Filter Weighting Functions API

Weighting functions are responsive for pixel color weights, depending on how far pixels are from EWA ellipse center.

WeightingFunction interface

interface WeightingFunction {
  (x: number, support: number, windowSupport: number): number;
}

WeightingFunctionFactory interface

WeightingFunctionFactory interface creates weighting functions.

interface WeightingFunctionFactory<FactoryArgs extends number[] = number[]> {
  create(...args: FactoryArgs): WeightingFunction;
}

The create() method of weighting function factory may accept arguments which may be used to calculate weighting function arguments.

Example from lens source - CubicBC() function factory:

export class CubicBCFactory
  implements WeightingFunctionFactory<[number, number]>
{
  /**
   * Creates cubicBC() function.
   *
   * @param b B value.
   * @param c C value.
   */
  create(b: number, c: number): WeightingFunction {
    const p0 = (6 - 2 * b) / 6;
    // const p1 = 0;
    const p2 = (-18 + 12 * b + 6 * c) / 6;
    const p3 = (12 - 9 * b - 6 * c) / 6;
    const q0 = (8 * b + 24 * c) / 6;
    const q1 = (-12 * b - 48 * c) / 6;
    const q2 = (6 * b + 30 * c) / 6;
    const q3 = (-1 * b - 6 * c) / 6;

    return function cubicBC(x?: number): number {
      if (typeof x === "number") {
        if (x < 1) {
          return p0 + x * (x * (p2 + x * p3));
        } else if (x < 2) {
          return q0 + x * (q1 + x * (q2 + x * q3));
        }
      }
      return 0;
    };
  }
}

WeightingFunctionFactoryPool type

Pool of WeightingFunctionFactory implementations, which keys are WeightingFunctionName enum values.

interface WeightingFunctionFactoriesPoolKeyMap {
  [WeightingFunctionName.BOX]: BoxFactory;
  [WeightingFunctionName.CUBIC_BC]: CubicBCFactory;
  [key: string]: WeightingFunctionFactory;
}

type WeightingFunctionFactoriesPool = Pool<
  WeightingFunctionFactory,
  WeightingFunctionFactoriesPoolKeyMap
>;