: What does 'alpha' mean in design software? I've never done any graphic art or design. So I have a super basic question. I'm learning to use Krita. I keep seeing the word "Alpha", what does

@Sent7350415

The "alpha channel" is the opacity of the pixel (0% transparent, 100% opaque, intermediate values are possible). So, instead of being characterized by three channels (RGB, for instance), pixels are denoted by 4 (RGBA). So (100%,100%,100%,100%) is an opaque white pixel while (100%,100%,100%,0%) is a transparent white pixel (that looks exactly the same as a (0%,0%,0%,0%) transparent back pixel, until you start playing with the alpha channel.

You can often edit the alpha channel directly using a layer mask.

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@Vandalay110

'Alpha' is the opacity channel. Each layer can have such a channel, governing how transparent or opaque every pixel on the layer is.

Such a channel is essentially a greyscale image of exactly the same dimensions as the layer. Every pixel on the alpha channel corresponds to the same pixel on the layer. The colour of a pixel on the alpha channels affects the opacity of the corresponding pixel on the layer.

Usually, 100% black means 100% transparent (and thus invisible) and 100% white means completely opaque (or 0% transparent). Any percentage of grey is an intermediate opacity.

This way, an alpha channel allows you to control each pixel's opacity separately.

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@Cugini998

Alpha channel means the opacity of an individual pixel. This allows you to layer pictures on top of each other neatly as each pixel knows how much it should contribute to the compound image.

The name alpha to my understanding derives form the formulas used for blending which predate alpha channels, these used alpha character in them to parameterise the amount of blending (as to why that is I dont know, probably arbitrary choice). Thus if you wanted to drive each pixel with a separate blend value you needed a source for this alpha value. Thus calling the driving source an alpha channel is pretty logical, and straightfoward extension.

Side note: From the fact that you have 4 channel follows that there is no such thing as a transparent pixel. As even a fully invisible pixel has a color, and this can come and haunt you when you do image scaling or other operations on them.

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