imagedata-filters/src/filters/grayscale.js

some filters for imagedata of canvas context2d

export default grayscale

function grayscale (imagedata, opts) {
    var i = 0
    var data = imagedata.data
    var len = data.length
    var opts = opts || {amount: 0}
    var amount = +opts.amount || 0
    var compleAmount = 1 - amount
    var r,g,b
    for (; i < len; i += 4) {
        r = (0.2126 + 0.7874 * compleAmount) * data[i]
            + (0.7152 - 0.7152 * compleAmount) * data[i + 1]
            + (0.0722 - 0.0722 * compleAmount) * data[i + 2]
        g = (0.2126 - 0.2126 * compleAmount) * data[i]
            + (0.7152 + 0.2848 * compleAmount) * data[i + 1]
            + (0.0722 - 0.0722 * compleAmount) * data[i + 2]
        b = (0.2126 - 0.2126 * compleAmount) * data[i]
            + (0.7152 - 0.7152 * compleAmount) * data[i + 1]
            + (0.0722 + 0.9278 * compleAmount) * data[i + 2]
        data[i] = r
        data[i + 1] = g
        data[i + 2] = b
    }

    return imagedata
}