Really, this makes me so confused. What’s the difference between this formula and the previous one? They both multiplied A and B with its own alpha right?
rohta
I think it allows us to separate out alpha as a fourth component of "color" like we normally do instead of just looking at RGB values, but I might be wrong.
JimL
@VegitableChicken @rohta I think it is totally different. The C and C' value are the same! But C' have the alpha value applied and C have not. For C', the origin (without alpha) color should be C'/a'c. This problem is stated in slide 37.
Ace
Can you elaborate on why premultiplied alpha is correct and the other one fails?
jasonx
The composite alpha equation is here is equivalent to "screen blend" https://en.wikipedia.org/wiki/Blend_modes#Screen where C_alpha = 1 - (1 - A_alpha) * (1 - B_alpha)
RyuK
@VegitableChicken I guess the main idea of premultiplied alpha its to save computation.
weiyuc
I think this also help when you have multiple objects. Even if you combining first two objects without the pre-multiplied method, the combined result is still a pre-multiplied one, so you should combine the next object with pre-multiplied method.
Really, this makes me so confused. What’s the difference between this formula and the previous one? They both multiplied A and B with its own alpha right?
I think it allows us to separate out alpha as a fourth component of "color" like we normally do instead of just looking at RGB values, but I might be wrong.
@VegitableChicken @rohta I think it is totally different. The C and C' value are the same! But C' have the alpha value applied and C have not. For C', the origin (without alpha) color should be C'/a'c. This problem is stated in slide 37.
Can you elaborate on why premultiplied alpha is correct and the other one fails?
The composite alpha equation is here is equivalent to "screen blend" https://en.wikipedia.org/wiki/Blend_modes#Screen where C_alpha = 1 - (1 - A_alpha) * (1 - B_alpha)
@VegitableChicken I guess the main idea of premultiplied alpha its to save computation.
I think this also help when you have multiple objects. Even if you combining first two objects without the pre-multiplied method, the combined result is still a pre-multiplied one, so you should combine the next object with pre-multiplied method.