Generation Process: Multiple Generation Population (MPG)

GenShade Process

Multiple Generation Population (MGP)

GenShade uses a multiple-generation population of shaders to maintain a large and diverse population, avoid stagnation, and give higher opportunity to strong genetic material. This architecture preserves a large set of the best scored shaders across a range of generations. In this way, artists experiment knowing that there is nothing to lose by producing a generation of "poor" shaders. In the worst case, the population will remain essentially the same. Usually, the maximum population size is set between two and three hundred. Shaders are inserted into the population in sorted order, if automatic scoring is on, with higher scored shaders replacing lower scored ones when the population maximum is exceeded. The multiple-generation population allows parents and children to coexist in the same population, which models an important feature of natural evolution. Initially, the system retrieves shaders from a predefined database of shaders and inserts the best scored shaders into these populations. Shaders are inserted into male and female populations based on their image scoring. Shaders that score high on illumination are called the "male" shaders and those that score high on chromaticity the "female" shaders. This organization is used in selection, which is described below.

The main pool contains the best shaders generated so far, sorted based on their overall score considering both illumination and chromaticity. In every generation, the pool is updated by new generated shaders. At the end, the user interactively selects desired shaders from the output pool. Since the output pool has no concept of aging, it contains the best shaders over all generations. An output pool of 200, the maximum size, has been used for experiments described in this study, with new higher scored shaders replacing lower scored shaders when this maximum is exceeded. The New Pool contains the best new shaders generated so far.

Aging is simulated in the multiple-generation population, to allow successful shaders several opportunities to produce direct offspring, while assuring that no single shader continues to dominate the population for-
ever. This provides a good balance between keeping strong genetic material in the pool and assuring diversity in the population.

If interactive scoring is on, the MGP pools would not be updated every generation simply because there is no score. Shaders would be selected then from the initial MGP pools based on their rank. For example, a shader ranked 1st would have much more chance of getting selected than one that is ranked 50.

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