Image Resizing Maintaining Height/Width Ratio

• Download source files - 7.31 KB
• Download demo project - 7.31 KB

Introduction

This article explains how to dynamically resize an image in your web page to a given size, maintaining the original height/width ratio. If you have a fixed area where to put an image of an unknown size, you can resize the image to respect the desired width and height limits without stretching it.

Source code

You can download the source code, which contains a simple ASPX web page with three controls: two textboxes, where you can set the maximum width and height of the image, and a button that starts image loading. When you click the button, the page loads the given image (the one included is 450x45 pixels, you can change it programmatically) and resizes it to respect the given limits without stretching it.

The main function of the page is the following:

string COMMONFUNCTIONS_IMAGES_RESIZE_TO_TAG(System.Drawing.Image img, 
                       int MaxWidth, int MaxHeight)
{
    if (img.Width > MaxWidth || img.Height > MaxHeight)
    {
        double widthRatio = (double) img.Width / (double) MaxWidth;
        double heightRatio = (double) img.Height / (double) MaxHeight;
        double ratio = Math.Max(widthRatio, heightRatio);
        int newWidth = (int) (img.Width / ratio);
        int newHeight = (int) (img.Height / ratio);
        return " width=\"" + newWidth.ToString() + "\"" + 
               " height=\"" + newHeight.ToString() + "\" ";
    }
    else
    {
        return "";
    }
}

This function has the following parameters:

• img: the System.Drawing.Image to resize.
• MaxWidth: the maximum width (taken from the textbox).
• MaxHeight: the maximum height (taken from the textbox).

It returns a string in the following format: " width="100" height="50" ".

You can put this piece of code where useful, for example, in an img tag.

How to run the app

Unzip and run the .aspx file using IIS, or another web server like Cassini or WebMatrix.

Feel free to use this code in your web pages.