The Gmagick::equalizeimage() function is an inbuilt function in PHP which is used to equalizes the histogram of an image.
Syntax: 
Gmagick Gmagick::equalizeimage( void )
Parameters: This function does not accepts any parameter.
Return Value: This function returns equalized Gmagick object.
Errors/Exceptions: This function throws GmagickException on error.
Below programs illustrate the Gmagick::equalizeimage() function in PHP:
Program 1:
Original Image: 
 
PHP
<?php    // Create a Gmagick object $gmagick = new Gmagick(// Equalize the image.$gmagick->equalizeimage();header('Content-type: image/png');    // Output the image echo $gmagick; ?> | 
Output: 
 
Program 2:
PHP
<?php     // Create a GmagickDraw object $draw = new GmagickDraw();    // Create GmagickPixel object $strokeColor = new GmagickPixel('Red'); $fillColor = new GmagickPixel('Green');    // Set the color, opacity of image $draw->setStrokeOpacity(1); $draw->setStrokeColor('Red'); $draw->setFillColor('Green');    // Set the width and height of image $draw->setStrokeWidth(7); $draw->setFontSize(72);     // Function to draw circle  $draw->circle(250, 250, 100, 150);   $gmagick = new Gmagick(); $gmagick->newImage(500, 500, 'White'); $gmagick->setImageFormat("png"); $gmagick->drawImage($draw); // Equalize the image$gmagick->equalizeimage();  // Display the output image header("Content-Type: image/png"); echo $gmagick->getImageBlob(); ?>  | 
Output: 
 
Reference: http://php.net/manual/en/gmagick.equalizeimage.php
 

                                    