javascript-barcode-reader/src/utilities/adaptiveThreshold.ts

Simple & Fast Barcode decoder for Browser and Node.js

export function applyAdaptiveThreshold(
  data: Uint8ClampedArray,
  width: number,
  height: number
): Uint8ClampedArray {
  const integralImage = new Array(width * height).fill(0)
  const channels = data.length / (width * height)
  const t = 0.15 // threshold percentage
  const s = Math.floor(height) // bracket size
  const s2 = Math.floor(s / 2)

  for (let i = 0; i < width; i += 1) {
    let sum = 0
    for (let j = 0; j < height; j += 1) {
      const pureIndex = j * width + i
      const index = pureIndex * channels
      // greyscale
      const v = (data[index] + data[index + 1] + data[index + 2]) / 3

      data[index] = v
      data[index + 1] = v
      data[index + 2] = v
      sum += v

      if (i === 0) {
        integralImage[pureIndex] = sum
      } else {
        integralImage[pureIndex] = integralImage[pureIndex - 1] + sum
      }
    }
  }

  // skip edge rows
  for (let i = 0; i < width; i += 1) {
    for (let j = 0; j < height; j += 1) {
      const pureIndex = j * width + i
      const index = pureIndex * channels
      // no. of pixels per window
      let x1 = i - s2
      let x2 = i + s2
      let y1 = j - s2
      let y2 = j + s2

      if (x1 < 0) x1 = 0
      if (x2 >= width) x2 = width - 1
      if (y1 < 0) y1 = 0
      if (y2 >= height) y2 = height - 1

      const count = (x2 - x1) * (y2 - y1)
      const sum =
        integralImage[y2 * width + x2] -
        integralImage[y1 * width + x2] -
        integralImage[y2 * width + x1] +
        integralImage[y1 * width + x1]
      let v = 255

      if (data[index] * count < sum * (1 - t)) {
        v = 0
      }

      data[index] = v
      data[index + 1] = v
      data[index + 2] = v
    }
  }

  return data
}