COLOR_ALPHA - not fully transparent pixel
COLOR_OPACITY - completely transparent pixel
(PECL imagick 2, PECL imagick 3)
ImagickPixel::getColorValue — Récupère la valeur normalisée du canal de la couleur fournie
Récupère la valeur du canal de la couleur spécifiée, sous la forme d'un nombre à virgule flottante compris entre 0 et 1.
colorLa couleur pour laquelle la valeur sera récupérée, spécifiée sous forme de constante de couleurs Imagick. Peut être des couleurs RGB, des couleurs CMYK, alpha et opacité, i.e. Imagick::COLOR_BLUE ou Imagick::COLOR_MAGENTA.
La valeur du canal, sous la forme d'un nombre à virgule flottante normalisé, ou lance une exception ImagickPixelException si une erreur survient.
Exemple #1 Utilisation basique de la méthode Imagick::getColorValue()
<?php
$color = new ImagickPixel('rgba(90%, 20%, 20%, 0.75)');
echo "La valeur alpha est ".$color->getColorValue(Imagick::COLOR_ALPHA).PHP_EOL;
echo "".PHP_EOL;
echo "La valeur rouge est ".$color->getColorValue(Imagick::COLOR_RED).PHP_EOL;
echo "La valeur verte est ".$color->getColorValue(Imagick::COLOR_GREEN).PHP_EOL;
echo "La valeur bleue est ".$color->getColorValue(Imagick::COLOR_BLUE).PHP_EOL;
echo "".PHP_EOL;
echo "La valeur Cyan est ".$color->getColorValue(Imagick::COLOR_CYAN).PHP_EOL;
echo "La valeur Magenta est ".$color->getColorValue(Imagick::COLOR_MAGENTA).PHP_EOL;
echo "La valeur jaune est ".$color->getColorValue(Imagick::COLOR_YELLOW).PHP_EOL;
echo "La valeur noire est ".$color->getColorValue(Imagick::COLOR_BLACK).PHP_EOL;
?>L'exemple ci-dessus va afficher :
La valeur alpha est 0.74999618524453 La valeur rouge est 0.90000762951095 La valeur verte est 0.2 La valeur bleue est 0.2 La valeur Cyan est 0.90000762951095 La valeur Magenta est 0.2 La valeur jaune est 0.2 La valeur noire est 0
COLOR_ALPHA - not fully transparent pixel
COLOR_OPACITY - completely transparent pixelWhen getting a color value back with getColorValue, you are free to use any color scheme: either the Red/Green/Blue (RGB) scheme or the Cyan/Magenta/Yellow/blacK (CMYK) scheme. For RGB, this function works with the constant values of "COLOR_RED", "COLOR_GREEN", and "COLOR_BLUE," and for CMYK, this function works with the constant values of "COLOR_CYAN", "COLOR_MAGENTA", "COLOR_YELLOW", and "COLOR_BLACK". As a programmer, the main question you're probably asking yourself is "How do I know if one pixel's color is different from the others?" That seems to be defined as a unique combination of RGB *or* CMYK values. Each RGB set of values with have a unique set of CMYK values for only that set of RGB values, so an RGB of 1/0.5/0.5 with have a unique set of CMYK values, shared only by the other pixels of the same exact RGB values.
Why the CMYK? Because that is the standard for printing, or to quote the Imagick site, "As such for printing we use four colored inks: Cyan, Magenta, Yellow, and blacK; and define images using these inks, to form a CMYK color space." By being a "color space", you get the choice of working with either RGB or CMYK when defining a pixel as being unique among a set of pixels. But you are completely free to go with either RGB or CMYK. For more on it from the Imagick Site:
http://www.imagemagick.org/Usage/color_basics/
Some code that demonstrates both methods: (for a purple-ish red pixel)
<?php
// Grab Pixel
// ---------------------------------------------------
$pixel_one = $imagick_type->getImagePixelColor(0,0);
// Grab Alpha/Opacity Values
// ---------------------------------------------------
$pixel_one_color_value_alpha = $pixel_one->getColorValue(imagick::COLOR_ALPHA);
$pixel_one_color_value_opacity = $pixel_one->getColorValue(imagick::COLOR_OPACITY);
// Grab Red/Green/Blue (RGB) Values
// ---------------------------------------------------
$pixel_one_color_value_red = $pixel_one->getColorValue(imagick::COLOR_RED);
$pixel_one_color_value_green = $pixel_one->getColorValue(imagick::COLOR_GREEN);
$pixel_one_color_value_blue = $pixel_one->getColorValue(imagick::COLOR_BLUE);
// Grab Cyna/Magenta/Yellow/blacK (CMYK) Values
// ---------------------------------------------------
$pixel_one_color_value_cyan = $pixel_one->getColorValue(imagick::COLOR_CYAN);
$pixel_one_color_value_magenta = $pixel_one->getColorValue(imagick::COLOR_MAGENTA);
$pixel_one_color_value_yellow = $pixel_one->getColorValue(imagick::COLOR_YELLOW);
$pixel_one_color_value_black = $pixel_one->getColorValue(imagick::COLOR_BLACK);
// Print Results
// ---------------------------------------------------
print("Alpha: $pixel_one_color_value_alpha<br>");
print("Opacity: $pixel_one_color_value_opacity<br><br>");
print("---------------------------------------------<br><br>");
print("Red: $pixel_one_color_value_red<br>");
print("Green: $pixel_one_color_value_green<br>");
print("Blue: $pixel_one_color_value_blue<br><br>");
print("Cyan: $pixel_one_color_value_cyan<br>");
print("Magenta: $pixel_one_color_value_magenta<br>");
print("Yellow: $pixel_one_color_value_yellow<br>");
print("Black: $pixel_one_color_value_black<br><br>");
/*
Example Results : : :
-----------------------
Alpha: 1
Opacity: 0
---------------------------------------------
Red: 1
Green: 0.501960784314
Blue: 0.501960784314
Cyan: 1
Magenta: 0.501960784314
Yellow: 0.501960784314
Black: 0
*/
?>QUOTE: $color The channel to check, specified as one of the Imagick channel constants.
$color is a COLOR_* constant, not a channel constant
e.g.
<?php
$image=new Imagick();
$image->readImage('test.png');
$point=$image->getImagePixelColor(0,0);
echo ' Alpha:'.$point->getColorValue(imagick::COLOR_ALPHA);
echo ' Opacity:'.$point->getColorValue(imagick::COLOR_OPACITY);
echo ' R:'.$point->getColorValue(imagick::COLOR_RED);
echo ' G:'.$point->getColorValue(imagick::COLOR_GREEN);
echo ' B:'.$point->getColorValue(imagick::COLOR_BLUE);
?>