Image Processing

Pixelization

Pixelization is used to render certain areas of an image unrecognisable. The yellow cloud can apply pixelization directly to images you intend to publish. To configure it you’ll need to adjust one parameter, but also upload a mask that defines the areas to be pixelized.

The factor determines how much individual pixels are being blown up. Note that the exact effect will vary depending on the resolution of your input image. Larger images may require a larger factor than smaller images.

The other thing the pixelization requires is a mask, which you can upload from your computer with the provided controls, but you will have to create it yourself. A mask is an image that defines in which areas the pixelization should be applied. Expected is a jpg image with a black background, in which the areas you wish to be pixelized are marked in white. Here is a short tutorial on how to make such a mask using GIMP, a free image editing program. You may of course use whatever image editing program you prefer to create the image.

How to make a pixelization mask (with GIMP)

First off it’s a good idea to download an image from the table you want to pixelize. While the pixelization mask does not need to match the resolution of the source image, it is the most convenient way to create the mask on top of the image you want to pixelize. Once you’ve opened the image in GIMP, here’s what you do:

Create a new layer:

In the layers dialogue, click on the left-most icon in the bottom. Enter some name for the layer, and click OK.

In case you don’t see the layers dialogue, you can bring it up by pressing ctrl-L, or by going through the top menu: Windows → Dockable Dialogues → Layers.

Mark the pixelizazion area:

Activate one of the three selection tools in the toolbox. There’s rectangles, elipses, and free polygons. I’m going to use the polygon for this tutorial. If you don’t see the toolbox anywhere, you can bring it up by pressing ctrl-B or from the top menu, going through Windows → New Toolbox.

Now mark out the area you want to pixelize with the selection tool of your choice. Make sure the layer you created is selected (it should be if you didn’t do anything else in the meantime)! In case of the polygon tool, we can just create arbitrary points to encircle the desired area. To close the polygon just connect back to the first point.

You can select multiple areas at once using the control key if you need to.

Color the mask:

In the toolbox, select the bucket fill tool. Also make sure that your foreground color is set to white. If it isn’t, change it.

With the bucket tool selected, just click inside the area you wish to pixelize. The result should look something like this:

Almost done, now we merely need to turn everything else black. Click on the lowest layer to select it, and make sure your background color is set to black:

Then just press ctrl-A to select the entire background layer, and hit the delete key. voila:

Export your mask and upload it to the yellow portal:

In the top menu, go to file → Export as:

In the menu that pops up, enter a filename (with a .jpg extension), and click export. Another menu with JPG options will pop up. You can put the quality a decent way down, we don’t need it here. Also uncheck all checkboxes except the lowest one, then click Export:

All that’s left now to make your pixelization work is to go back to the yellow portal, click the “choose” button in the upload widget, select the file you just created, then click on upload. And finally, of course, save your table configuration. The next image coming in should already have the pixelisation applied.

Should you ever need to change the mask, you can upload another one at any time. This will simply overwrite the mask that was used for this image.