Material Channels

[Albert D Hart]

I had a case come up in the SketchUp forum which was a good example of a place to use Material Channels (A feature of nXtRender Batch). The user was trying to render a theater with a black carpet, and the carpet kept rendering as a light color.

I created a similar scene with black walls, and a very dark carpet and got a rendering like this:

I explained how I could lower the brightness from 50 to 40 to make the entire scene darker.  But, or course, this make the whole scene darker.

And then I explained how I could user Material channels instead to darken just the carpet.

Material Channels can be used to make small color and brightness changes after rendering. It is often used to bright something - like to make the ceiling in this image whiter - but it can also be used to darken the carpet.

1. After rendering, left click on a pixel in the carpet and select "Change Color":

The dialog box shows the current average color of the pixels in the carpet RGB(70,70,70)

Use the sliders to adjust the color of the carpet. In this case, I dropped it to 30,30,30 to make it darker, without making the rest of the scene darker.

This works by adjusting the color of every pixel rendered in that color, to match the new average color.

Because of anit-aliasing, reflections, and reflected light considerations, Material Channels does not work for making major changes - such as making the carpet bright yellow - but it can be used to make smaller, especially intensity, changes to a material.