“The fancy software figures it out for you.”

I want to tell you about something that might seem oddly specific and perhaps too technical, but a) at the end of it you will have a useful phrase somewhere in your brain that will pay off one day, and b) I swear I will make it worth your while. Have you ever seen this problem? The screenshot on the left is fine. But there is something wrong with the one on the right. In light mode, the shadow is wispy and weird. In dark mode, things are even stranger, and the shadow is almost… a glow? I stumbled upon this problem occasionally for years now – there are a few screenshots on the blog with this weird problem, even – but it was never feeling like a deal breaker. However, I finally sat down to figure it out today. Turns out, there are two kinds of approaches to alpha channel/​transparency. The normal one we all know well is called “straight alpha.” But on the right, we were looking at “premultiplied alpha” – something entirely more complicated, where the background is baked into…