What Is the Alpha Channel in PNG Images?

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If you have come across the term alpha channel and are wondering what it refers to, let’s find out.

The alpha channel allows for transparency in an image. Not all image formats support it, but PNG is one of the most commonly used image formats that does.

In images with an alpha channel, each pixel not only has a color value, but also has a numerical transparency value that defines what will happen when the pixel is placed over another pixel.

A pixel with an alpha channel value of 100% is completely opaque. It becomes increasingly transparent as the value moves toward 0%. At 0% value, the pixel is fully transparent.

Speaking in more visual terms, think of an alpha channel as a mask you’re putting on an image. Now you erase portions of the mask based on the portions of the image that you want to allow to show through. As expected, the pixels that allow you to see through the image are at 0% opacity. They’re as good as invisible.

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Now, the question is how is the alpha channel information useful to you. It’s handy if you want to retain the transparency in any portion of an image, and for that you’ll need to use an image format that supports and stores the alpha channel information. As a general rule of thumb, it’s best to opt for the PNG format if you want to retain transparency information.

If you have trouble deciding when you should be using JPEG, GIF, or PNG for your images, take a look at this image filetype guide that we have published.

Have you lost important image information because you didn’t save it in the right format? Were you able to recover it? If yes, tell us how in the comments.

Image Credit: Abstract transparent cubes by iABC via Shutterstock

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