True Shadow Pass

Overview

Poser's shadow only pass may not give desirable results. Often, it's just wrong and difficult to composite. Using two lighting passes, you can get the true shadows of your scene.

Setting up the render job

Use whatever settings you like for your render job. You'll need at least these two passes to extract the shadows:

The lite Pass

This pass is GlowWorm's shading pass preset. It's a lighting pass with shadows selected.

The lt Pass

This is a lighting pass without shadows selected. Optionally, you can create this pass from a pass for each light.

Compositing the two passes

In Photoshop (or whatever image editor you prefer), paste the lt pass on top of the lite pass. Set the lt pass's layer mode to "Difference".

Merge the layers and invert them to get your true shadows.

Compositing the true shadow pass with your image

Paste the true shadow pass on top of your image and set its layer mode to "Linear Burn" (aka "Subtract"). You can now control the color and intensity of shadows as you please.