The biggest problem with the above approach is that the shine of the light does not interact in any way with our base footage and thus appears to be stuck on top of it. One way to improve this would be to create many small masks on the FireShine layer to light up highlighted areas like face, arms, fingers, table and other elements that would be affected in real life by a light source at that position. However, there is a much simpler way: using a matte layer for the light.A matte is a layer that is used to define the transparency of the layer directly below it. By creating a matte based on our footage and applying it to the shine of the fire, we can tie the lighting effect and the footage together organically
Duplicate the 'Footage Comp' layer and place the copy above our FireShine layer. Rename the layer to 'Light Matte'.
Notice that the new layer will hide the FireShine layer, but that is ok - we just want to be able to see the Light Matte while we make adjustments. Once we are happy with our matte, we will hide it and apply it to the FireShine layer.
We want to use the brightness of the footage to define how strongly the light shine will affect it. Bright areas will receive a lot of shine, dark areas will receive very little. Now I know that this is not how it works in reality, but we just want to blend the FireShine layer more organically into our footage. Additionally, keeping the dark areas dark will retain shadows and thus enhance the feeling of a real light source being present in the scene.Now let's get to adjusting our matte so we can use it
Apply a hue/saturation effect to the Light Matte and fully desaturate the image. Now, add a brightness/contrast effect and increase brightness and contrast to bring out the bright and dark areas of the footage. Since the footage is a little grainy and fire glow is usually fairly soft, I have also added a fast blur effect to the matte to smoothen it all out a little bit. These are the effects on the Light Matte layer:
Your Light Matte (with the FireComp layer still visible on top of it) should now look so something like this:
Now all that is left to do is to apply our Light Matte to the FireShine layer!To do this, turn off the visibility of the Light Matte layer. Select your FireShine layer and set the track matte from None to Luma. 'Luma' means brightness and indicates that the alpha for our FireShine layer will be taken from the brightness of the layer directly above it, which is our Light Matte layer.
So wherever our Light Matte layer is black, the transparency of the FireShine layer will be 0%. Wherever the Light Matte is white, the FireShine layer will be fully opaque. Gray levels specify different levels of semi-transparency
You can quickly check how our FireShine layer looks now by settings its blending mode back to 'Normal'. I also turned off the FireComp layer to show only the FireShine affected by the Light Matte:
Now, this more sophisticated FireShine layer can be applied to our scene by setting its blending mode to 'additive'! The final scene looks like this:
Voila, the candle light suddenly sits a lot more organically on your footage as the affected areas are literally defined by the footage While this may not be the most realistic way, it is fast and easy to do and does look a whole lot better than simply 'adding' a light layer over your shot!Happy lighting!