Redimensionner une image en asp.net sans perdre la qualité de l'image

Question

Je développe une application web ASP.NET 3.5 dans laquelle je permets à mes utilisateurs de télécharger des images jpeg, gif, bmp ou png. Si les dimensions de l'image téléchargée sont supérieures à 103 x 32, je veux redimensionner l'image téléchargée à 103 x 32. J'ai lu quelques billets de blog et articles, et j'ai également essayé certains des exemples de code, mais rien ne semble fonctionner correctement. Quelqu'un a-t-il réussi à le faire ?

Answer 1

Voici le code que j'utilise. Il prend en charge la rotation et définit également la résolution de l'image aux normes JPEG de 72dpi@24-bit color (par défaut, GDI+ enregistre les images à 96dpi@32-bit color). Il corrige également le problème de bordure noire/grise que certaines personnes rencontrent lors du redimensionnement des images.

/// <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

J'ai eu le même problème il y a quelque temps et je l'ai résolu de cette façon :

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);
}

Je viens de lire que c'était le moyen d'obtenir la meilleure qualité.

Answer 3

Le code associé au redimensionnement effectif du bitmap est le suivant.

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;
}
}

Cet article de blog contient le code source complet pour le redimensionnement et la compression des images (si nécessaire).

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

Answer 4

J'ai réussi à le faire en créant un bitmap de l'image, puis en redimensionnant ce bitmap... Je ne suis pas sûr que ce soit la meilleure façon de procéder, mais ça marche pour moi.

Dans mon cas, j'ai dû réduire de moitié la hauteur et la largeur de l'image.

Voilà ce que j'ai fait.

   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;
    }

Answer 5

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;
    }