In case a package has to deal with colors, it is recommended that
developers store and use an array representation of the color values
in their PEAR packages. All values are in the range of 0..255.
The following snippet defines an array that holds the RGB
definition of the green coloring that is used in the official PEAR
$color = array(0x33, 0x99, 0x00);
$color = array(51, 153, 0);
Please note that the internal, numerical representation of both forms
of the example are equal. The values represent the RGB (red, green,
blue) values. It was decided not to use "r", "g" and "b" as indices
for the array, because numerical indices allow easier creation of
color arrays in the sourcecode, make handling less complicated and
are an already commonly used array representation for colors.
Since this an extension of the RGB representation above, it is
recommended to use a forth value for alpha-channel-prepresentation.
An example of the "PEAR-green" with aprox. 80%
intensity would be:
$color = array(0x33, 0x99, 0x00, 0xCC);
For consistency the alpha-value is also from the range 0..255. A
value of 255 means fully opaque (full color-intensity, same as in RGB-
notation), 0 means fully transparent.
Please note this is in contrast to the alpha-value used by
imagecolorallocate(). The alpha-representation used in PEAR was
choosen for consistency with the other RGB values and because it is
commonly accepted practise in many other applications
(image-processing tools, etc.).
Since RGB/RGBA will used for graphic generation on a computer we
decided to leave out an optional type-identifier classifying colors
as RGB/RGBA. However for different color-representations an
identifier is needed. The optional identifier "type" can be added to
the color array.
$color = array(0x33, 0x99, 0x00, 0xCC, "type" => "RGB");
Currently the following types are definied, with array-indices from
0..n follwing the colornames listed behind them:
Please note that also the RGBA representation has the type "RGB"
since it's closely related.
The PEAR-package Image_Color
will (hopefully soon) contain all needed functions to convert arbitrary
color formats to the internal RGBA representation and convert different
Status: Currently Image_Color already offers functions to convert
color-names (e.g. "green") and hex-representations-strings (e.g.
"#339900") to the PEAR-RGBA-format. We are working to get alpha-
channel support added hopefully soon and will later add funtions for
CYMK-conversion as well.