| That’s a really cool tutorial, it’s basically the same way I’ve been doing glows except it never occurred to me to stack them all up on the one layer. Thanks for the link.
However two things spring to mind. Firstly, I make things glow A LOT and I usually find that different colours need different blur settings IF you want them to look the same. Linking all the blurs for the same layer with an expression is clever and a great starting point, but I think that if you had elements that were all unique colours, you might want to manually adjust some of the numbers if you want the glow to look the same on them all.
Secondly - and I really don’t know, just thinking out loud - while multiple layers with different blur settings is undoubtedly more accurate and better looking than the default AE glow, I’m still not sure that it’s a true inverse square because the blur profile itself is gaussian. So you are stacking up multiple bell-curves on top of each other. Sure it looks good but I don’t think it’s 100% mathematically perfect.
-Chris
Here is a great Ae tutorial about building your own glow preset based on inverse square law:
Cheers, Mathias
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If you want to do it mathematically then it’s more complex than you think, as you need to consider the gamma of the workspace you’re using.
Making something glow by stacking up multiple layers with different blurs is faking it, but probably the best way to do it in 8 or 16 bit modes. It’s the way i do it too, although I use the screen mode (not add), and I usually have a desaturated layer near the top set to classic colour dodge to adjust the “hotness”. From a mathematical perspective, you’re not just looking at the blur profile but also the gamma of the workspace so this multiple layer approach is going to be difficult to calculate.
The alternative approach is to comp in 32 bit linear mode, where you don’t need to stack up multiple layers. You just have your source layer and make the colour super hot. Then you blur it and the blur naturally spreads out the light. The falloff will depend on the type of blur you use. I did ask a while ago (for exactly the same reason as you) if there’s a blur with an adjustable profile including inverse square, which would be very useful for comping glows in 32 bit float mode. I can’t remember the answer, but there’s something for you to look at.
So basically - multiple layers using add/screen and blur is an 8/16 bit fudge for a gamma working space like sRGB/HDR. A single, super hot layer with a single blur in 32 bit linear float is the more natural approach.
Or you can just use a plugin that does it, as lloyd suggests :-)
-Chris
So, if I were applying that to say, the blur of a layer, what would be the "distance" variable? I'm stacking several layers with Add transfer modes and variable amounts of blur. The inverse square law states that intensity is inversely proportional to the square of the distance from the source. Symbolically: intensity = 1 / (distance^2)
Doing a little math, when the distance is 1, the intensity is 1. When the distance is 2, the intensity is 0.25. When the distance is 3, the intensity is 0.111. When the distance is 4, the intensity is 0.0625.
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