COLOR_ALPHA - not fully transparent pixel
COLOR_OPACITY - completely transparent pixel
(PECL imagick 2, PECL imagick 3)
ImagickPixel::getColorValue — Obtém o valor normalizado do canal de cores fornecido
Recupera o valor do canal de cores especificado, como um número de ponto flutuante entre 0 e 1.
colorA cor cujo valor será obtido, especificada como uma das constantes de cor do Imagick. Pode ser uma das cores RGB, cores CMYK, alfa e opacidade, por exemplo (Imagick::COLOR_BLUE, Imagick::COLOR_MAGENTA).
O valor do canal, como um número de ponto flutuante normalizado, lançando uma ImagickPixelException em caso de erro.
Exemplo #1 Uso básico de Imagick::getColorValue()
<?php
$color = new ImagickPixel('rgba(90%, 20%, 20%, 0.75)');
echo "Valor de alfa é ".$color->getColorValue(Imagick::COLOR_ALPHA).PHP_EOL;
echo "".PHP_EOL;
echo "Valor de vermelho é ".$color->getColorValue(Imagick::COLOR_RED).PHP_EOL;
echo "Valor de verde é ".$color->getColorValue(Imagick::COLOR_GREEN).PHP_EOL;
echo "Valor de azul é ".$color->getColorValue(Imagick::COLOR_BLUE).PHP_EOL;
echo "".PHP_EOL;
echo "Valor de ciano é ".$color->getColorValue(Imagick::COLOR_CYAN).PHP_EOL;
echo "Valor de magenta é ".$color->getColorValue(Imagick::COLOR_MAGENTA).PHP_EOL;
echo "Valor de amarelo é ".$color->getColorValue(Imagick::COLOR_YELLOW).PHP_EOL;
echo "Valor de preto é ".$color->getColorValue(Imagick::COLOR_BLACK).PHP_EOL;
?>O exemplo acima produzirá:
Valor de alfa é 0.74999618524453 Valor de vermelho é 0.90000762951095 Valor de verde é 0.2 Valor de azul é 0.2 Valor de ciano é 0.90000762951095 Valor de magenta é 0.2 Valor de amarelo é 0.2 Valor de preto é 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);
?>