imagecolorsforindex()

(PHP 4, PHP 5, PHP 7)

取得某索引的颜色

说明

本函数返回一个具有 red，green，blue 和 alpha 的键名的关联数组，包含了指定颜色索引的相应的值。

imagecolorsforindex()例子

本例将输出：

Array
(
    [red] => 226
    [green] => 222
    [blue] => 252
    [alpha] => 0
)

参见imagecolorat()和imagecolorexact()。

Be aware that
 
will only work for truecolor images. With eg GIF images, this will have strange results. For GIF images, you should always use imagecolorsforindex().

I have optimized the rgb2hsl function from slepichev a bit, so that it is a bit shorter and hopefully a bit faster: 

While it's quite easy and intuitive to get the alpha transparency of a pixel with:

you should use the return value of the command imagecolorat to get the alpha transparency with the code below because it's much faster and will have a major impact if you process every pixel of an image: 

If you would like to change the intensity or lightness level of a specific color, you will need to convert the color format from RGB to HSL. 
following function convert RGB array(red,green,blue) to HSL array(hue, saturation, lightness) 

The earlier microsoft sepia example seemed to have a factor in which made it pinky... here is a modified example which uses just the Microsoft sepia (as per the wiki sepia entry) 

To correct m4551 at abasoft dot it example:
ImageTrueColorToPalette($im,1,$t);
might give less colors than $t, so the for loop should call "$i

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