Color Manipulation

<!--
  说明：像素级颜色运算的中文示例，数据在页面内生成，可独立运行。
  核心逻辑：getImageData 逐像素运算 + 颜色矩阵 + canvas 重绘
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>像素级颜色运算</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:10px;align-items:center;flex-wrap:wrap;font-size:12px;color:#58606e}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar button{font:inherit;padding:3px 9px;border:1px solid #c9ced6;background:#fff;
       border-radius:5px;cursor:pointer;color:#333}
  .bar button:hover{background:#eef2f8}
  .bar input[type=range]{width:110px;vertical-align:middle}
  .bar input[type=text]{font:inherit;padding:2px 6px;border:1px solid #c9ced6;border-radius:4px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3;position:relative}
  .panel{flex:0 0 auto;max-height:34%;overflow:auto;padding:8px 12px;font-size:12px;
       background:#fff;border-top:1px solid #e3e6ea;color:#3d4451}
  .panel pre{margin:0;font-family:Consolas,"Courier New",monospace;font-size:11px;
       white-space:pre-wrap;word-break:break-all;line-height:1.5}
  .ol-attribution{font-size:11px}

</style>
</head>
<body>
<div class="bar">
<label>亮度 <input type="range" id="br" min="-100" max="100" value="0"></label>
<label>对比度 <input type="range" id="ct" min="-100" max="100" value="0"></label>
<label>饱和度 <input type="range" id="st" min="-100" max="100" value="0"></label>
<span id="info">—</span>
</div>
<div id="map"></div>

<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    var errBox = document.getElementById('map');
    if (errBox) {
      errBox.innerHTML = '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    }
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;
  var W = 320;
  var canvas = document.createElement('canvas');
  canvas.width = canvas.height = W;
  var ctx = canvas.getContext('2d');

  var g = ctx.createLinearGradient(0, 0, W, W);
  g.addColorStop(0, '#1b4f9c');
  g.addColorStop(0.45, '#f0c34a');
  g.addColorStop(1, '#c0392b');
  ctx.fillStyle = g;
  ctx.fillRect(0, 0, W, W);
  ctx.fillStyle = 'rgba(255,255,255,0.75)';
  for (var i = 0; i < 7; i++) {
    ctx.beginPath();
    ctx.arc(40 + i * 40, 80 + (i % 3) * 70, 18 + (i % 4) * 6, 0, Math.PI * 2);
    ctx.fill();
  }
  ctx.fillStyle = 'rgba(20,30,45,0.65)';
  ctx.fillRect(0, W - 70, W, 70);

  var base = ctx.getImageData(0, 0, W, W);
  var raw = new Uint8ClampedArray(base.data);
  var image = ctx.createImageData(W, W);

  var extent = ol.proj.transformExtent([115.9, 39.5, 116.9, 40.4], 'EPSG:4326', 'EPSG:3857');
  var layer = new ol.layer.Image();

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'})}), layer],
    view: new ol.View({center: fromLonLat([116.4, 39.9]), zoom: 11}),
    controls: ol.control.defaults.defaults({attribution: false, zoom: true, rotate: false})
  });

  var br = document.getElementById('br');
  var ct = document.getElementById('ct');
  var st = document.getElementById('st');
  var info = document.getElementById('info');

  function apply() {
    var bright = +br.value;
    var contrast = 1 + (+ct.value) / 100;
    var sat = 1 + (+st.value) / 100;

    for (var i = 0; i < raw.length; i += 4) {
      var r = (raw[i] - 128) * contrast + 128 + bright;
      var g2 = (raw[i + 1] - 128) * contrast + 128 + bright;
      var b = (raw[i + 2] - 128) * contrast + 128 + bright;

      var gray = 0.299 * r + 0.587 * g2 + 0.114 * b;
      image.data[i] = gray + (r - gray) * sat;
      image.data[i + 1] = gray + (g2 - gray) * sat;
      image.data[i + 2] = gray + (b - gray) * sat;
      image.data[i + 3] = raw[i + 3];
    }

    ctx.putImageData(image, 0, 0);
    layer.setSource(new ol.source.ImageStatic({
      url: canvas.toDataURL('image/png'),
      imageExtent: extent,
      projection: 'EPSG:3857'
    }));
    info.textContent = '亮度 ' + bright + ' · 对比度 ×' + contrast.toFixed(2) +
      ' · 饱和度 ×' + sat.toFixed(2);
  }

  var timer = null;
  function schedule() {
    if (timer) { return; }
    timer = setTimeout(function () {
      timer = null;
      apply();
    }, 90);
  }

  br.addEventListener('input', schedule);
  ct.addEventListener('input', schedule);
  st.addEventListener('input', schedule);
  apply();
})();
</script>
</body>
</html>