在asp.net中调整图像大小而不会丢失图像质量

Question

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.如果上传的图片尺寸大于103 x 32,我想将上传的图片大小调整为103 x 32.我已经阅读了一些博文和文章,并且还尝试了一些代码示例,但似乎没有什么工作正常.有没有人成功做到这一点？

Answer 1

这是我使用的代码.它支持旋转,并且还将图像分辨率设置为72dpi @ 24位颜色的JPEG标准(默认情况下,GDI +以96dpi @ 32位颜色保存图像).它还修复了一些人在调整图像大小时遇到​​的黑/灰边框问题.

/// <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)
                   };
}

Answer 2

我有一段时间遇到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);
}

我只是读到这是获得最高质量的方法.