If you’ve spent any time at all on social media lately, you’ve probably seen pictures that used a grid of colored blocks to obscure part of the image.
Sometimes it’s personal information in a screenshot, sometimes it’s a person’s face in a photo, but they’re all created in a similar way: some of the underlying pixels are averaged and expanded, discarding the details that help your brain to see a coherent image on-screen.
The Quick Guide to Pixelate an Image in GIMP
Pixelating an image in GIMP is pretty simple, once you know where to find the right filter.
- Step 1: Open the Filters menu, select the Blur submenu, and choose Pixelize.
- Step 2: Customize the Block width setting until your image is obscured and click OK.
That’s all there is to it! If you only want to pixelize a small part of your image, you can create a selection before applying the Pixelize filter.
If you want to explore all the settings options, read on! I’ll also explain the danger of using pixelation effects to hide your personal data, and show you a way to use the filter to create some cool artistic effects.
Protecting Your Personal Info
A lot of people use pixelation to hide their personal information when sharing screenshots or other images online – but it’s not always as safe as it seems. Even though a human viewer probably won’t be able to see past the pixelation, a sophisticated computer program might be able to.
Because the algorithms used to pixelate your image data are open source and available to everyone, it’s sometimes possible for a “de-pixelize” filter to make an educated guess about how to unscramble a pixelated image.
It’s not possible in every situation, because if enough image data is missing, it’s impossible to re-create the original (which is partly why you can’t just ‘enhance’ a blurry video to make it clearer, despite what low-budget TV crime dramas would have us believe).
But if the pixelation is not done properly, you risk leaving your information unprotected.
If you absolutely have to share an image online that contains areas you want to hide, it’s safest to simply use a solid block of color to cover up any sections you want to stay private – no algorithm can overcome that. But really, to be safe, you’re probably better off just not sharing it at all.
Enough serious stuff, let’s get back to pixelating images in GIMP!
The Detailed Guide to Pixelate an Image in GIMP
Time for a closer look at how the Pixelize filter works in GIMP.
Step 1: Locating The Pixelize Filter
To find the Pixelize filter, open the Filters menu, select the Blur submenu, and click Pixelize. It might seem strange to you that it would be categorized alongside Gaussian Blur and other filters that create soft-edged blur effects, but they actually share a very similar purpose: hiding detail.
Step 2: Configuring The Pixelize Filter
GIMP will open the Pixelize filter dialog box, shown below.
The most important settings are Block width and Block height, which are locked together by default in order to maintain a square aspect ratio.
These settings control the size of your ‘pixels’ in the final output, and they make all the difference between creating a low-resolution effect and actually hiding your source image.
The default setting is 16, but reducing the size even further to 10 creates a pixelated effect without hiding the actual image contents too much (see below).
But by the time you get up to a block size of 30 or so, your original image is pretty blurry and hard to make out. If you didn’t already know it was Wilber in the image below, would you be able to recognize him?
Most of the time, you’ll want to leave the Shape setting to Square. Pixels are square, so this creates the standard blocky effect that you’re probably trying to recreate. However, if you switch to the Round setting, you’ll see something closer to a half-tone dot pattern used in printing.
The default settings use your currently selected background color to fill in the gaps, but you can set this to transparent by clicking the color swatch, locating the A slider (representing alpha channel transparency), and setting it to 0.
This also works with the other shape types as well. Just remember to set the background color to transparent, or GIMP will fill the rest of the layer with your chosen background color which can spoil the effect.
A Final Word About Pixelating Images
Now that you know how to pixelate an image in GIMP, remember that it’s all done with math – and what one computer can encode, another computer can decode – so you might want to choose a better way to obscure your personal information online.
Even something as simple as a solid block of color can be more effective, as long as your image doesn’t store the color blocks on a separate layer that could be removed.About Thomas Boldt