RGBA format HEX into RGB format HEX? PHP

问题:

I want to convert back and forth between RGBA-formated HEX colors (like0xFF0000FF) and RGB-formated HEX colors (like 0xFF0000) in PHP.

How can I do this?

回答1:

How about these:

function rgbaToRgb ($rgba, $blend = 0xFFFFFF) {
    return (($rgba >> 8)*($rgba & 0xFF)/0xFF) * ($blend / 0xFFFFFF);
}

function rgbToRgba ($rgb) {
    return ($rgb << 8) | 0xFF;
}

$blend in the first is effectively a background color to blend with.

Edit: fix due to not enough space in ints ruining RGBA. RGBA is now handled as a four part array. RGB remains a number.:

function rgbaToRgb ($rgba, $blend = 0xFFFFFF) {
$rbg = array($rgba[0] * $rgba[3]/0xFF + ($blend>>16) * (0xFF-$rgba[3])/0xFF, $rgba[1] * $rgba[3]/0xFF + (($blend>>8)&0xFF)*(0xFF-$rgba[3])/0xFF, $rgba[2] * $rgba[3]/0xFF + ($blend&0xFF) * (0xFF-$rgba[3])/0xFF);
return ($rbg[0]<<16) + ($rbg[1]<<8) + $rbg[2];
}

function rgbToRgba ($rgb) {
    return array($rgb >> 16, ($rgb >> 8) & 0xFF, $rgb & 0xFF, 0xFF);
}

回答2:

These two functions will do what you need:

function rgbaToRgb ($rgba) {
    return substr($rgba, 0, -2);
}

function rgbToRgba ($rgb) {
    return $rgb . "FF";
}

The first one simply removes the last two characters, whilst the second one simply appends FF.

回答3:

RGBA -> RGB should be simple, as it's just cutting off the last two digits. The other direction is impossible, as alpha information isn't encoded in RGB.

回答4:

As Frank mentioned, you can simply strip the last 2 digits.

The hex format is 3 pairs of numbers, the first pair Red value, the next is Green, and the next is blue. If you add another pair, it's assumed to be the alpha value.