Question

使用C＃如何调整jpeg图像的大小？代码示例会很棒。

Answer 1

public static class ImageHelper
{
    /// <summary>
    /// Resize the image to the specified width and height.
    /// </summary>
    /// <param name="image">The image to resize.</param>
    /// <param name="width">The width to resize to.</param>
    /// <param name="height">The height to resize to.</param>
    /// <returns>The resized image.</returns>
    public static Bitmap ResizeImage(Image image, int width, int height)
    {
        var destRect = new Rectangle(0, 0, width, height);
        var destImage = new Bitmap(width, height);

        destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution);

        using (var graphics = Graphics.FromImage(destImage))
        {
            graphics.CompositingMode = CompositingMode.SourceCopy;
            graphics.CompositingQuality = CompositingQuality.HighQuality;
            graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
            graphics.SmoothingMode = SmoothingMode.HighQuality;
            graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

            using (var wrapMode = new ImageAttributes())
            {
                wrapMode.SetWrapMode(WrapMode.TileFlipXY);
                graphics.DrawImage(image, destRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, wrapMode);
            }
        }

        return destImage;
    }

    public static Bitmap ResizeImage(Image image, decimal percentage)
    {
        int width = (int)Math.Round(image.Width * percentage, MidpointRounding.AwayFromZero);
        int height = (int)Math.Round(image.Height * percentage, MidpointRounding.AwayFromZero);
        return ResizeImage(image, width, height);
    }
}

class Program
{
    static void Main(string[] args)
    {
        string fileName = @"C:\Images\MyImage.jpg";
        FileInfo info = new FileInfo(fileName);
        using (Image image = Image.FromFile(fileName))
        {
            using(Bitmap resizedImage = ImageHelper.ResizeImage(image, 0.25m))
            {
                resizedImage.Save(
                    info.DirectoryName + "\\" 
                        + info.Name.Substring(0, info.Name.LastIndexOf(info.Extension)) 
                        + "_" + resizedImage.Width + "_" + resizedImage.Height 
                        + info.Extension, 
                    ImageFormat.Jpeg);
            }
        }
    }
}

Answer 2

C＃（或更确切地说：.NET框架）本身并不提供这样的功能，但它确实为您提供System.Drawing的Bitmap，以便轻松访问各种图片格式的原始像素数据。其他方面，请参阅http://en.wikipedia.org/wiki/Image_scaling

Answer 3

良好的免费调整大小过滤器和示例代码。

http://code.google.com/p/zrlabs-yael/

    private void MakeResizedImage(string fromFile, string toFile, int maxWidth, int maxHeight)
    {
        int width;
        int height;

        using (System.Drawing.Image image = System.Drawing.Image.FromFile(fromFile))
        {
            DetermineResizeRatio(maxWidth, maxHeight, image.Width, image.Height, out width, out height);

            using (System.Drawing.Image thumbnailImage = image.GetThumbnailImage(width, height, new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero))
            {
                if (image.Width < thumbnailImage.Width && image.Height < thumbnailImage.Height)
                    File.Copy(fromFile, toFile);
                else
                {
                    ImageCodecInfo ec = GetCodecInfo();
                    EncoderParameters parms = new EncoderParameters(1);
                    parms.Param[0] = new EncoderParameter(Encoder.Compression, 40);

                    ZRLabs.Yael.BasicFilters.ResizeFilter rf = new ZRLabs.Yael.BasicFilters.ResizeFilter();
                    //rf.KeepAspectRatio = true;
                    rf.Height = height;
                    rf.Width = width;

                    System.Drawing.Image img = rf.ExecuteFilter(System.Drawing.Image.FromFile(fromFile));
                    img.Save(toFile, ec, parms);
                }
            }
        }
    }

Answer 4

我正在使用它：

 public static void ResizeJpg(string path, int nWidth, int nHeight)
    {
        using (var result = new Bitmap(nWidth, nHeight))
        {
            using (var input = new Bitmap(path))
            {
                using (Graphics g = Graphics.FromImage((System.Drawing.Image)result))
                {
                    g.DrawImage(input, 0, 0, nWidth, nHeight);
                }
            }

            var ici = ImageCodecInfo.GetImageEncoders().FirstOrDefault(ie => ie.MimeType == "image/jpeg");
            var eps = new EncoderParameters(1);
            eps.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);
            result.Save(path, ici, eps);
        }
    }

Answer 5

很好的例子。

public static Image ResizeImage(Image sourceImage, int maxWidth, int maxHeight)
{
    // Determine which ratio is greater, the width or height, and use
    // this to calculate the new width and height. Effectually constrains
    // the proportions of the resized image to the proportions of the original.
    double xRatio = (double)sourceImage.Width / maxWidth;
    double yRatio = (double)sourceImage.Height / maxHeight;
    double ratioToResizeImage = Math.Max(xRatio, yRatio);
    int newWidth = (int)Math.Floor(sourceImage.Width / ratioToResizeImage);
    int newHeight = (int)Math.Floor(sourceImage.Height / ratioToResizeImage);

    // Create new image canvas -- use maxWidth and maxHeight in this function call if you wish
    // to set the exact dimensions of the output image.
    Bitmap newImage = new Bitmap(newWidth, newHeight, PixelFormat.Format32bppArgb);

    // Render the new image, using a graphic object
    using (Graphics newGraphic = Graphics.FromImage(newImage))
    {
        using (var wrapMode = new ImageAttributes())
        {
            wrapMode.SetWrapMode(WrapMode.TileFlipXY);
            newGraphic.DrawImage(image, destRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, wrapMode);
        }

        // Set the background color to be transparent (can change this to any color)
        newGraphic.Clear(Color.Transparent);

        // Set the method of scaling to use -- HighQualityBicubic is said to have the best quality
        newGraphic.InterpolationMode = InterpolationMode.HighQualityBicubic;

        // Apply the transformation onto the new graphic
        Rectangle sourceDimensions = new Rectangle(0, 0, sourceImage.Width, sourceImage.Height);
        Rectangle destinationDimensions = new Rectangle(0, 0, newWidth, newHeight);
        newGraphic.DrawImage(sourceImage, destinationDimensions, sourceDimensions, GraphicsUnit.Pixel);
    }

    // Image has been modified by all the references to it's related graphic above. Return changes.
    return newImage;
}

来源：http://mattmeisinger.com/resize-image-c-sharp

Answer 6

ImageMagick 应该是最好的方法。简单可靠。

using (var image = new MagickImage(imgfilebuf))
{
    image.Resize(len, len);
    image.Strip();
    using MemoryStream ms = new MemoryStream();
    image.Write(ms);
    return ms.ToArray();
}

使用C＃如何调整jpeg图像的大小？

6 个答案: