Resize image proportionally with MaxHeight and MaxWidth constraints

Question

Using System.Drawing.Image.

If an image width or height exceed the maximum, it need to be resized proportionally . After resized it need to make sure that neither width or height still exceed the limit.

The Width and Height will be resized until it is not exceed to maximum and minimum automatically (biggest size possible) and also maintain the ratio.

Answer 1

Like this?

public static void Test()
{
    using (var image = Image.FromFile(@"c:\logo.png"))
    using (var newImage = ScaleImage(image, 300, 400))
    {
        newImage.Save(@"c:\test.png", ImageFormat.Png);
    }
}

public static Image ScaleImage(Image image, int maxWidth, int maxHeight)
{
    var ratioX = (double)maxWidth / image.Width;
    var ratioY = (double)maxHeight / image.Height;
    var ratio = Math.Min(ratioX, ratioY);

    var newWidth = (int)(image.Width * ratio);
    var newHeight = (int)(image.Height * ratio);

    var newImage = new Bitmap(newWidth, newHeight);

    using (var graphics = Graphics.FromImage(newImage))
        graphics.DrawImage(image, 0, 0, newWidth, newHeight);

    return newImage;
}

Answer 2

Much longer solution, but accounts for the following scenarios:

1. Is the image smaller than the bounding box?
2. Is the Image and the Bounding Box square?
3. Is the Image square and the bounding box isn't
4. Is the image wider and taller than the bounding box
5. Is the image wider than the bounding box

6. Is the image taller than the bounding box

   private Image ResizePhoto(FileInfo sourceImage, int desiredWidth, int desiredHeight)
   {
       //throw error if bouning box is to small
       if (desiredWidth < 4 || desiredHeight < 4)
           throw new InvalidOperationException("Bounding Box of Resize Photo must be larger than 4X4 pixels.");            
       var original = Bitmap.FromFile(sourceImage.FullName);
   
       //store image widths in variable for easier use
       var oW = (decimal)original.Width;
       var oH = (decimal)original.Height;
       var dW = (decimal)desiredWidth;
       var dH = (decimal)desiredHeight;
   
       //check if image already fits
       if (oW < dW && oH < dH)
           return original; //image fits in bounding box, keep size (center with css) If we made it bigger it would stretch the image resulting in loss of quality.
   
       //check for double squares
       if (oW == oH && dW == dH)
       {
           //image and bounding box are square, no need to calculate aspects, just downsize it with the bounding box
           Bitmap square = new Bitmap(original, (int)dW, (int)dH);
           original.Dispose();
           return square;
       }
   
       //check original image is square
       if (oW == oH)
       {
           //image is square, bounding box isn't.  Get smallest side of bounding box and resize to a square of that center the image vertically and horizontally with Css there will be space on one side.
           int smallSide = (int)Math.Min(dW, dH);
           Bitmap square = new Bitmap(original, smallSide, smallSide);
           original.Dispose();
           return square;
       }
   
       //not dealing with squares, figure out resizing within aspect ratios            
       if (oW > dW && oH > dH) //image is wider and taller than bounding box
       {
           var r = Math.Min(dW, dH) / Math.Min(oW, oH); //two dimensions so figure out which bounding box dimension is the smallest and which original image dimension is the smallest, already know original image is larger than bounding box
           var nH = oH * r; //will downscale the original image by an aspect ratio to fit in the bounding box at the maximum size within aspect ratio.
           var nW = oW * r;
           var resized = new Bitmap(original, (int)nW, (int)nH);
           original.Dispose();
           return resized;
       }
       else
       {
           if (oW > dW) //image is wider than bounding box
           {
               var r = dW / oW; //one dimension (width) so calculate the aspect ratio between the bounding box width and original image width
               var nW = oW * r; //downscale image by r to fit in the bounding box...
               var nH = oH * r;
               var resized = new Bitmap(original, (int)nW, (int)nH);
               original.Dispose();
               return resized;
           }
           else
           {
               //original image is taller than bounding box
               var r = dH / oH;
               var nH = oH * r;
               var nW = oW * r;
               var resized = new Bitmap(original, (int)nW, (int)nH);
               original.Dispose();
               return resized;
           }
       }
   }
   

Answer 3

Working Solution :

For Resize image with size lower then 100Kb

WriteableBitmap bitmap = new WriteableBitmap(140,140);
bitmap.SetSource(dlg.File.OpenRead());
image1.Source = bitmap;

Image img = new Image();
img.Source = bitmap;
WriteableBitmap i;

do
{
    ScaleTransform st = new ScaleTransform();
    st.ScaleX = 0.3;
    st.ScaleY = 0.3;
    i = new WriteableBitmap(img, st);
    img.Source = i;
} while (i.Pixels.Length / 1024 > 100);

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