classes/handlers/magick.php
public function brightness( $value, $region = null )
    {
        if ( $value < - 255 || $value > 255 )
        {
            throw new ezcBaseValueException( 'value', $value, 'int >= -255 && int <= 255' );
        }
        // 0 = -255
        // 50 = half as bright = -127
        // 100 = regular brightness = 0
        // 150 = 127
        // 200 = twice as bright = 255
        $value = ( 200 * ( $value + 255 ) ) / 512;

        $this->setRegion( $region );
        $this->addFilterOption( $this->getActiveReference(),
            '-modulate',
            $value
        );
    }
public function brightness( $value, $region = null )
    {
        if ( $value < - 255 || $value > 255 )
        {
            throw new ezcBaseValueException( 'value', $value, 'int >= -255 && int <= 255' );
        }
        // 0 = -255
        // 50 = half as bright = -127
        // 100 = regular brightness = 0
        // 150 = 127
        // 200 = twice as bright = 255
        $value = ( 200 * ( $value + 255 ) ) / 512;

        $this->setRegion( $region );
        $this->addFilterOption( $this->getActiveReference(),
            '-modulate',
            $value
        );
    }
/* (non-PHPdoc)
@see extension/ezie/autoloads/eziezc/interfaces/eZIEEzcConversions#brightness($value)