AE question of the day: Cloud Shadows

Ok... I'll be as brief as possible.

Been working on a shot for a couple of days now. Sith Warriors marching below a castle cliff (from center of shot coming towards exit left.) with a flowing figure in the distance - large building in the background.

Here is what I did:
Recomposited the sky - did some minor tweaking, added an overlay layer with a gauss blur of about 3 - 5, set rgb values accordingly to match the sky as well as some bright/contrast sets. I then realized that the sky should be creating a HUGE shadow effect over everything considering its contrast to the scene.

Here is what I tried:
turning the clouds layer into a 3d layer copy and pasting it over the foreground - creating a mask over the top of the foreground figures (so it doesnt show over the clouds) and attempting to animate it after setting it to overlay (without a layer beneath so it is mostly opaque), dropping the opacity and raising the contrast for a more shadowy effect. The color in that layer offsets any rgb tweaks I've made, and desaturating it definately does not help. Aside from that the motion is very flat, hard to track with the sky layer and doesnt seem to travel like a shadow would across the ground - seems more like a fog effect. I thought about making several masks around the foreground and distorting them, but it seems like a very hard way to a common sense issue. The shadows should be smaller in the distance as they travel down the face of the castle wall which is about fifty to sixty yards away, as well as the building which 5 - 600 yards away, and then change angle when it hits the ground and foreground figures. I also tried using a displacement map assigning the forground to it but no difference. Haven't tried mesh warp yet but I'm a bit skeptical. any ideas would be GREATLY appreciated.

 

I can't help you with the technical part...

But...Because clouds are closer to their light source, the shadow would move very slowly, if at all, during your scene. Your shadow most likely won't be moving at all (unless it was a long scene).

 

Actually, the opposite would be true.. any object closer to the light source casts larger, faster shadows than one far away. Hold your hand in front of a light bulb and wiggle a finger to see what I mean on it's shadows.

As for the problems with the shadows, Scud, I'd probably suggest (as usual) a 3D resolution to the problem. The sky itself can be put through a "quick and dirty" distortion to allow it to be used as a texture in 3D.. specifically, a cookie for a spotlight. Then you build up a very basic version of your landscape (very basic, I'm talking a bumpy plane for the ground and another flat plane for your castle, basic shapes only). Render out a shadow pass of the shadows playing along these rough shapes, then apply it via Multiply to your original footage. The motion won't be perfect as far as the shadows moving along the ground and castle, but it'll be close enough that the audience won't notice.

 

ACTUALLY...

The closer to the source the larger the shadow. Thus if I held my hand 5 ft. from a lamp (so that it casts a shadow on the wall) and move it slowly. Then moved my hand closer and moved it at the same speed the shadow will cover more surface area, and thus take longer to pass. Of course the more direct the light source is the less difference it makes. But the sun is a pretty broad source.

 

However, the shadow will be traveling faster -- in essence, it is succumbing to something called the distal velocity factor... Regardless, the clouds may be closer to their light source (the sun) but the distance is so negligible that it makes pretty much no difference at all. If the sun were where the moon is, maybe... but then we'd have bigger problems.

Anyway, Scud -- I agree. A 3D approach is probably your best bet.

 

Thanks guys - after messing with it for long enough and ending up with completely different results each time - I realized that in actuality, the shadows I want seem a bit unrealistic. The foreground figure shadows are too harsh and the sun is actually out of frame. I dont think the clouds would create such a dramatic effect in real life, so I think I'll go sans shadows for now.

I do believe that a more proficient AE user could have pulled it off, but for me it would have been too much effort for something that isnt totally necessary.

Now if I could only perfect the colored look of the new LOTR trailer...