View Full Version : composition - how its done ?

03 March 2006, 02:40 PM
hey all

lately I have done a skyline model, finish car.
I want insert the car into a real photo.

(i have good anderstanding with lighting)

the real photo has found, and my praimery problam is with the shadow. I put a box under the car for the shadow, but - how do I make the box go away without the shadow?

thanks, amit

no fate
03 March 2006, 04:34 PM
Go to the object properties of the box and on the render tab check the box that says "unseen by camera".

03 March 2006, 06:26 PM
it make the shadow go aay with the object

03 March 2006, 07:43 PM
1) use a box under car, setup in the box surface, under the advanced options, alpha -> shadow density.
that mean in the alpha you can see obj and plane only where there is the shadow. after that you an compose and manage in photoshop.

2) render out different pass, with render export, and after that compose shadow with photoshop that allow you to control the correct blending.

03 March 2006, 07:46 PM
agreed with above.

this is something best solved in compositing. you can do it in the render, but the more advanced your renders and images get, the more you will probably realize that seperate passed for different elements is often the best way to go. Compositing shadows is a perfect example of that.

03 March 2006, 11:58 AM
I Did As you say but the shadow still fade out

maybe something on the metirial?

03 March 2006, 12:26 PM
Set your groundplane to use Front Projection and use the same image as in the background, and make sure your object is seen by camera.


This let you see the effect directly in the renderview, but as PixelInfected and Monovich described, it won't look as great as if you do it in PS or a compositing app (not to mention the level of control you get doing it in comp).

03 March 2006, 12:37 PM
Have you tried Front Projection Mapping?

Just map your photo to your box object using 'Front' under the projection type and also use it as your background image in the 'Compositing' tab. Experiment with the luminosity/diffuse relationship of the box's surface for a best match with the background.
Using this method, you can crudely match the shape of the road with your box object and the shadows will follow the contours.

It works really well and I'd say it's less advanced than rendering out passes.

Ah-my typing is very slow!

03 March 2006, 01:27 PM
Indeed. The Unseen by camera hint is plainly wrong (Unless what you´re after is a render of just the shadow. In that case you would make the CAR unseen by camera). You want to use Front Projection for the ground. The explanation that some people was giving above about shadow density isn´t for want you want to do. It´s used to get the alpha of the shadow so that you can render and treat it separately in compositing.

Once you add Front Projection to the ground you´ll see it nicely blending with the background, but either too dark or too light (usually too dark). Now you gotta play with the diffuse and/or luminosity of the ground plane, taking into account two factors:

- cranking up either of them for the plane (diff. or lum.) will make it brighter.
- the higher the luminosity, the less opacity for the shadow
- the higher the diffuse, the darker the shadow.

So you goal is to give values to the plane so that it dissapears with the background BUT playing wit those two values you can at the same time decide how much opacity the shadow will have. With Fprime this is pretty easy to get right.

The only problem that appears with this kind of scenes is that if you use anything that is NOT a distant light you gotta be sure the whole plane is evenly lit. Otherwise when you get it to disappear on one side, it shows on the other, and viceversa. This can go from moderately easy to fix, to really tough if your ground plane is very it can get tough, unless...

...unless you own Worley´s G2! :deal: In that case you forget about Diffuse or luminosity issues. You just give Front Projection to the plane, activate LSD at G2´s "lighting" tab from its surface panel and bang! Done. Just decide the color of the shadow, and/or its opacity from the "boosts" tab. Not to mention G2 preview will allow, not just to sample pixels, but also to compare them with others from the original pic and will show you the error amount! How cool is that!
G2 is definitily a huge addition to your weaponry if you´re into compositing.

03 March 2006, 01:39 PM
cool its working :D ! thanks guys

I will complete the rest of the aspects and upload a finish still

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03 March 2006, 01:39 PM
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