1.2 Creating and using the layer opacity masks

PhotoFlow Wiki > User Manual > Creating and using the layer opacity masks

The majority of the tools in PhotoFlow can be associated with opacity masks, that allow to locally control the strength of the alpha blending between the tool output and its input.

When the mask has a value of 1.0, the tool output completely replaces the input. On the contrary, when the mask is 0.0 the tool output has no effect, and the blend output exactly matches the layer input. For mask values between 0.0 and 1.0, a simple linear formula is used:

blend_output = mask * layer_output + (1.0 - mask) * layer_input