Colour 302 : Quick guide to Opacity, Alpha and Luma.

Alpha

• Alpha controls transparency for each pixel in an image.

• It’s stored in a separate channel (alpha channel) and allows for detailed transparency effects like soft edges or cutouts.

• Used in PNG images, compositing, and masking to control how much of a layer is visible.

Opacity

• Opacity controls how see-through a layer is. Higher opacity means less transparency.

• Unlike alpha, which affects individual pixels, opacity applies to the whole layer unless masked.

• Used in digital software to adjust how much of a layer is visible in blending.

  Opacity vs. Transparency

• 100% opacity = 0% transparency (fully visible layer).

• 0% opacity = 100% transparency (completely invisible).

• 50% opacity = 50% transparency (semi-transparent layer).

Unlike alpha, which varies per pixel, opacity affects the whole layer evenly unless a mask or gradient is applied.

Luma

• Luma is about brightness, not transparency. It measures how bright a pixel is based on grayscale values.

• It’s often used for luminance-based masking or effects where brightness determines visibility.

• Used in luma keying (e.g., removing backgrounds based on brightness) and grayscale-based effects.

Key Differences

• Alpha is a dedicated transparency channel.

• Opacity is the opposite of transparency and controls how visible the entire layer is.

• Luma is based on brightness and doesn’t store transparency directly.