AO for specific area or objects, and TV flicker questions

Hi, does anyone know if there is some possiblity to get AO pass in a scene only for specific area or between 2 specific objects?

I’m missing some contact shadows between some object in an image sequence I would like to add a shadow only between specific objects for example between the chips bag and the jeans and between the feets and the sofa in the image.

I was using until now a negative spot light between the bag, but I’m not sure if it’s the best way, it makes the render slower and more noise probably…

I thought also just to create a new render layer and to make a special light source for it, and then to render out just the shadow, but I thought maybe there is a nicer way to get this AO, maybe some magic node :slight_smile:


and on another note - what would you use to make the TV light flicker?
I’m currently using noise modifiers for the lights, but someone (that uses vray) told me he would do it only in the comp.

Thanks in advance
Tal

Put objects on their own layer
Full scene AO pass and then use a mask to control where in the composition you want the AO to have any influence

I’m currently using noise modifiers for the lights, but someone (that uses vray) told me he would do it only in the comp.
You can keyframe parameters in nodes (mix factors etc) then you can use modifiers for those keyframes.

Thanks for the input Richard, good idea! I was putting the object’s ID mask with lots of blur on it as a mask for the AO , so the blur spreads around the object, and it works great.

regarding the flickering, I was wondering what would be better. doing it in compositing is good to have for better control, and maybe less noise,
but maybe doing the noise in the light itself is getting more realistic results? because it influences each object differently, especially if I’m going to use volumetrics