从javascript中的<div> CSS样式获取图像数据

Question

我有一个CSS样式,在它的背景中它有一个图像,例如它就像这个代码

.test {
    background-image: url("paper.gif");
    background-color: #cccccc;
}

我也有一个javascript代码,用于获取图像的平均颜色,

function getAverageRGB(imgEl) {

    var blockSize = 5, // only visit every 5 pixels
        defaultRGB = {r:0,g:0,b:0}, // for non-supporting envs
        canvas = document.createElement('canvas'),
        context = canvas.getContext && canvas.getContext('2d'),
        data, width, height,
        i = -4,
        length,
        rgb = {r:0,g:0,b:0},
        count = 0;

    if (!context) {
        return defaultRGB;
    }

    height = canvas.height = imgEl.naturalHeight || imgEl.offsetHeight || imgEl.height;
    width = canvas.width = imgEl.naturalWidth || imgEl.offsetWidth || imgEl.width;

    context.drawImage(imgEl, 0, 0);

    try {
        data = context.getImageData(0, 0, width, height);
    } catch(e) {
        /* security error, img on diff domain */alert('x');
        return defaultRGB;
    }

    length = data.data.length;

    while ( (i += blockSize * 4) < length ) {
        ++count;
        rgb.r += data.data[i];
        rgb.g += data.data[i+1];
        rgb.b += data.data[i+2];
    }

    // ~~ used to floor values
    rgb.r = ~~(rgb.r/count);
    rgb.g = ~~(rgb.g/count);
    rgb.b = ~~(rgb.b/count);

    return rgb;
    }

由于上面的代码显示我必须将一个图像元素传递给函数,但实际上我没有任何标记,我只有一个div,其css有一个背景图像,我怎样才能读取图像数据？thansk

Answer 1

您可以使用您的div background-img作为源创建一个Image元素.

img = new Image();
img.src = divTest.style.backgroundImage;