Imagick::getImageHistogram

(PECL imagick 2.0.0)

Imagick::getImageHistogram — Gets the image histogram

说明

array Imagick::getImageHistogram ( void )

Returns the image histogram as an array of ImagickPixel objects.

返回值

Returns the image histogram as an array of ImagickPixel objects.

错误／异常

错误时抛出 ImagickException。

范例

Example #1 Generates Imagick::getImageHistogram()

  <?php
 function  getColorStatistics ( $histogramElements ,  $colorChannel ) {
     $colorStatistics  = [];

    foreach ( $histogramElements  as  $histogramElement ) {
         $color  =  $histogramElement -> getColorValue ( $colorChannel );
         $color  =  intval ( $color  *  255 );
         $count  =  $histogramElement -> getColorCount ();

        if ( array_key_exists ( $color ,  $colorStatistics )) {
             $colorStatistics [ $color ] +=  $count ;
        }
        else {
             $colorStatistics [ $color ] =  $count ;
        }
    }

     ksort ( $colorStatistics );
    
    return  $colorStatistics ;
}
    


function  getImageHistogram ( $imagePath ) {

     $backgroundColor  =  'black' ;

     $draw  = new \ ImagickDraw ();
     $draw -> setStrokeWidth ( 0 );  //make the lines be as thin as possible

     $imagick  = new \ Imagick ();
     $imagick -> newImage ( 500 ,  500 ,  $backgroundColor );
     $imagick -> setImageFormat ( "png" );
     $imagick -> drawImage ( $draw );

     $histogramWidth  =  256 ;
     $histogramHeight  =  100 ;  // the height for each RGB segment

     $imagick  = new \ Imagick ( realpath ( $imagePath ));
     //Resize the image to be small, otherwise PHP tends to run out of memory
    //This might lead to bad results for images that are pathologically 'pixelly'
     $imagick -> adaptiveResizeImage ( 200 ,  200 ,  true );
     $histogramElements  =  $imagick -> getImageHistogram ();

     $histogram  = new \ Imagick ();
     $histogram -> newpseudoimage ( $histogramWidth ,  $histogramHeight  *  3 ,  'xc:black' );
     $histogram -> setImageFormat ( 'png' );

     $getMax  = function ( $carry ,  $item )  {
        if ( $item  >  $carry ) {
            return  $item ;
        }
        return  $carry ;
    };

     $colorValues  = [
         'red'  =>  getColorStatistics ( $histogramElements , \ Imagick :: COLOR_RED ),
         'lime'  =>  getColorStatistics ( $histogramElements , \ Imagick :: COLOR_GREEN ),
         'blue'  =>  getColorStatistics ( $histogramElements , \ Imagick :: COLOR_BLUE ),
    ];

     $max  =  array_reduce ( $colorValues [ 'red' ] ,  $getMax ,  0 );
     $max  =  array_reduce ( $colorValues [ 'lime' ] ,  $getMax ,  $max );
     $max  =  array_reduce ( $colorValues [ 'blue' ] ,  $getMax ,  $max );

     $scale  =   $histogramHeight  /  $max ;

     $count  =  0 ;
    foreach ( $colorValues  as  $color  =>  $values ) {
         $draw -> setstrokecolor ( $color );

         $offset  = ( $count  +  1 ) *  $histogramHeight ;

        foreach ( $values  as  $index  =>  $value ) {
             $draw -> line ( $index ,  $offset ,  $index ,  $offset  - ( $value  *  $scale ));
        }
         $count ++;
    }

     $histogram -> drawImage ( $draw );
    
     header (  "Content-Type: image/png"  );
    echo  $histogram ;
}

 ?>

用户评论:

[#1] Iddles [2011-06-20 04:02:23]

Scratched my head for a while trying to figure out why this only returned a list of coloured pixels, and seemingly no colour count. Well it turns out that for some reason, the ImagickPixel class has a "getColorCount" method, which seems a strange place for it but hey.

<?php $image = new Imagick("thing.png"); $pixels=$image->getImageHistogram(); foreach($pixels as $p){ $colors = $p->getColor(); foreach($colors as $c){ print( "$c\t" ); } print( "\t:\t" . $p->getColorCount() . "\n" ); } ?>

This will print out something like:

252 250 252 1 : 125
194 156 182 1 : 126
109 18 79 1 : 11440
2 117 162 1 : 12761
255 255 255 1 : 40769

...where the colums are red, green, blue, alpha, followed by the number of times that colour appears in the image.