如何使用HSL到RGB转换功能 [英] How to Use HSL to RGB Conversion Function

问题描述

感觉我在这里缺少一些非常简单的东西，但是我不能得到从 HSL到RGB颜色转换工作。有问题的函数是：

Feel like I'm missing something really simple here, but I can't get the formula posted from an answer from HSL to RGB color conversion to work. The function in question is:

function hslToRgb(h, s, l){
    var r, g, b;

    if(s == 0){
        r = g = b = l; // achromatic
    }else{
        function hue2rgb(p, q, t){
            if(t < 0) t += 1;
            if(t > 1) t -= 1;
            if(t < 1/6) return p + (q - p) * 6 * t;
            if(t < 1/2) return q;
            if(t < 2/3) return p + (q - p) * (2/3 - t) * 6;
            return p;
        }

        var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
        var p = 2 * l - q;
        r = hue2rgb(p, q, h + 1/3);
        g = hue2rgb(p, q, h);
        b = hue2rgb(p, q, h - 1/3);
    }

    return [Math.round(r * 255), Math.round(g * 255), Math.round(b * 255)];
}

我想问的是， h'参数。通常，当在CSS或Photoshop中使用HSL时，色调值是介于0和360之间的数字，但此函数要求在0和1之间的值。有人可以向我解释我将如何转换色调值的240到0和1之间的等价值，所以我可以把它插入这个公式？我尝试将240除以360，但这不起作用。

My issue, I believe, is in regard to what to enter as my 'h' parameter. Typically, when using HSL in CSS or Photoshop, the hue value is a number between 0 and 360, but this function calls for a value in between 0 and 1. Can someone explain to me how I would, for example, convert a hue value of 240 to the equivalent value between 0 and 1, so I can plug it into this formula? I tried dividing 240 by 360, but this did not work.

推荐答案

看起来原始算法是错误的。根据维基百科，您可以获得色度&亮度调整独立于色调（因此类似的b值），但任何事情需要更多的数学特定模。它看起来不像那个算法处理那个特定的转换很好，特别是考虑到它期望色调在范围[0，1]。尝试此算法：

Looks like the original algorithm is wrong. According to wikipedia, you can get the chroma & lightness adjustments independent of hue (hence the similar b value), but anything else requires a little more math—specifically modulo. It doesn't look like that algorithm handles that particular conversion well, especially considering it expects hue to be in the range [0, 1]. Try this algorithm instead:

// expected hue range: [0, 360)
// expected saturation range: [0, 1]
// expected lightness range: [0, 1]
var hslToRgb = function(hue, saturation, lightness){
  // based on algorithm from http://en.wikipedia.org/wiki/HSL_and_HSV#Converting_to_RGB
  if( hue == undefined ){
    return [0, 0, 0];
  }

  var chroma = (1 - Math.abs((2 * lightness) - 1)) * saturation;
  var huePrime = hue / 60;
  var secondComponent = chroma * (1 - Math.abs((huePrime % 2) - 1));

  huePrime = Math.floor(huePrime);
  var red;
  var green;
  var blue;

  if( huePrime === 0 ){
    red = chroma;
    green = secondComponent;
    blue = 0;
  }else if( huePrime === 1 ){
    red = secondComponent;
    green = chroma;
    blue = 0;
  }else if( huePrime === 2 ){
    red = 0;
    green = chroma;
    blue = secondComponent;
  }else if( huePrime === 3 ){
    red = 0;
    green = secondComponent;
    blue = chroma;
  }else if( huePrime === 4 ){
    red = secondComponent;
    green = 0;
    blue = chroma;    
  }else if( huePrime === 5 ){
    red = chroma;
    green = 0;
    blue = secondComponent;
  }

  var lightnessAdjustment = lightness - (chroma / 2);
  red += lightnessAdjustment;
  green += lightnessAdjustment;
  blue += lightnessAdjustment;

  return [Math.round(red * 255), Math.round(green * 255), Math.round(blue * 255)];

};

它可能会在几个边缘情况下失败，但这些应该很容易修复

It may fail on a few edge cases, but those should be easy fixes

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