Imagick::evaluateImage

    (PECL imagick 2, PECL imagick 3)

    Imagick::evaluateImage — Applies an expression to an image

    Description

    public Imagick::evaluateImage(int $op, float $constant, int $channel = Imagick::CHANNEL_DEFAULT): bool

    Applys an arithmetic, relational, or logical expression to an image. Use these operators to lighten or darken an image, to increase or decrease contrast in an image, or to produce the "negative" of an image.

    Parameters

    op

    The evaluation operator

    constant

    The value of the operator

    channel

    Provide any channel constant that is valid for your channel mode. To apply to more than one channel, combine channeltype constants using bitwise operators. Refer to this list of channel constants.

    Return Values

    Returns true on success.

    Errors/Exceptions

    Throws ImagickException on error.

    Examples

    Example #1 Using Imagick::evaluateImage()

    Using evaluateImage to reduce opacity in an image.

    <?php
    // Create new object with the image
    $im = new Imagick('example-alpha.png');

    // Reduce the alpha by 50%
    $im->evaluateImage(Imagick::EVALUATE_DIVIDE, 2, Imagick::CHANNEL_ALPHA);

    // Output the image
    header("Content-Type: image/png");
    echo     $im;
    ?>

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    User Contributed Notes 1 note

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    nils dot rocine at gmail dot com
    12 years ago
    What worked for me to convert a JPG source file to a semi-transparent PNG.

    <?php
    $srcImagick     = new Imagick($srcPath);

    $pathTo50Perc = 'transparent1.png';

    $srcImagick->setImageAlphaChannel(Imagick::ALPHACHANNEL_OPAQUE);

    $srcImagick->evaluateImage(Imagick::EVALUATE_DIVIDE, 2, Imagick::CHANNEL_ALPHA);

    $srcImagick->writeImage($pathTo50Perc);
    ?>
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