i founded this piece of code here on stack:

``function increase_brightness(hex, percent){var r = parseInt(hex.substr(1, 2), 16),g = parseInt(hex.substr(3, 2), 16),b = parseInt(hex.substr(5, 2), 16);return '#' +((0|(1<<8) + r + (256 - r) * percent / 100).toString(16)).substr(1) +((0|(1<<8) + g + (256 - g) * percent / 100).toString(16)).substr(1) +((0|(1<<8) + b + (256 - b) * percent / 100).toString(16)).substr(1);}``

does anyone knows how to make the exactly inverse?

function `decreas_brightness(){}` i mean

Your code is from Javascript Calculate brighter colour. According to the comments, the following change should make it decrease brightness:

``````function decrease_brightness(hex, percent){
var r = parseInt(hex.substr(1, 2), 16),
g = parseInt(hex.substr(3, 2), 16),
b = parseInt(hex.substr(5, 2), 16);

return '#' +
((0|(1<<8) + r * (100 - percent) / 100).toString(16)).substr(1) +
((0|(1<<8) + g * (100 - percent) / 100).toString(16)).substr(1) +
((0|(1<<8) + b * (100 - percent) / 100).toString(16)).substr(1);
}
``````

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