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I am wanting to animate a row of LED lights. I have separated the LED lights from the rest of my object with the pass index/ID mask functions; currently all of my LED lights are on pass index #1.

What I want is to have a minor halo effect around the lights, but only when they are active. Currently, when I add a halo effect to my pass index #1, all of the LED lights have a halo effect regardless if the LEDs are emitting light. All LEDs are diffuse and emission shaders, so I can animate by controlling the mix amount between diffuse and emission.

Is there any simple way to have the halo effect created through recognizing light emission values, or will I have to just animate each LED as its own layer of compositing?

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    $\begingroup$ Have you tried the Filter > Glare node instead? It works based on per pixel light intensity $\endgroup$ – Duarte Farrajota Ramos Jun 4 '16 at 20:34
  • $\begingroup$ I had tried that as well, but it wasn't working. Is it based off of theshold levels? $\endgroup$ – hallu Jun 4 '16 at 20:55
  • $\begingroup$ Since it is not listed in the manual I am unsure how to use it :/ $\endgroup$ – hallu Jun 4 '16 at 21:14
  • $\begingroup$ Cegaton answered most of my questions, but I was running into another issue as well. I had set the glare node to work off of an object mask ID, so rather than reading the render's per-pixel light emission it was simply applying a glare effect evenly across all LEDs in the mask ID. $\endgroup$ – hallu Jun 4 '16 at 21:41
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With the glare node you can control the threshold at which the effect kicks in.

In this example a the cubes have different emission values. Form left to right they double in intensity.

Using the threshold control on the Glare node you can determine at what point the effect starts:

enter image description here

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How would you know which values to use? You can see the values for the rendered image if you left click and drag the mouse over the image. You'll see some values at the bottom of the screen On the left side you'll see values for RGB (red, green and blue).

enter image description here

enter image description here

Those values are the scene referred values before any color transformation. Konwing those values you should be able to determine the value for the glare threshold.

Update for 2.8:

To show the sampler in the Image Editor window press the right mouse button. The sampler window will appear at the bottom of the screen.

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  • $\begingroup$ Perfect! The glare node isn't in the manual, so my adjustments to the threshold weren't showing anything. Out of curiosity, what is the far right cube set at for emission level? $\endgroup$ – hallu Jun 4 '16 at 21:24
  • $\begingroup$ Oops I closed the project... but read the edited answer. $\endgroup$ – cegaton Jun 4 '16 at 21:43
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    $\begingroup$ For testing purposes you can also set Mix value of Glare node to 1 which will mean using processed (glared) image only; thus you'll see what Glare affects. $\endgroup$ – Mr Zak Jun 4 '16 at 21:57

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