octreequantisatie

Octree quantization is a color quantization algorithm used in computer graphics to reduce the number of colors in an image while trying to preserve the visual appearance. It is particularly useful for reducing the bit depth of an image, for example, when converting a 24-bit true-color image to an 8-bit indexed color image. The core idea is to represent the image's color space with a tree-like data structure called an octree.

The octree is built by recursively subdividing the color space. Initially, the entire RGB color cube is considered the root node. As pixels from the image are processed, they are placed into the appropriate node in the octree. If a node contains too many pixels or exceeds a predefined depth, it is subdivided into eight smaller child nodes, representing a further division of the color space along each of the R, G, and B axes. This process continues until a stopping condition is met, such as reaching a maximum depth or a minimum number of pixels per leaf node.

Once the octree is constructed, it is pruned to create a limited number of representative colors. Leaf nodes that contain pixels are aggregated to determine their average color. The octree is then collapsed by merging nodes until the desired number of colors is reached. Typically, nodes with fewer pixels are merged into their parent nodes. The representative colors are then chosen from the remaining leaf nodes.

When an image with reduced colors is generated, each original pixel's color is mapped to the closest representative color found in the octree. This approach tends to group similar colors together effectively, minimizing visual artifacts compared to simpler quantization methods. The octree structure allows for efficient storage and retrieval of color information during the quantization process.