使用C#如何调整jpeg图像的大小？

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

我正在使用这个：

 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 3

C#（或者更确切地说：.NET 框架）本身不提供此类功能，但它确实为您提供了 System.Drawing 中的位图，以便轻松访问各种图片格式的原始像素数据。其余部分，请参阅http://en.wikipedia.org/wiki/Image_scaling