PHP将24位颜色转换为4位 [英] PHP convert 24-bit colors to 4-bit

问题描述

背景，我将图像转换为ascii艺术。这工作完美，甚至工程与24位颜色，将颜色转换为正确的rgb值。然而，我现在想要渲染ascii艺术在4位调色板而不是24位。

如何将24位颜色转换为4位PHP？

更具体地说，我有标准的IRC颜色托盘，我需要转换任何给定的十六进制或RGB值。

其他的想法，我已经在这是将图像本身转换为一个4位调色板（使用GD，这是我现在使用的颜色读取），然后试图抓住它的颜色。另一个想法可能是为每个下面的颜色定义一个颜色范围，只是检查给定的24位颜色是否在范围内，但是我不知道如何获得所有颜色的范围到该调色板。 / p>

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解决方案

最后，尽管围绕imagemagick的精彩建议，我发现了一个很好的解决方案使用直php。我能够通过使用delta E 2000与github上找到的php-color-difference库的修改版本来计算最接近的颜色，这里是我的fork： https://github.com/nalipaz/php-color-difference

相关示例是：

 <？php 
 include（'lib / color_difference.class.php'）; 
 
 $ palette = array（
'00'=> array（255，255，255），
'01'=& ，
'02'=> array（0,0,139），
'03'=> array（0，128，0），
'04'=& （255,0,0），
'05'=>数组（139,0,0），
'06'=> array（128,0,128），
 '07'=> array（255,165,0），
'08'=> array（255，255，0），
'09'=& 50），
'10'=>数组（0,128,128），
'11'=> array（173,216,230），
'12'=> ; array（0,0,255），
'13'=> array（255，105，180），
'14'=& $ b'15'=> array（211，211，211），
）; 
 
 $ color_rgb = array（255，255，128）; 
 $ color_delta_e = new color_difference（$ color_rgb）; 
 $ match_index = $ color_delta_e-> getClosestMatch（$ palette）; 
 $ color = $ palette [$ match_index]; 
  

我对这个解决方案感到非常满意，感谢您的建议。

Background, I am converting images to ascii art. This works perfectly and even works with 24-bit color, converting the colors to the right rgb values. However, I now want to render the ascii art in 4-bit color palette rather than 24-bit.

How do I convert 24-bit colors to 4-bit with PHP?

More specifically, I have the standard IRC color pallet which I need to convert any given Hexidecimal or RGB value to. It is preferred that the colors match as best as possible when converted to the 4-bit color.

Other ideas I have had on this are to convert the image itself to a 4-bit palette (using GD, which is what I use to read in the colors right now) before trying to grab colors off of it. And another idea might be to define a color range for each of the following color and just check that the given 24-bit color is in the range, however I wouldn't know how to get the ranges for all colors into that palette.

解决方案

In the end, despite the wonderful suggestions surrounding imagemagick I found a good solution using straight php. I was able to calculate the closest color through the use of delta E 2000 with a modified version of php-color-difference library found on github, here is my fork: https://github.com/nalipaz/php-color-difference

The pertinent example is:

<?php
include('lib/color_difference.class.php');

$palette = array(
  '00' => array(255, 255, 255),
  '01' => array(0, 0, 0),
  '02' => array(0, 0, 139),
  '03' => array(0, 128, 0),
  '04' => array(255, 0, 0),
  '05' => array(139, 0, 0),
  '06' => array(128, 0, 128),
  '07' => array(255, 165, 0),
  '08' => array(255, 255, 0),
  '09' => array(50, 205, 50),
  '10' => array(0, 128, 128),
  '11' => array(173, 216, 230),
  '12' => array(0, 0, 255),
  '13' => array(255, 105, 180),
  '14' => array(128, 128, 128),
  '15' => array(211, 211, 211),
);

$color_rgb = array(255, 255, 128);
$color_delta_e = new color_difference($color_rgb);
$match_index = $color_delta_e->getClosestMatch($palette);
$color = $palette[$match_index];

I am pretty happy with this solution and smaller amount of overhead. Thanks for the suggestions guys.

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