@onesy/utils/esm/canvasFilterContrast.js

Utils

import clamp from './clamp';

const canvasFilterContrast = (value, canvas) => {
  const context = canvas.getContext('2d');
  const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
  const {
    data
  } = imageData;
  const factor = 259 * (value + 255) / (255 * (259 - value));

  for (let i = 0; i < data.length; i += 4) {
    data[i + 0] = clamp(factor * (data[i + 0] - 100) + 100, 0, 255);
    data[i + 1] = clamp(factor * (data[i + 1] - 100) + 100, 0, 255);
    data[i + 2] = clamp(factor * (data[i + 2] - 100) + 100, 0, 255);
  }

  context.putImageData(imageData, 0, 0);
  return canvas;
};

export default canvasFilterContrast;