Question

我在画布上放了一个图像，当用户将鼠标移到图像上时，我希望获得该图像像素的RGB值。这是我写的代码：

<canvas id="myCanvas" width="200" height="200" style="border: red;border-style: dotted">
Your browser does not support the canvas element.
</canvas>
<script>
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");

var destX = 0;
var destY = 0;

var imageObj = new Image();
imageObj.onload = function()
{
context.drawImage(imageObj, destX, destY);
};
imageObj.src = "zain.jpg";

canvas.onclick = function(e) {
    var x = e.pageX;
    var y = e.pageY;
    var canvasColor = context.getImageData(x, y, 1,1); // rgba e [0,255]
    var pixels = canvasColor.data;
    var r = pixels[0];
    var g = pixels[1];
    var b = pixels[2];
    document.body.style.backgroundColor = "rgb("+r+','+g+','+b+")";
}

Answer 1

尝试一下这个：

var color = document.getElementById("color");
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");

var imageObj = new Image();
imageObj.onload = function(){
    context.drawImage(imageObj, destX, destY);
};
imageObj.src = "zain.jpg";

canvas.onmousemove = function(e) {
    // not so sure about these... might need to offset them or so
    var x = e.x;
    var y = e.y;

    // set color now
    var canvasColor = context.getImageData(x, y, 1, 1).data; // rgba e [0,255]
    var r = canvasColor[0];
    var g = canvasColor[1];
    var b = canvasColor[2];

    color.style.backgroundColor = 'rgb(' + r + ',' + g + ',' + b + ')';
}

请注意，该代码段要求您在某处使用ID为“color”的div。它设置了那里的像素颜色。

Answer 2

您在这里寻找的是getImageData()电话。

所以，你的解决方案看起来像这样：

function getColor(canvas, x, y) {    
    var context = canvas.getContext("2d");
    var pixel = context.getImageData(x, y, 1, 1);

    // Red = rgb[0], green = rgb[1], blue = rgb[2]
    // All colors are within range [0, 255]
    var rgb = pixel.data;

    return rgb;
}

function canvasMouseMove(e) {
    var x = e.layerX, y = e.layerY;
    var rgb = getColor(canvas, x, y);
    var rgb_string = "rgb(" + rgb[0] + "," + rgb[1] + "," + rgb[2] + ")";

    document.body.style.backgroundColor = rgb_string;
}

canvas.onmousemove = canvasMouseMove;

正如@bebraw指出的那样，您可能需要根据所使用的浏览器不同地处理鼠标位置。为此，您可以考虑使用jQuery或其他JS库来简化。

读取画布像素的RGB值

2 个答案: