supports rotation, and also sets the image resolution to the JPEG standards of 72dpi@24-bit color (by default GDI+ saves images at 96dpi@32-bit color). It also fixes the black/gray border problem that some people experience when resizing images.

这是我使用的代码。它支持旋转，还将图像分辨率设置为 72dpi@24 位色的 JPEG 标准（默认情况下，GDI+ 以 96dpi@32 位色保存图像）。它还修复了某些人在调整图像大小时遇到​​的黑色/灰色边框问题。

/// <summary>
/// Resizes and rotates an image, keeping the original aspect ratio. Does not dispose the original
/// Image instance.
/// </summary>
/// <param name="image">Image instance</param>
/// <param name="width">desired width</param>
/// <param name="height">desired height</param>
/// <param name="rotateFlipType">desired RotateFlipType</param>
/// <returns>new resized/rotated Image instance</returns>
public static Image Resize(Image image, int width, int height, RotateFlipType rotateFlipType)
{
    // clone the Image instance, since we don't want to resize the original Image instance
    var rotatedImage = image.Clone() as Image;
    rotatedImage.RotateFlip(rotateFlipType);
    var newSize = CalculateResizedDimensions(rotatedImage, width, height);

    var resizedImage = new Bitmap(newSize.Width, newSize.Height, PixelFormat.Format32bppArgb);
    resizedImage.SetResolution(72, 72);

    using (var graphics = Graphics.FromImage(resizedImage))
    {
        // set parameters to create a high-quality thumbnail
        graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
        graphics.SmoothingMode = SmoothingMode.AntiAlias;
        graphics.CompositingQuality = CompositingQuality.HighQuality;
        graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

        // use an image attribute in order to remove the black/gray border around image after resize
        // (most obvious on white images), see this post for more information:
        // http://www.codeproject.com/KB/GDI-plus/imgresizoutperfgdiplus.aspx
        using (var attribute = new ImageAttributes())
        {
            attribute.SetWrapMode(WrapMode.TileFlipXY);

            // draws the resized image to the bitmap
            graphics.DrawImage(rotatedImage, new Rectangle(new Point(0, 0), newSize), 0, 0, rotatedImage.Width, rotatedImage.Height, GraphicsUnit.Pixel, attribute);
        }
    }

    return resizedImage;
}

/// <summary>
/// Calculates resized dimensions for an image, preserving the aspect ratio.
/// </summary>
/// <param name="image">Image instance</param>
/// <param name="desiredWidth">desired width</param>
/// <param name="desiredHeight">desired height</param>
/// <returns>Size instance with the resized dimensions</returns>
private static Size CalculateResizedDimensions(Image image, int desiredWidth, int desiredHeight)
{
    var widthScale = (double)desiredWidth / image.Width;
    var heightScale = (double)desiredHeight / image.Height;

    // scale to whichever ratio is smaller, this works for both scaling up and scaling down
    var scale = widthScale < heightScale ? widthScale : heightScale;

    return new Size
                   {
                       Width = (int) (scale * image.Width),
                       Height = (int) (scale * image.Height)
                   };
}

回答by gb2d

The code associated with the actual resizing of the bitmap is as follows.

与位图实际调整大小相关的代码如下。

public static Bitmap ResizeBitmap( Bitmap originalBitmap, int requiredHeight, int requiredWidth )
{
   int[] heightWidthRequiredDimensions;

   // Pass dimensions to worker method depending on image type required
   heightWidthRequiredDimensions = WorkDimensions(originalBitmap.Height, originalBitmap.Width, requiredHeight, requiredWidth);


   Bitmap resizedBitmap = new Bitmap( heightWidthRequiredDimensions[1],
                                      heightWidthRequiredDimensions[0] );

   const float resolution = 72;

   resizedBitmap.SetResolution( resolution, resolution );

   Graphics graphic = Graphics.FromImage( (Image) resizedBitmap );

   graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
   graphic.DrawImage( originalBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height );

   graphic.Dispose();
   originalBitmap.Dispose();
   //resizedBitmap.Dispose(); // Still in use


   return resizedBitmap;
}


private static int[] WorkDimensions(int originalHeight, int originalWidth, int requiredHeight, int requiredWidth )
{
   int imgHeight = 0;
   int imgWidth = 0;

   imgWidth = requiredHeight;
   imgHeight = requiredWidth;


   int requiredHeightLocal = originalHeight;
   int requiredWidthLocal = originalWidth;

   double ratio = 0;

   // Check height first
   // If original height exceeds maximum, get new height and work ratio.
   if ( originalHeight > imgHeight )
   {
       ratio = double.Parse( ( (double) imgHeight / (double) originalHeight ).ToString() );
       requiredHeightLocal = imgHeight;
       requiredWidthLocal = (int) ( (decimal) originalWidth * (decimal) ratio );
   }

