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Add Adaptive color background

This code sample will allow you to add a smooth background gradient that takes into account the image itself when it does not fill the entire element.

function addAdaptiveBgColor(el) {
    var imgs = el.querySelectorAll('li');
    for (var i = 0; i < imgs.length; i++) {
        getImgColors(imgs[i]);
    }
}

function getImgColors(imgEl1) {
    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,
        rgbTop = {
            r: 0,
            g: 0,
            b: 0
        },
        rgbBottom = {
            r: 0,
            g: 0,
            b: 0
        },
        count = 0;
    if (!context) {
        return;
    }
    var imgEl = new Image();
    var theSrc = imgEl1.style.backgroundImage.replace('url(', '').replace(')', '');
    imgEl.src = theSrc;
    imgEl.onload = function () {
        height = canvas.height = imgEl.naturalHeight || imgEl.offsetHeight || imgEl.height;
        width = canvas.width = imgEl.naturalWidth || imgEl.offsetWidth || imgEl.width;
        context.drawImage(imgEl, 0, 0);
        topPixels = context.getImageData(0, 0, width, 3);
        bottomPixels = context.getImageData(0, height - 3, width, 3);
        length = 3 * width;
        while ((i += blockSize * 4) < length) {
            ++count;
            rgbTop.r += topPixels.data[i];
            rgbTop.g += topPixels.data[i + 1];
            rgbTop.b += topPixels.data[i + 2];
            rgbBottom.r += bottomPixels.data[i];
            rgbBottom.g += bottomPixels.data[i + 1];
            rgbBottom.b += bottomPixels.data[i + 2];
        }

        // ~~ used to floor values
        rgbTop.r = ~~(rgbTop.r / count);
        rgbTop.g = ~~(rgbTop.g / count);
        rgbTop.b = ~~(rgbTop.b / count);
        rgbBottom.r = ~~(rgbBottom.r / count);
        rgbBottom.g = ~~(rgbBottom.g / count);
        rgbBottom.b = ~~(rgbBottom.b / count);
        imgEl1.style.webkitTransition = 'all 1s';
        imgEl1.style.backgroundSize = 'contain';
        imgEl1.style.backgroundPosition = '50% 50%';
        imgEl1.style.backgroundImage += ', linear-gradient(rgb(' + rgbTop.r + ',' + rgbTop.g + ',' + rgbTop.b + '),rgb(' + rgbBottom.r + ',' + rgbBottom.g + ',' + rgbBottom.b + '))';
    };
}

Directions:
- create your HTML with image as background then call addAdaptiveBgColor(el)

Note:
This snippet is based on a slider that uses the ul li technique.
This snippet focuses on iOS development. Make sure to verify/adapt any vendor prefixes.

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