What is the formula for extracting the src from a calculated blendmode?

问题

How does one go about using a alpha blending formula to achieve the src rgb color from the resultant of the 2 blended together

回答1:

Well, you can just reorder the alpha blending equation

Value = (1 − α) · Value₀ + α · Value₁

However, there are four variables in that equation: α, Value, Value₀ and Value₁. You need to know three of them to calculate the fourth. So in your case you know the resulting color, Value, the α and maybe Value₀. You can then reorder the equation as follows:

−α · Value₁ = (1 − α) · Value₀ − Value

Value₁ = (−1/α) · ((1 − α) · Value₀ − Value)

That is, if I understood you correctly. Which might not be the case. You might want to clarify your question.

来源：https://stackoverflow.com/questions/2139350/what-is-the-formula-for-extracting-the-src-from-a-calculated-blendmode