image-js/src/operations/extract.ts

Image processing and manipulation in JavaScript

import { Image } from '../Image.js';
import type { Mask } from '../Mask.js';
import type { Point } from '../utils/geometry/points.js';
import { assert } from '../utils/validators/assert.js';
import { checkPointIsInteger } from '../utils/validators/checkPointIsInteger.js';

export interface ExtractOptions {
  /**
   * Origin of the ROI relative to a parent image (top-left corner).
   * @default `{row: 0, column: 0}`
   */
  origin?: Point;
}

/**
 * Extract the pixels of an image, as specified in a mask.
 * @param image - The image to process.
 * @param mask - The mask defining which pixels to keep.
 * @param options - Extract options.
 * @returns The extracted image.
 */
export function extract(
  image: Image,
  mask: Mask,
  options: ExtractOptions = {},
): Image {
  const { origin = { row: 0, column: 0 } } = options;
  const { row, column } = origin;

  assert(
    row < image.height &&
      column < image.width &&
      row + mask.width > 0 &&
      column + mask.height > 0,
    'extract: image and mask have no overlap',
  );

  checkPointIsInteger(origin, 'Origin');

  const resultWidth =
    Math.min(image.width, mask.width + column) - Math.max(0, column);
  const resultHeight =
    Math.min(image.height, mask.height + row) - Math.max(0, row);

  let newImage = new Image(resultWidth, resultHeight, {
    colorModel: image.colorModel,
    origin,
  });

  if (newImage.alpha) {
    newImage = newImage.fillAlpha(0);
  }

  const imageStartRow = Math.max(0, row);
  const imageStartColumn = Math.max(0, column);
  const maskStartRow = row < 0 ? -row : 0;
  const maskStartColumn = column < 0 ? -column : 0;

  for (let resultRow = 0; resultRow < resultHeight; resultRow++) {
    for (let resultColumn = 0; resultColumn < resultWidth; resultColumn++) {
      if (
        mask.getBit(maskStartColumn + resultColumn, maskStartRow + resultRow)
      ) {
        newImage.setPixel(
          resultColumn,
          resultRow,
          image.getPixel(
            imageStartColumn + resultColumn,
            imageStartRow + resultRow,
          ),
        );
      }
    }
  }
  return newImage;
}