First of all I want to apologize for any english mistake I'll make.
Then, here is the question. I'm very new to AE and Graphic is not my first job, I do that as an hobby and to help me and some of my colleagues with film scoring.
I would like to know if there is a way for a footage to act as a light emitter. To be more precise I have a flame footage, inside a cave (2 separate footages ofc). I would like to know if there is any way to make the flame layer glow that yellowish/orange light and illuminate the Cave footage.
Let's hope you know how to work masks. Firsly, you can make a solid similar to the color of fire and use that as your light around the cage, so just mask it out around varioud parts of the cave, prrhaps duplicate the solid and do it over the footage in varioud places. Then, mask out your fire and use the standard glow from AE. I think that covers a general overview of your effect?...
"It's all around us Neo, temporary constructs of time....."
There are 2 separate issues here. First is the glow for the fire footage. You should work in 16 or 32 bit color depth for your AE projects. This will enable you to get smooth soft glows. You can use AE's own Glow effect applied to the fire and maybe a second pass on an Adjustment layer on top of all the layers to help blend in the effect. You can assign colors for the glow to have the orange reddish cast you want.
Second - the light on the cave walls. It would have been best to shoot this with a practical effect (like light generated from a real flame or flashlights) to get the shadows. However, there are several ways of complexity you can work towards. The easiest would be to create a vignette type of color grading around the fire (to give the orange red cast), making sure you animate the intensity of the brightness of the cave and the size of the vignette to match the flicker of the flame. Next step would be to create a series of garbage masks to adjust major features- actors, big objects and large rock face features. This should be used to highlight where the light hits and create shadows where the light casts them. For more detail add more masks for the smaller features (contour of face features, modeling on objects details...). One more Adjustment layer with an overall color correction, pushing the lighter areas to orange and the dark to a dark bluish gray should add to the overall effect.