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ImagickPixel::getColorValue

(PECL imagick 2, PECL imagick 3)

ImagickPixel::getColorValue — Gets the normalized value of the provided color channel

说明

public ImagickPixel::getColorValue(int $color): float

Retrieves the value of the color channel specified, as a floating-point number between 0 and 1.

参数

color: The color to get the value of, specified as one of the Imagick color constants. This can be one of the RGB colors, CMYK colors, alpha and opacity e.g (Imagick::COLOR_BLUE, Imagick::COLOR_MAGENTA).

返回值

The value of the channel, as a normalized floating-point number, throwing ImagickPixelException on error.

示例

示例 #1 Basic Imagick::getColorValue() usage

<?php
    
$color = new ImagickPixel('rgba(90%, 20%, 20%, 0.75)');

echo "Alpha value is ".$color->getColorValue(Imagick::COLOR_ALPHA).PHP_EOL;
echo "".PHP_EOL;
echo "Red value is ".$color->getColorValue(Imagick::COLOR_RED).PHP_EOL;
echo "Green value is ".$color->getColorValue(Imagick::COLOR_GREEN).PHP_EOL;
echo "Blue value is ".$color->getColorValue(Imagick::COLOR_BLUE).PHP_EOL;
echo "".PHP_EOL;
echo "Cyan value is ".$color->getColorValue(Imagick::COLOR_CYAN).PHP_EOL;
echo "Magenta value is ".$color->getColorValue(Imagick::COLOR_MAGENTA).PHP_EOL;
echo "Yellow value is ".$color->getColorValue(Imagick::COLOR_YELLOW).PHP_EOL;
echo "Black value is ".$color->getColorValue(Imagick::COLOR_BLACK).PHP_EOL;

?>

以上示例会输出：

 
Alpha value is 0.74999618524453

Red value is 0.90000762951095
Green value is 0.2
Blue value is 0.2

Cyan value is 0.90000762951095
Magenta value is 0.2
Yellow value is 0.2
Black value is 0

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User Contributed Notes 3 notes

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Anonymous ¶

3 years ago

COLOR_ALPHA - not fully transparent pixel
COLOR_OPACITY - completely transparent pixel

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holdoffhunger at gmail dot com ¶

11 years ago

When 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

    */

?>

down

mwwaygoo AT hotmail DOT com ¶

13 years ago

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);
?>

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