konva/src/filters/Contrast.ts

import { Factory } from '../Factory';
import { Node } from '../Node';
import { getNumberValidator } from '../Validators';
/**
 * Contrast Filter.
 * @function
 * @memberof Konva.Filters
 * @param {Object} imageData
 * @example
 * node.cache();
 * node.filters([Konva.Filters.Contrast]);
 * node.contrast(10);
 */

export const Contrast = function(imageData) {
  var adjust = Math.pow((parseInt(this.contrast()) + 100) / 100, 2);

  var data = imageData.data,
    nPixels = data.length,
    red = 150,
    green = 150,
    blue = 150,
    i;

  for (i = 0; i < nPixels; i += 4) {
    red = data[i];
    green = data[i + 1];
    blue = data[i + 2];

    //Red channel
    red /= 255;
    red -= 0.5;
    red *= adjust;
    red += 0.5;
    red *= 255;

    //Green channel
    green /= 255;
    green -= 0.5;
    green *= adjust;
    green += 0.5;
    green *= 255;

    //Blue channel
    blue /= 255;
    blue -= 0.5;
    blue *= adjust;
    blue += 0.5;
    blue *= 255;

    red = red < 0 ? 0 : red > 255 ? 255 : red;
    green = green < 0 ? 0 : green > 255 ? 255 : green;
    blue = blue < 0 ? 0 : blue > 255 ? 255 : blue;

    data[i] = red;
    data[i + 1] = green;
    data[i + 2] = blue;
  }
};

/**
 * get/set filter contrast.  The contrast is a number between -100 and 100.
 * Use with {@link Konva.Filters.Contrast} filter.
 * @name Konva.Node#contrast
 * @method
 * @param {Number} contrast value between -100 and 100
 * @returns {Number}
 */
Factory.addGetterSetter(
  Node,
  'contrast',
  0,
  getNumberValidator(),
  Factory.afterSetFilter
);