js小计谋：提取图像内小球数量，玩出小创意！

引言

图像是由连续的点信息组成的，每个点信息包含四个长度即rgba信息，通过遍历配合处理函数实现对点个数的判断。本例子采用png格式图片，只需要判该点透明度（opacity）是否为0即可确定是否为小球上一点，如果不为0，判断上下左右方向的点是否透明度为0，不为0递归该结果，并且将该点对应的rgba信息设置为(0,0,0,0)，即透明。判断完上下左右四个点，判断斜角四个方向的点。递归结束后，计数满足条件的点数量即可。

JavaScript算法

function countPoints(image) {
  // Get the image data from the canvas
  var canvas = document.createElement('canvas');
  canvas.width = image.width;
  canvas.height = image.height;
  var context = canvas.getContext('2d');
  context.drawImage(image, 0, 0);
  var imageData = context.getImageData(0, 0, image.width, image.height);

  // Create an array to store the visited pixels
  var visited = [];
  for (var i = 0; i < imageData.data.length; i += 4) {
    visited.push(false);
  }

  // Count the number of points
  var count = 0;
  for (var i = 0; i < imageData.data.length; i += 4) {
    if (visited[i] || imageData.data[i + 3] === 0) {
      continue;
    }

    // Mark the pixel as visited
    visited[i] = true;

    // Recursively count the number of points in the neighborhood
    count += countNeighbors(imageData, i, visited);
  }

  return count;
}

function countNeighbors(imageData, i, visited) {
  // Get the coordinates of the pixel
  var x = i % imageData.width;
  var y = Math.floor(i / imageData.width);

  // Check if the pixel is on the edge of the image
  if (x === 0 || x === imageData.width - 1 || y === 0 || y === imageData.height - 1) {
    return 1;
  }

  // Check if the pixel is surrounded by transparent pixels
  var count = 0;
  for (var j = -1; j <= 1; j++) {
    for (var k = -1; k <= 1; k++) {
      if (j === 0 && k === 0) {
        continue;
      }

      var index = (x + j) + (y + k) * imageData.width;
      if (visited[index] || imageData.data[index + 3] === 0) {
        count++;
      }
    }
  }

  return count;
}

使用示例

<img id="image" src="image.png" />

var image = document.getElementById('image');
var count = countPoints(image);
console.log('Number of points:', count);

结论

使用JavaScript可以轻松计算图像中的点的数量。该算法可以用于各种图像处理应用，如图像分割、目标检测和图像压缩。