GIMP 2.10.32
If you want to work with image processing, GIMP should be your first port of call.
GIMP is the go-to tool for most Linux users when they’re working with bitmap graphics – and with good reason. It’s a highly capable tool in many different areas of image editing and creation.
In the past, the user interface came in for criticism, but that judgment feels a little unfair, given what it has looked like for the past few years. It now defaults to a singlewindow interface, with various toolbars and panels around the sides of the main area.
There is simply no way of offering such a huge range of features without a somewhat complex interface.
GIMP is a destructive editor. In other words, you alter the bitmap as you work on it. However, it’s possible to add an element of non-destructive editing by using layers. For a simple example: load an image into GIMP and add an empty layer by clicking on the + icon in the Layers panel. This gives you a blank, transparent layer to work on. From here on, you can do anything you want to that layer without affecting the original bitmap below.
You can even carry out functions that require interaction between the layers. For example, if you want to use the Clone tool to remove a blemish from a photograph, you can while using layers. We’ll assume you have a photograph loaded and you’ve created a blank layer on top of it. Select the Clone tool from the main toolbox. Select the layer that the photograph sits on and Ctrl+click the area with a blemish. Then select the blank layer and left-click to apply the cloning operation on top of it. It’s just an extra couple of clicks, but this means you can revert to the unaltered image at any stage or switch the layer off (Eye icon, Layers panel) to compare with the original.
Working like this means that you can change your mind and remove a set of alterations at any stage. As the memory cost of creating these layers is negligible, you should create a new layer every time you arrive at a decision point. Create a new layer from the visible screen (Layer > New From Visible) for operations on the full image, such as filters.