In this article, we're going to have a quick shufty at some basic image editing in GIMP. What's that, you say? Well, GIMP stands for GNU Image Manipulation Program – what do you mean it still doesn't make much sense? Anyway, all you need to know about this little image editor is that it's free, and surprisingly powerful given that fact. If you don't already have it, grab the program here, and then get installing.
So you want to resize an image with GIMP? Just a basic resize is an easy process, as you'd hope. Open up your image in GIMP, click on Image along the top menu, then select Scale Image from the drop-down. You can then resize your image by typing in a new number in the Width box, and the number of pixels will automatically be adjusted to keep things in proportion (unless you click on the little chain-link icon on the right of these numbers so the chain is broken – in that case, the numbers won't be kept in proportion, but you'll end up with a stretched/distorted image as a result). Finally, click the Scale button to do just that.
Incidentally, if you'd rather work in, say, percentages rather than pixels, then you can choose new units using the "px" (pixels) drop-down box just to the right of the aforementioned chain-link icon.
Maybe you want to scale your image to a specific size, to fit, say, your blog site? Here are ITProPortal, for example, we use article header images with a 4:3 ratio, so let's do that as an example.
To crop the image to 4:3 (or whatever ratio you want), select the Crop tool (Shift+C) which allows you to draw a box on your picture. To make this box keep to a 4:3 ratio, you'll need to look in the Toolbox window, under the Tool Options section where it says "Crop".
There's a little box next to where it says Fixed (Aspect Ratio) – tick this. Now, click in the box directly underneath where you just ticked, and type in the aspect ratio you want, in this case "4:3" (without the quote marks, of course).
Now you can draw your 4:3 box on the image, adjust it to your liking, then click in the middle of it to crop the picture down to a 4:3 image. You can then scale it to the correct size as we discussed above (via the Scale Image menu).
But what if your image is a non-square shape with so much difference between the vertical and horizontal pixel size that you can't actually fit the central object of the picture fully into the 4:3 box? Say you've got an image of a smartphone on a white background, but when cropping to 4:3 you're cutting the top and bottom bezels off the handset so it looks silly. With a white background, you can simply make that white background larger to give you more space to crop, so you're not chopping bits of the phone off.
To do this, select Image from the top menu, and click Canvas Size. Click the broken chain-link to the right of the Width and Height boxes, so it becomes linked and these measurements are kept in proportion, and then double (or perhaps even treble if you need to create a lot of extra white space) the number in one of them (it doesn't matter which – they'll both double up as they're linked).
Now click the Centre button, and then Resize. Then click Image from the top menu again, and then Flatten Image. You'll now have much more space to draw your 4:3 box, and it should fit (if not, you can make the background even bigger by simply doing this process over again).
Even if you don't have a white background to work with, you can still use this method to crop to 4:3 (or whatever ratio), it's just that you'll have white borders. If you're not keen on that idea, then you'll just have to crop that object down as best you can and live with whatever bits are missing.