(Cycles, Beginner) - How you make a 3D object show Shadows on Background Photo

[mediumaevum]

This is my very first tutorial.
Easy on me, thanks

Let’s say you want a 3D object (in this tutorial, just a Cube) casting shadows on the ground in your background photo.

Like this:

• In Cycles, where there is no Shadow Only option, like in Internal.

First of all, load in your background photo and set it to be shown in your viewport.

Secondly, make sure that in Film-section in your Render Tab, the render is set to Transparent. This will make your background of your render an alpha image, so you can insert your background image.

Third, go into Camera Viewmode, and set Camera Lock To Viewport. Position the camera so that the Grid lines up with the floor/ground in your background image.

Next, insert a Plane, scale it up so it fits the ground.
Extrude the Edge in the horizon up the Z-axis so it covers the entire background image.

Place this plane on another layer (press M and choose a layer). In Layers Tab, rename your RenderLayer to “CubeLayerWithLights” (this makes it easier to see where we have our Cube and Lights) and uncheck the layer you placed your plane on! and create a second layer, rename it “Plane”. Set it to the layer where you have your plane covering your background image.

Then you go to the Node Editor and insert this Node Setup (always remember to set Use Nodes, I often forget this myself, giving me no results at all… ).

Image in the post below (my upload has reached a limit, sorry).

[mediumaevum]

Here is the node setup:

[Sakrecoer]

Thank you very much! I just had a AHA

Sorry for my n00bieness.

@reSet

How to you get rid of the all the other shadows, except the ones made by the cube (in other words, not the gradient of the plane)?

put that ground all over the place!

I have tried to knock the other shadows out with subtraction nodes, and by inverting another render layer that only shows the plane. But without success…

Tried to create a new project?

How to you get rid of the all the other shadows, except the ones made by the cube (in other words, not the gradient of the plane)?

there is only one way; noodle-fu.

@reSet Sakrecoer

1st of all: Thank you very much for this simple and clear tutorial!
But i get stuck on an ealry stage (/me waves n00b flag) as seen in the screen shot of the nodes, the render layer called “plane” is not only displaying shadow, when i use overlay, i get all the other shadows (plane gradient etc) mixed with my image. I have tried to knock the other shadows out with subtraction nodes, and by inverting another render layer that only shows the plane. But without success…

How to you get rid of the all the other shadows, except the ones made by the cube (in other words, not the gradient of the plane)?

edit—
this is driving me nuts hehe… been trying for weeks now

Now the shadow is there, but the plane is there too and putting up huge mark in the picture. The only workarround i could figure is to sort of draw a fake contour with the ground plane, but this makes it impossible to use if it’s animated… Or i would have to redraw the hole photo in 3d…?

I know there is no use for shadow path in your example, but the werid thing is that i cannot manage to get anything in the shadow path what so ever. with or without the shadows ticked in “light path”. Every render layer shadow path output in the compositor is giving me 100% black when plugged in the viewer… Is there anything i need to look for with the shadow path?