获取图片平均色

/**
 * 获取图片平均色
 */
export async function getImageAverageColor(
  image: HTMLImageElement,
): Promise<{
  r: number
  g: number
  b: number
}> {
  const canvas = document.createElement('canvas')
  const ctx = canvas.getContext('2d')
  if (!ctx) {
    throw new Error('CanvasRenderingContext2D is null')
  }
  canvas.width = image.width
  canvas.height = image.height
  ctx.drawImage(image, 0, 0)
  const colors = ctx.getImageData(0, 0, image.width, image.height).data

  let r = 0
  let g = 0
  let b = 0

  for (let i = 0; i < colors.length; i += 4) {
    r += colors[i]
    g += colors[i + 1]
    b += colors[i + 2]
  }

  r = Math.round(r / (image.width * image.height))
  g = Math.round(g / (image.width * image.height))
  b = Math.round(b / (image.width * image.height))

  return { r, g, b }
}