   // Check width second. It will most likely have been sized down enough
   // in the previous if statement. If not, change both dimensions here by width.
   // If new width exceeds maximum, get new width and height ratio.
   if ( requiredWidthLocal >= imgWidth )
   {
       ratio = double.Parse( ( (double) imgWidth / (double) originalWidth ).ToString() );
       requiredWidthLocal = imgWidth;
       requiredHeightLocal = (int) ( (double) originalHeight * (double) ratio );
   }

   int[] heightWidthDimensionArr = { requiredHeightLocal, requiredWidthLocal };

   return heightWidthDimensionArr;
}
}

This blog post contains full source code for image resizing, and compression (if required)

这篇博文包含用于调整图像大小和压缩（如果需要）的完整源代码

http://blog.bombdefused.com/2010/08/bulk-image-optimizer-in-c-full-source.html

http://blog.bombdefused.com/2010/08/bulk-image-optimizer-in-c-full-source.html

回答by JIYAUL MUSTAPHA

public static System.Drawing.Image ScaleImage(System.Drawing.Image image, int maxImageHeight)
    {
        /* we will resize image based on the height/width ratio by passing expected height as parameter. Based on Expected height and current image height, new ratio will be arrived and using the same we will do the resizing of image width. */

        var ratio = (double)maxImageHeight / image.Height;
        var newWidth = (int)(image.Width * ratio);
        var newHeight = (int)(image.Height * ratio);
        var newImage = new Bitmap(newWidth, newHeight);
        using (var g = Graphics.FromImage(newImage))
        {
            g.DrawImage(image, 0, 0, newWidth, newHeight);
        }
        return newImage;
    }

回答by Arul Shankar Rajendran

  decimal size = Math.Round(((decimal)fUpload.PostedFile.ContentLength / (decimal)1024), 2);
        DirectoryInfo dir = new DirectoryInfo(MapPath("Images"));
        FileInfo[] files = dir.GetFiles();
         foreach (FileInfo info in files)
        {
              decimal size2 = Math.Round(((decimal)info.Length / (decimal)1024), 2);
              string Image_name = info.Name.ToString();
              string targetPath = Server.MapPath("Images/" + Image_name);
              string strm = Server.MapPath("Images/" + Image_name);
              var targetFile = targetPath;
              ReduceImageSize(0.5, strm, targetFile, Image_name);
         }

回答by Arul Shankar Rajendran

   // Fixed Size Image Generate Code
 protected void btnUpload_Click(object sender, EventArgs e)
    {

 decimal size = Math.Round(((decimal)fUpload.PostedFile.ContentLength / (decimal)1024), 2);
        DirectoryInfo dir = new DirectoryInfo(MapPath("Images"));
        FileInfo[] files = dir.GetFiles();
         foreach (FileInfo info in files)
        {
              decimal size2 = Math.Round(((decimal)info.Length / (decimal)1024), 2);
              string Image_name = info.Name.ToString();
              string targetPath = Server.MapPath("Images/" + Image_name);
              string strm = Server.MapPath("Images/" + Image_name);
              var targetFile = targetPath;
              ReduceImageSize(0.5, strm, targetFile, Image_name);
         }
}

 public void ReduceImageSize(double scaleFactor, String sourcePath, string targetPath, string Image_name)
    {

 // Fixed Size Image Generate Code

       public void ReduceImageSize(double scaleFactor, String sourcePath, string targetPath, string Image_name)
    {
        using (var image = System.Drawing.Image.FromFile(sourcePath))
               {

            //var newWidth = (int)(image.Width  * scaleFactor);
            //var newHeight = (int)(image.Height * scaleFactor);
            var newWidth = (int)(500 * scaleFactor);
            var newHeight = (int)(500 * scaleFactor);
            var thumbnailImg = new Bitmap(newWidth, newHeight);
            var thumbGraph = Graphics.FromImage(thumbnailImg);
            thumbGraph.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            thumbGraph.SmoothingMode = SmoothingMode.HighQuality;
            thumbGraph.InterpolationMode = InterpolationMode.HighQualityBicubic;
            var imageRectangle = new System.Drawing.RectangleF (0, 0, newWidth, newHeight);
            thumbGraph.DrawImage(image, imageRectangle);


            MemoryStream s = new MemoryStream();
            thumbnailImg.Save(s, System.Drawing.Imaging.ImageFormat.Png);
            s.Position = 0;
            byte[] image2 = new byte[525000];// 512kb =525000  
            s.Read(image2, 0, image2.Length);

            Guid guid = Guid.NewGuid();
            string Server_MapPath = Server.MapPath("~/Image Compress/" + Image_name + guid.ToString() + ".PNG");//Your Compressor Image Save Path

            System.IO.FileStream fs = new System.IO.FileStream(Server_MapPath, System.IO.FileMode.Create, System.IO.FileAccess.ReadWrite);
            fs.Write(image2, 0, image2.Length);

        }
    }