Shadow Pass Recipe

Intro to Layers

Ever notice that CG images tend to have really black shadows? The truth is, %100 black almost never occurs in real life.

The "Shadow Pass" recipe, mentioned here is good for all compositors. Give it a try next time you're comping a shadow pass.

Shadow Recipe

If you were planning on multiplying the shadows at 20% opacity, try 10% instead. Then duplicate the shadow layer and change the apply mode to overlay. On this second shadow pass, apply a levels operation and clip (reduce) the whites by %50. In other words, this overlay layer will have only %50 grey or darker in it.

That's it! Your shadows will be a rich dark color, but not overly black or muddy.

Basic composite example

The following example illustrates how a single CG element was hastily composited onto a photograph. This particular example was done in Photoshop, but the workflow is pretty much the same in Nuke, After Effects or any other package.

Step 1: Clean-up the image

The backplate (photo) was taken with an iPhone as the owner went to work. There were some obvious problems with it; Utility lines and hazard pylons just to name a few. These were edited out just to reduce the clutter of the image. Then the levels were adjusted to lighten the forground shadows a little.

Step 2: Import CG elements

The goal for this shot was to simply add a big bow to the building. The Giftbox Asset was used to creat a big ribbon around a box shape. A beauty pass and cast shadow pass were rendered.

Bear in mind, that in a production setting, this "beauty pass" would itself have been a composite of about 10 layers! e.g. Diffuse Color, Specular, Ambient Occlusion, Subsurface, Reflection etc..

Step 3: Shadows on the building

This is just a quick exercise, so only one beauty pass, and one cast shadow pass were created. This means that the shadows inside the bow itself will not benefit from the shadow pass recipe. It will only affect the shadows cast upon the building.

This shadow pass was rendered using a box as a stand-in for the building. This box had a shadowmatte material applied to it.

Some shadows had to be faked. In this case the shadow of the tree branches had to be added to the bow in order to match the building.

Step 4: Re-Apply Foreground

The foreground fence, tree branches and utility pole, needed to be duplicated from the background, and then re-applied over the bow. This was a manual masking or roto task. The edges of this foreground layer needed to be blurred so as to not appear overly sharp and artificial.

Step 5: Final Composite

Here is the composited image: A gift wrapped building. Some nice touches would be to adjust the bows color levels a bit, to add a specular pass, and maybe some noise to further sell it's integration with the photograph.
Happy Holidays!

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