COLOR MATHS: POSTERIZE

Posterization is the process of reducing the number of different colours in a picture. Originally, it was done to reduced the cost of printing posters, as each individual colour in the picture would increase the cost of printing. In Poser we can produce this effect using three colour maths nodes.

To produce the posterise effect, we need to reduce the level of detail in the picture. Remember, Poser colour maths treats each colour channel as a number running from zero to one, with zero producing black and all ones produces white, so we can use simple maths on the channels.

We are going to use the round function to produce our bands. This would normally only produce two band for each colour channel - try pluging your picture directly into the Round node and see the result. We need a way to increase the number of bands produced. To do this, we are going to multiply our picture to produce a wider range of numbers, plug that into the round function, then divide the output by the same amount to bring our results back into the normal colour range.

Step one is to plug our picture into the Multiply colour maths node. We are going to create a User_Defined colour node to control our posterize. Here, we have set the red, green and blue values to three. This means that our colour channels now range from 0-3 instead of from 0-1.

Step two is to plug this output into our Round colour maths node. This rounds its input to the nearest whole numbers, so now instead of having a smooth spread of numbers between 0 and 3, we now only have 0, 1, 2 and 3.

Finally, we need to bring this back into the normal 0-1 range for colours. To do this, we create a Divide color maths node, plug the output from the round into Value 1, and the User_Defined colour into Value 2. Our colour channels now contain 0, 0.33, 0.66 and 1, giving four bands of colour. The three channels of colour are combined to produce the final result, giving us a total of sixty four different colours (4 times 4 times 4).

Fig 1: Posterize Node setup

Varients

If you want to alter the number of colours in the final result, then change the User_Defined values.

Lower values will reduce the number of colour bands, and thus the overall number of potential colours - a value of 2 will produce three colour values in each channel, for a total of twenty seven different colours. Increasing the values will produce more colour bands, although with much higher numbers the final result becomes quite hard to spot - even a value of 4 will produce 125 different colours.

You can pick out one or two colour channels by setting one or more of the User_Defined colours to zero. Try setting Green and Blue to zero and leaving Red as three - the final picture will have four shades of colour, ranging from black to bright red.