Image Editor

What is an Image Editor?

An image editor is a type of application capable of editing digital images. Since digital images can be all sorts of graphics, including drawings, logos, and photos, an image editor is generally also a graphic design tool, a digital art application, or a photo editing software. Note that each one of these sub-types of software may have features that the others do not possess.

Notable Features

Canvas: the area where the image is displayed in an image editor is generally called the "canvas."

Layers: most modern image editors support a system of a "layers" functionality. In this function, a single image is composed of multiple "layers," and each layer can be edited individually. Layers may have transparent pixels, in which case the pixels of the layer below is displayed instead. In most cases, layers also have a blending mode, which configures how one layer is blended with the layers below. Applications that have layers will provide methods to "merge" the existing layers or "flatten" the image by merging everything. You'll also typically find ways to "copy" the image of the merged canvas instead of copying only pixels from the current layer, and ways to "sample" (e.g. with an eyedropper tool) the color current layer or the combined color of all visible layers.

Formats: there have been countless image formats created since the dawn of computer graphics. Different image editors are capable of opening images in different formats. They generally support the common formats PNG, JPG, BMP, GIF, and in some cases, WebP. None of these formats support layers, which means every image editor comes with its own image format for its own project files, such as Photoshop's .psd, GIMP's .xfc, Krita's .kra, and so on. Consequently, they also need to have the ability to "export" images from their own format to a common format such as PNG and JPG that will be supported to other applications. It's worth noting that the ability to open an image in a format is called decoding, and requires a program called a decoder, while the opposite is called encoding and requires an encoder. Sometimes, an application can decode a format but it can't encode to that format, e.g. it may be able to import a PSD file, but not be able to export a PSD file.

Painting Tools & Filters: image editors are mainly capable of two operations: creating "new" pixels by using drawing tools such as a paint brush, or a line tool, or a shape, and modifying the current pixels with "filters" such as blur, and changing the hue, or brightness and contrast.

Toolbox-Based Workflow: in general, image editors will have a toolbox with various tools you can click to activate. Only one tool may be active at a time. When you click on the canvas, what effect clicking has varies according to the currently selected tool. In most cases, the tool will have advanced options that can be configured in some toolbar or panel, which means the toolbar or panel also changes according to what tool is currently active.

Selection: by default, operations done in an image editor apply to the whole image, but it's generally possible to select parts of the canvas to restrict where operations are applied. While pixels are selected, you'll see an "ant-line" effect on the pixels. Many common operations exist for this selection, such as deselecting it, inverting the selection, growing the selection, and, in some application, "feathering" the selection, which makes its edges fade.

Notable Features of Sub-Types

Not every image editor has every possible feature, as they purpose may vary a lot. Some notable features you'll find in certain types of editors:

For graphic design: you'll at least find the ability to display "rulers" on the canvas. Clicking and dragging from these rules will create "guides" on the canvas, which are lines across the canvas that aren't exported, which will help you align elements on the canvas. In some cases, drawings tools will snap to these guides. Similarly, you may find the ability to display a grid on the canvas, and tools to add text to the image.

For printing: you may be able to change the unit of distance from pixels to millimeters or inches. Some applications support CMYK color, which is used in printing, instead of RGB color as well.

For photo editing: you'll find better tools to select areas of the image, at least a better magic wand, since a lot of time is spent selecting a subject or object on the photo to change an aspect of it, and you'll most likely have the ability to work with linear or perceptual color spaces, instead of gamma corrected RGB, which is what most image editors work with. It's worth noting that a side effect of this, is that applications for photo editing sometimes yield issues with images that aren't photos. For example, if you export a transparent PNG from Inkscape and import it in GIMP as a layer, with white in the background, it won't look the same way as it did in Inkscape, because since version 2.10, GIMP doesn't do blending in gamma corrected spaces anymore, while Inkscape does, so a semi-transparent pixel in Inkscape blends different from how a semi-transparent pixel blends in GIMP by default. You'll also find more advanced filters to handle colors and lights in photo editing applications, and tools to easily remove parts of an image, e.g. to remove a boat from the sea, leaving only the sea.

For digital art: digital illustrators generally work with drawing tablets, which is like a pen you put on a small rectangular surface. This pen gives the computer more information than the mouse does: it can tell programs how much pressure is put on the pen, and what angle the pen is tilted toward. Image editors with focus on digital illustration will support pen pressure, and they will have complex brush engines to create all sorts of digital artwork based on traditional media: pencil drawings, watercolor, oil painting, etc. In some cases, you'll also find the ability to create animations, although in this case, we're mainly talking about very, very short animations, of around a few seconds long. For longer animations, you a specialized tool for animation, like OpenToonz. In any case, it may include onion skinning, and if it has a timeline based animation editor, keyframes (see FireAlpaca for a tool that supports animation without a timeline). Some digital illustration software, like Clip Studio Paint and Paint Tool SAI, also have the ability to create "vector" layers for line art specifically. These layers aren't raster image layers: they don't contain pixel data, only line, curve, and pressure data. Another common feature is the ability to enable a symmetry mode, that automatically mirrors every stroke drawn on one side of the canvas to the other side.

For pixel art: it's worth noting that there is another, more specific category of digital art applications specifically made to create pixel art. These are technically also image editors, but one key difference of them is that they work mainly with images that have a limited number of colors. In the past, all computers worked with a limited amount of colors because it simply wasn't possible to display more than 2, or 16, or 256 colors on the screen. As time went on, we became able to display more colors on the screen, and so all the tools that existed in old image editors to manage a small number of colors stopped making sense. We didn't need them anymore. However, there are many games that prefer the "retro" aesthetic, or even pixel art as an art form itself, and for that, they need tools like palette management that aren't found in the typical image editor. Examples of such editors include GraphicsGale, Aseprite, and mtPaint.

For other digital graphics: it's worth noting that there are other uses of digital images besides the ones above. If you're working with game development, 3D modelling, or even some more niche software, you may need to use images in ways that aren't normally used. For example, to create a bump map for a 3D texture, or to create a PNG with transparent colored pixels because something uses the alpha channel for some purpose besides transparency. In these situations where you want to create graphical effects, you don't want to edit "images" anymore, in the sense of changing things you see, you want to edit pixels, the graphical data itself. These things are also possible with image editors. A simple example is that you can take a black and white image and make the black become transparent by making the alpha channel the exact same thing as the red color. This act makes absolutely no sense for photo editing or for digital art, but it's something you may want to do if you have a black and white image, and that's completely possible. Similarly, if the areas you want opaque are white instead of black, you may need to "invert" the pixels. Inverting the color of the pixels is an operation that makes no sense as well, but most image editors support it, and from time to time you even see it used as a graphical effect.