MATHS: BIAS

This function is effectively the brightness node. The 'bias' it refers to is the balance between light and dark, or how 'biased' towards black or white your picture is.

To use the bias function, we plug our input node into value_1, normally with the actual value set to 1, then set value_2 to our required bias setting (although another node can be plugged in here to control the result).

To demonstrate the results of various bias settings, we have used the displacement channel. To get our control image (in red), we have plugged a U node straight into the displacement channel of a flat plane. This shows us the U node growing smoothly from zero (on the left) to one (on the right). To get the green image, we have plugged the output of the U node into a bias node, and the output of the bias node into the displacement (see figure 3).

Figure 1 shows the result of setting value_2 to 0.2. This 'biases' our output towards black. The modified output will be darker than the original pictures. Black and white are unchanged, while the middle shades are most altered.

Fig 1: Bias at 0.2

Figure 2 shows the same thing with a bias setting of 0.8. This time the output is raised, producing a 'bias' towards 1 (white). Any input node modified in this way will be brightened. Here, the darker areas are most the most altered.

Fig 2: Bias at 0.8

Figure 3 shows the node setup used to create these effects. The Displacement figure is set very high to produce the exaggerated visuals we need to see what is happening. The effect of the bias setting can be seen on the Bias node preview, where the output is much darker than the original U node that is being plugged into it.

Fig 3: The test nodes

Figure 4 shows the results of a bias node set to 0.8 acting on a greyscale photo. Most of the picture has got much brighter, although the darkest area (the bush to the centre left) is still dark, showing that the darker areas still stay dark even with quite a high bias setting.

Fig 4: Example Brightness

Suggested Uses

Try setting value_2 to 1, and then plugging a V node into it. This will brighten the top of the picture and darken the bottom.