Rendering additional passes is common when we want to improve/modify our images in post-production.
One of the passes which are un-common to use is the VRayNormal (or the CGeometry_NormalShading for CoronaRenderer).
As you can see from the image, in the Normal pass, we can see a different color for every polygon direction. In this way, if we select one color, we’ll select all the polygons looking in the same direction: this is the usual way to work with the Normal pass.
What we’re going to learn it’s a different way to use the Normal pass: we can add lights, shadows, specular reflections without painting any masks.
1. Put a copy of the Normal pass on top of the original render.
2. Add a Hue/Saturation adjustment on top of the Normal Pass. Link them together by clicking ALT+LeftClick between them. We’re not going to use this for the moment.
3. Add a Channel Mixer adjustment on top of the Hue/Saturation, and link it to it. Turn on the “Monochrome” option.
4. There’re no magic values for the three sliders, so I cannot tell you how to set them, but it could be a good starting point to move the red on the left, the green, and the blue on the right. As you can see, the Normal pass turned into a very contrasted light/shadow image. But can we move the light? Yes, we can, and it’s pretty easy, shifting the Normal pass colors.
5. Go back in the Hue/Saturation adjustment and move the Hue slider.
TA-DA! Now you’re able to get the effect/mask you need. You can create a mask and use it for some Curve adjustment or change the blending mode of the normal map (multiply for shadows, screen/lighten/color dodge for lights).
In this example, we added a realistic light on the armchair, using the result as a mask for a curve. Working on the red and blue channels, we also added a subtle yellow color. Remember, to get a mask of the visible layers, go into Channels and CTRL-LeftClick on a single channel thumbnail, then go back into layers and pick an adjustment while the selection is still active.
See ya next time!