GIMP Image Compression Tutorial

There is no doubt that all of us, at least occasionally, look at photos on the web. Unfortunately, not everyone has very high-speed internet, and this rears its ugly head when we try to load up big images. Today, I’ll show you how to compress images to a much smaller size, using a free image-editing program called GIMP, which you may or may not already be familiar with. It is very similar to Adobe’s Photoshop. I will be shrinking down these images using the shrinking tool in WordPress, however I highly recommend you click on the images to get the full-resolution versions. That will be very helpful during this. So, first, load up your image into GIMP. If you wish to follow along and experiment with slightly different settings, you can find the image I’m using here

Now we’re going to go under the filters menu, to the blur sub-menu, and click on “Selective Gaussian Blur.”

Selective Gaussian Blur is a form of digital noise-reduction intended to remove things such as grain/noise. The main flaw with any form of noise-reduction is that it tends to remove detail, which is why I do not use it on high-quality images, no matter how noisy they are. And, as a matter of fact, I like some grain. It gives it a nice texture; however, being that we are compressing images to a significantly smaller size, and removing the noise makes the image much easier to compress, we will be using it today. First, set your delta. This is a certain frequency used to detect noise. The lower, the less will be removed, and the higher, more will be removed, but less detail will be preserved. Blurring with the highest possible maximum delta is the same as a normal Gaussian Blur. I will have it set relatively low, but high-enough to smooth over some of the grain. I am using an Apple iPod Touch 4th generation camera, and in my experience, a maximum delta of 10-25 seems to do the trick. Again, the lower it is, the more detail will be preserved. Now set the blur radius. This is how much the grain of the frequency you set will be blurred. A very low blur radius will generally not remove the noise, but rather soften it, which I believe creates a very ugly effect. I have it set to 3, which will blur it three pixels, enough to remove a bit of it. Here is what my image looks like so far. Now we’re going to zoom-in.

Use the selector tool to cut out any unnecessary portions of image. We are doing this because we will be shrinking it down to a lower resolution, and the more we zoom in, the more detail will be preserved once we do shrink it. If you need to, open up Calculator to make sure your aspect ratio is correct. In this case, I made sure it was a perfect 1.333:1 (4:3). Depending on the aspect ratio of your image, this will differ. Another common aspect ratio is 1.78:1 (16:9)  Here is my image now. Now, we’re going to use the shrink tool to downscale it to a lower resolution. I will be using 640×480, which I believe is the perfect resolution for 4:3 web images. If you are making a 1.78:1 image, you may want to shrink it down to 640×360 or 853×480. However, depending on your needs, you may wish to make it even smaller. As an example, I will be using 320×240, a relatively low resolution. This will show much less detail, but it will have a significantly smaller file-size. Here is the 480p version and here is the 240p version.

Now we’re going to run yet another (very minor) round of noise reduction. This will, again, smooth over some of the grain and make it easier to compress. If you scaled your image to a very low resolution such as 320×240, this may not even be necessary.

Now we’re going to save our image as a .jpg. Unfortunately, here is where you will probably have to make the biggest sacrifice. JPEG compression can make the file size MUCH lower, but with a bad effect upon the image quality. You have to balance these two things. When it is asking you your settings, make sure you have “Show preview in image window” checked. This will allow you to preview it before exporting. Then, lower and raise the quality setting, while paying attention to file size. At each setting, unclick “Show preview in image window.” This will revert it to what it would look like as a lossless .png, so you can easily see how much you’re losing. I finally settled upon a level 90 JPEG, which will have a file size of only 55kB. That’s pretty astounding when you consider that the original image was 280kB, and even more so when you look at the size of a lossless .png or an uncompressed image. So now, finally, here is my image. Thanks for reading!