ASP.Net MVC Image Upload Resizing by downscaling o

问题:

A user will be able to upload an image. If the image is greater than a set size I want to downsize it to that size. Obviously it doesn't have to match exactly due to ratios, the width would be the key size so the height would be variable.

If the image is smaller than the set size I would like to create a new image to the set size with a background of a defined colour and then centre the uploaded image into it therefore the result is the original with paddded colour.

Any code examples or links greatly appreciated

回答1:

Here's a snippet of code I quickly knocked up for resizing it based on the width. I'm sure you could figure out how to add a background color to the Bitmap. It's not complete code but just an idea of how to do things.

public static void ResizeLogo(string originalFilename, string resizeFilename)
{
    Image imgOriginal = Image.FromFile(originalFilename);

    //pass in whatever value you want for the width (180)
    Image imgActual = ScaleBySize(imgOriginal, 180);
    imgActual.Save(resizeFilename);
    imgActual.Dispose();
}

public static Image ScaleBySize(Image imgPhoto, int size)
{
    int logoSize = size;

    float sourceWidth = imgPhoto.Width;
    float sourceHeight = imgPhoto.Height;
    float destHeight = 0;
    float destWidth = 0;
    int sourceX = 0;
    int sourceY = 0;
    int destX = 0;
    int destY = 0;

    // Resize Image to have the height = logoSize/2 or width = logoSize.
    // Height is greater than width, set Height = logoSize and resize width accordingly
    if (sourceWidth > (2 * sourceHeight))
    {
        destWidth = logoSize;
        destHeight = (float)(sourceHeight * logoSize / sourceWidth);
    }
    else
    {
        int h = logoSize / 2;
        destHeight = h;
        destWidth = (float)(sourceWidth * h / sourceHeight);
    }
    // Width is greater than height, set Width = logoSize and resize height accordingly

    Bitmap bmPhoto = new Bitmap((int)destWidth, (int)destHeight, 
                                PixelFormat.Format32bppPArgb);
    bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

    Graphics grPhoto = Graphics.FromImage(bmPhoto);
    grPhoto.InterpolationMode = InterpolationMode.HighQualityBicubic;

    grPhoto.DrawImage(imgPhoto,
        new Rectangle(destX, destY, (int)destWidth, (int)destHeight),
        new Rectangle(sourceX, sourceY, (int)sourceWidth, (int)sourceHeight),
        GraphicsUnit.Pixel);

    grPhoto.Dispose();

    return bmPhoto;
}

回答2:

You can just load the file into a bitmap object:

http://msdn.microsoft.com/en-us/library/system.drawing.bitmap.aspx

Then just check the width on the object. For the second part of your problem, I would recommend using a tool like ImageMagick

http://www.imagemagick.org/script/index.php

to accurately resize the first image or to create the background image and merge the two images together.