By Sarawut Positwinyu

2011-06-28 05:06:20 8 Comments

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.


@Ryan Mann 2015-10-01 04:28:09

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);
            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);
            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);
            return resized;
            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);
                return resized;
                //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);
                return resized;

@wloescher 2017-07-21 19:55:26

i think there's a couple of typos where you're using the ratio to calculate the new height for resized image. Correct var nH = oH * r; Incorrect: var nH = oW * r;

@Ryan Mann 2019-07-03 14:54:31

Fixed, just never commented.

@Alex Aza 2011-06-28 05:34:19

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;

@Conrad Frix 2011-06-28 05:50:58

@Alex nice use of Math.Min (I always forget about that one)

@Schalk 2011-06-28 07:07:20

I'd suggest you use a using statement on the Graphics object at least to save some resources :)

@Sarawut Positwinyu 2011-06-28 10:37:18

I just thinking about a case, i don't sure if it possible or not that after multiply with ratio the width Or height might still larger than max width or max height.

@Alex Aza 2011-06-28 16:24:30

@Sarawut Positwinyu - Although I can't see it, the code could have a bug. Can you give an example, when it does not work?

@Sarawut Positwinyu 2011-06-29 02:50:40

@Alex Aza, After experimenting your code and trying to make it cause a bug, i have found that it is impossible. The code is so thoughtful.

@Induster 2012-08-18 18:52:01

Also make sure you are using System.Drawing.Image if using

@Ryan Mann 2015-09-30 03:43:54

Correct me If I am wrong.. But if the aspect ratio of the maxWidth and maxHeight is different than the original images aspect ratio, won't this deform the image? The calculation should caclulate a properly aspected resize within the bounding box (maxWidth/maxHeight). Which would result in an image that is smaller than the bounding box in almost all scenarios. This fits the bounding box no matter what, which is wrong most the time.

@brykneval 2015-12-22 15:13:40

@AlexAza can you see this:…

@Andrii Muzychuk 2016-04-15 09:27:12

@AlexAza, I've used your code and added var x = 0; var y = 0; if (newWidth > newHeight) { y = (newWidth - newHeight) / 2; } else if (newHeight > newWidth) { x = (newHeight - newWidth) / 2; } to center scaled image

@Smith 2016-08-24 17:46:28

@AlexAza what about returning the image without saving?

@Alex Aza 2016-08-25 07:29:55

@Smith - don't run Save method if you don't need to save the image. This is exactly what my ScaleImage method does - returns image without saving it.

@user806084 2012-10-03 08:42:59

Working Solution :

For Resize image with size lower then 100Kb

WriteableBitmap bitmap = new WriteableBitmap(140,140);
image1.Source = bitmap;

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

    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);

More Reference at

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