PHP 函数需要帮助：brightness();使 RGB 颜色更暗/更亮

Question

想象一个十六进制的有效 #RGB 颜色，定义为 $color = "#f7b9a0";

现在我想让 php 从这个 $color 派生出另外两种稍浅/稍深的颜色（相同的色调/颜色但只是改变了亮度）。我可以通过哪些方式实现这一目标？什么代码会生成这个？我感觉我需要一些简单的东西，比如：

brightness(input rgb color, ± number of steps); // function outputs the new RGB
 // ?? What php code should go here??

理想情况下，我希望在我的 html 中有这样的东西：

.classDefault {color:<?=$color?> }
.classLighter {color:<?=brightness($color,+10)?> } /* 10 steps brighter */
.classDarker  {color:<?=brightness($color,-25)?> } /* 25 steps darker   */

brightness(); 函数中应该包含什么 PHP 代码？为了我的梦想成真？
任何建议和/或代码都非常感谢！

---

从以下答案更新：

function alter_brightness($colourstr, $steps) {
  $colourstr = str_replace('#','',$colourstr);
  $rhex = substr($colourstr,0,2);
  $ghex = substr($colourstr,2,2);
  $bhex = substr($colourstr,4,2);

  $r = hexdec($rhex);
  $g = hexdec($ghex);
  $b = hexdec($bhex);

  $r = max(0,min(255,$r + $steps));
  $g = max(0,min(255,$g + $steps));  
  $b = max(0,min(255,$b + $steps));

  return '#'.dechex($r).dechex($g).dechex($b);
}

### NOW LETS DEFINE MY COLOR
$color = "#2233FF";

### DERIVED BRIGHTER COLORS
$color1 = brightness($color,25);
$color2 = brightness($color,50);
$color3 = brightness($color,75);

### DERIVED DARKER COLORS
$color4 = brightness($color,-25);
$color5 = brightness($color,-50);
$color6 = brightness($color,-75);


<!-- BRIGHTER -->
<div style=" background-color:<?=$color3?>"><?=$color3?></div>
<div style=" background-color:<?=$color2?>"><?=$color2?></div>
<div style=" background-color:<?=$color1?>"><?=$color1?></div>

<!-- DEFINED CONSTANT -->
<div style=" background-color:<?=$color?>"><?=$color?></div>

<!-- DARKER -->
<div style=" background-color:<?=$color4?>"><?=$color4?></div>
<div style=" background-color:<?=$color5?>"><?=$color5?></div>
<div style=" background-color:<?=$color6?>"><?=$color6?></div>

较亮的颜色有效，但较暗的颜色无效。哦，好吧，一半解决方案至少是解决方案的很大一部分，所以非常感谢！

Answer 1

沿着这些思路...

function alter_brightness($colourstr, $steps) {
  $colourstr = str_replace('#','',$colourstr);
  $rhex = substr($colourstr,0,2);
  $ghex = substr($colourstr,2,2);
  $bhex = substr($colourstr,4,2);

  $r = hexdec($rhex);
  $g = hexdec($ghex);
  $b = hexdec($bhex);

  $r = max(0,min(255,$r + $steps));
  $g = max(0,min(255,$g + $steps));  
  $b = max(0,min(255,$b + $steps));

  return '#'.dechex($r).dechex($g).dechex($b);
}

调用 $colour = alter_brightness('#2233FF',5);

Answer 2

Cintia 几乎是正确的，但是 str_pad 应该在之前而不是之后添加 0：

<?php 

function alter_brightness($colourstr, $steps) {
  $colourstr = str_replace('#','',$colourstr);

  $rhex = substr($colourstr,0,2);
  $ghex = substr($colourstr,2,2);
  $bhex = substr($colourstr,4,2);

  $r = hexdec($rhex);
  $g = hexdec($ghex);
  $b = hexdec($bhex);

  $r = dechex(max(0,min(255,$r + $steps)));
  $g = dechex(max(0,min(255,$g + $steps)));  
  $b = dechex(max(0,min(255,$b + $steps)));

  $r = str_pad($r,2,"0",STR_PAD_LEFT);
  $g = str_pad($g,2,"0",STR_PAD_LEFT);
  $b = str_pad($b,2,"0",STR_PAD_LEFT);

  $cor = '#'.$r.$g.$b;

  return $cor;
}

?>

Answer 3

<?php 

function alter_brightness($colourstr, $steps) {
  $colourstr = str_replace('#','',$colourstr);

  $rhex = substr($colourstr,0,2);
  $ghex = substr($colourstr,2,2);
  $bhex = substr($colourstr,4,2);

  $r = hexdec($rhex);
  $g = hexdec($ghex);
  $b = hexdec($bhex);

  $r = dechex(max(0,min(255,$r + $steps)));
  $g = dechex(max(0,min(255,$g + $steps)));  
  $b = dechex(max(0,min(255,$b + $steps)));

  $r = str_pad($r,2,"0");
  $g = str_pad($g,2,"0");
  $b = str_pad($b,2,"0");

  $cor = '#'.$r.$g.$b;

  return $cor;
}

?>

Answer 4

使用第二个答案。或将以下内容添加到您的代码中：

如果 rgb 值为 10 左右，它将返回十六进制的单个字符。它需要以 0 为前缀才能正确渲染。

  $newhex = '#';
  $newhex .= (strlen(dechex($r)) === 1) ?  '0'.dechex($r) : dechex($r);
  $newhex .= (strlen(dechex($g)) === 1) ?  '0'.dechex($g) : dechex($g);
  $newhex .= (strlen(dechex($b)) === 1) ?  '0'.dechex($b) : dechex($b);

  return $newhex;

Answer 5

这是该函数的缩小版本。我使用 str_pad 为数字 添加 0 10. cusimar9版本不检查这一点。

 function alter_brightness($colourstr, $steps) {
    //Take off the #
    $colourstr    = str_replace( '#', '', $colourstr );
    // Steps should be between -255 and 255. Negative = darker, positive = lighter
    $steps  = max( -255, min( 255, $steps ) );
    // Transform colors of type #fff to #ffffff
    if ( 3 == strlen( $colourstr ) ) {
        $colourstr    = str_repeat( substr( $colourstr, 0, 1 ), 2 ) . str_repeat( substr( $colourstr, 1, 1 ), 2 ) . str_repeat( substr( $colourstr, 2, 1 ), 2 );
    }
    // Modify the brigthness of each component
    $rgb=array(substr($colourstr,0,2),  substr($colourstr,2,2), substr($colourstr,4,2));
    for($i = 0; $i< count($rgb); $i++){
      $rgb[$i] = str_pad(dechex(max(0,min(255, hexdec($rgb[$i]) + $steps))),2,"0",STR_PAD_LEFT) ;
    }
    return '#'.implode('', $rgb);
}