GIMP is a fine alternative to Adobe Photoshop, but it does have its limitations. For one, it does not always allow you to add an alpha channel to your artwork. During those moments, you need another way to modify the background as you can do with other applications.
There are several ways to get around the lack of an alpha channel option in GIMP. You can add a transparent layer. Otherwise, you can manually add an alpha channel. Bother methods have their benefits and downsides.
Once you have an alpha channel, you gain access to some advanced GIMP editing techniques. By reading further, you will learn what these techniques are and how to use them to enhance your artwork.
How to Add an Alpha Channel in GIMP
Color digital images display color through a three-channel color space such as the red, green, and blue channels of an RGB image. While these channels are defined by color, they are black and white images containing the color intensity of the particular channel. You only get a single-color image after your computer sends the image to the display.
Most of the time, those three channels are all your computer needs, but you are not limited to them. You can add other channels to gain more control over the display such as numerous alpha channels.
Graphics applications such as GIMP use alpha channels to set and track opacity and transparency. Each layer of an image can have an alpha channel, letting the layers underneath shine through.
Adding Alpha Channels in GIMP
Unlike other graphics applications, GIMP does not add alpha channels automatically. Instead, it just recolors deleted pixels with the current background color. This is because the application has no way of detecting if alpha channels already exist, and just presumes they do. Since the GIMP developers do not see value in such a feature, this situation is unlikely to change any time soon.
As such, you must manually add the channel. Luckily, you have several ways to do that depending on your version of GIMP. These methods include:
- Select the “Layer → Transparency → Add alpha Channel” menu option
- On the appropriate layer, Right-click the Layers palette at the bottom right of the screen and select “Add Alpha Channel”
- Create a new layer (requires GIMP version 2.20 or later), or select the “Transparent” option in the “New Layer” dialog box
- Select the “Color to Alpha” option from the “Layers → Transparency” menu to make any pixels of the selected color transparent
Either method should work. So, you must choose the best one for your workflow. Once added, you can modify your image’s transparency as much as you want.
Check for Existing Alpha Channels if Nothing WOrks
If none of the above methods work or the options are not available, then your image might already have alpha channels. GIMP will not let you override existing channels. As such, this should be your first troubleshooting priority.
Your image may contain preexisting alpha channels for numerous reasons. The file may be a working file from another graphics application that left the alpha channel information in lace. Otherwise, GIMP might have automatically added them without telling you since it detected the image already has multiple layers. The list can go on, but the result would be the same regardless of the reason,
Fortunately, you can easily check to see if your image file already contains an alpha channel from the Channels panel. Normally, GIMP places it next to the Layers panel unless you changed it. It usually just sits behind the other panels and the main canvas. You can easily move the panel foreground by clicking the Channels label.
The Channel Panel displays every channel present in the current image layer. These channels will be based on the current space such as Red, Greem, and Blue for RGB, or Hue, Saturation, and Brightness for HSB images. If present, the panel will also list any alpha channel.
Adjust the Opacity of a Layer if Nothing Works
If no method works, and you know your image does not have alpha channels, you can still simulate the function on an alpha channel by adjusting a layer’s opacity levels. This is not ideal as this “ghost layer” can make the entire image transparent if you are not careful.
To make things simple, the GIMP does not automatically add an alpha channel. It will even block your manual efforts in some cases as well. Fortunately, there are a few fixes to the problem including checking for the presence of existing alpha channels and making transparent layers. If all else fails, you can just use pre-rendered assets from Placeit.net and similar services.