How to Resize and Optimise Images Using GIMP

Resizing images is one of the many common tasks that people often need to do on a regular basis. Many websites do not accept high resolution images, so it’s very useful to learn how to do this.

In this tutorial I will demonstrate how to resize an image using GIMP, a free image manipulation program available for Linux, OS X and Windows.

Here’s the image I will be using.


As you can see, it is 4096 x 3072 pixels in dimensions and 3.3MB in file size. This is definitely too large for use on the web. We will resize it to something more manageable in the steps listed below.

Make sure you have GIMP installed on your computer. If you’re on Ubuntu or an Ubuntu-based Linux distribution, GIMP should be in the official repositories. Simply run the following command to install it:

sudo apt-get install gimp

For others, simply Google for how to install GIMP on your operating system. The current stable version is 2.8.

Once you have GIMP installed, you’ll need to install the “Save for Web” plugin which helps to optimise images for use on the Web. Please follow the instructions described here to enable the “Save for Web” feature in GIMP for Ubuntu and Windows users.

Once you have satisfied the above dependencies, you may proceed with the steps outlined below.

1. Launch GIMP and go to “File -> Open” or press “Ctrl + O” on your keyboard to open the image you want to resize.

2. From the menu go to “Image -> Scale Image.” A dialog will appear where you can choose new pixel dimensions for your image.


3. To change the values, simply click inside any of the boxes (width or height), and enter your preferred values. In this case I will use 800px as the new width, but use whatever you want.

4. Once you’ve entered the new width, the height will automatically scale down to match the aspect ratio which is fine. In this case the height of the image scaled to 600px from 3072px.


5. If you don’t want to keep the aspect ratio, you can click the icon highlighted with the blue arrow above to change the width and height of your image separately, but keep in mind that this could distort your image.

6. Once you’re satisfied with the new dimensions, you can click the “Scale” button to resize the image to the new pixel values.

7. Now we have a perfectly sized image at 800 x 600 pixels. At this point, the file size should dramatically reduce as well.

8. You can now save your image using the “Save for Web” plugin which you can access via “File -> Save for Web.” The default file format is JPEG which will give you the lowest file size.


9. There’s no ideal quality value, so use your discretion. The preview exists to show you how the image looks as you continue to tweak the options. If you reduce the quality to a very low value, the image will become blurred and unusable.

10. As soon as you’re satisfied with the image quality and file size, you can now save the image in your preferred directory. It is advisable to keep the original file in case you need it later.


As you can see from this example, the image size and dimensions are much smaller, but the quality still remains pretty consistent.

I hope this tutorial has helped you figure out how to properly resize your images with GIMP. If you have any other questions or suggestions on how the methods described in this article can be improved, please leave a comment below.

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