From the September 2014 issue

Using masks, part 1

Astroimager Adam Block reveals an advanced image-processing technique: masks.
By | Published: September 29, 2014 | Last updated on May 18, 2023

When I talk about an unfamiliar processing construct such as a mask, I ask people to consider the simplest element of an image — a pixel. A pixel has two attributes: color (chrominance) and brightness (luminance). However, in Photoshop, pixels have an additional attribute called opacity, which determines the visibility of the pixel and how easily you can see a pixel in an underlying layer. Grayscale images called masks manage the opacity of a pixel.

Every pixel has an associated percentage that defines its opacity. A 100 percent opacity means the pixel is fully visible and a 0 percent opacity means it is invisible.

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