How to manipulate images and work with GD library in php

How to manipulate images and work with GD library in PHP

Graphics are used to make a website more beautiful and you can use many tools like Adobe Photoshop for that but in a lot of places, we need dynamic image manipulation. For this purpose, we can use GD library in PHP. In this article, you will learn how to manipulate images and work with GD library in PHP. You can open, save or draw images on a canvas, create a thumbnail of a large image or can add watermark and many other effects.

Colors theory and coordinate system

Before working in GD library let us explore colors theory and coordinate system. The computer is the world of colors. As you have seen many color monitors. The computer uses a Color Theory Model that is called RGB or red, green, blue. A computer creates colors by using these basic colors.

Co-ordinate System

 

Generating images

Generating a new image

$image = imagecreate(200, 150);

Allocate color to images

int imagecolorallocate ( resource $image , int $red , int $green , int $blue )

$red    = imagecolorallocate($image, 255, 0, 0);

$white  = imagecolorallocate($image, 255, 255, 255);

$black  = imagecolorallocate($image, 0, 0, 0);

$white = imagecolorallocate($image, 0xFF, 0xFF, 0xFF);

$black = imagecolorallocate($image, 0x00, 0x00, 0x00);

Basics  of drawing with GD library in PHP

How to draw a pixel on an image.

$canvas     = imagecreate(200, 100)

$grey       = imagecolorallocate($canvas, 230, 230, 230);

$black      = imagecolorallocate($canvas, 0, 0, 0);

imagesetpixel($canvas, 120, 60, $black)
 
header("Content-type: image/png");

imagepng($cnavas)

imagedestroy($canvas);

We created a blank canvas using imagecreate function and storing in $canvas whose width is 200 X 100. Two colors grey and black using imagecolorallocate with parameters $canvas and Red, Green, Blue color values. imagesetpixel method accepts 4 parameters,  first argument is  $canvas variable, then x, y co-ordinates and last argument is color.

A pixel is created on canvas  on 120px from x-axis of left side and 60px from y-axis. Next is the header function that sends image contents to the browser as a PNG image. In order to save this image on hard disk, we can pass image path as an optional argument.

imagepng('/images/pixel.png');

How to draw line using GD library in php

bool imageline ( resource $image , int $x1 , int $y1 , int $x2 , int $y2 , int $color )

//Create a 200 x 200 image
$canvas = imagecreatetruecolor(200, 200);

//Allocate color
$green = imagecolorallocate($canvas, 132, 135, 28);

//Draw line each with its own color
imageline($canvas, 60, 60, 120, 120, $green);

//Output image and free from memory
header('Content-Type: image/jpeg');

imagejpeg($canvas);

imagedestroy($canvas);

How to create a rectangle using GD library in PHP

bool imagerectangle ( resource $image , int $x1 , int $y1 , int $x2 , int $y2 , int $color )

// Create a 200 x 200 image
$canvas = imagecreatetruecolor(200, 200);

// Allocate color
$white = imagecolorallocate($canvas, 255, 255, 255);

// Draw rectangle each with its color
imagerectangle($canvas, 45, 60, 120, 100, $white);

// Output and free from memory

header('Content-Type: image/jpeg');

imagejpeg($canvas);

imagedestroy($canvas);

How to create a circle and ellipses using GD library in PHP

bool imageellipse ( resource $image , int $cx , int $cy , int $width , int $height , int $color )

//Create a blank image.
$image = imagecreatetruecolor(400, 300);

//Choose a color for the ellipse.

$color = imagecolorallocate($image, 255, 255, 255);

//Draw the ellipse.

imageellipse($image, 200, 150, 300, 200, $color);

//Output the image.

header("Content-type: image/png");

imagepng($image);

Create Circle using GD library in php

In order to create a complete Circle we need to specify the same height and width like

 // Draw the circle.
imageellipse($image, 200, 150, 200, 200, $color);

Code to draw a complete circle.

// Create a blank image.

$image = imagecreatetruecolor(400, 300);


// Choose a color for the ellipse.

$color = imagecolorallocate($image, 255, 255, 255);


// Draw the ellipse.

imageellipse($image, 200, 150, 200, 200, $color);


// Output the image.

header("Content-type: image/png");
imagepng($image);

How to draw an arc using GD Library in PHP

bool imagearc (resource $image, int $cx,int $cy, int $width, int $height, int $start,int $end,int $color )

// create a 1500*150 image
$image     = imagecreatetruecolor(200, 200);

// allocate some colors
$white   = imagecolorallocate($image, 255, 255, 255);

$red     = imagecolorallocate($image, 255,   0,   0);

$green   = imagecolorallocate($image,   0, 255,   0);

$blue    = imagecolorallocate($image,   0,   0, 255);
 
// draw the head
imagearc($image, 100, 100, 200, 200,  0, 360, $white);

// draw mouth
imagearc($image, 100, 100, 150, 150, 25, 155, $red);

// left and then the right eye
imagearc($image,  60,  75,  50,  50,  0, 360, $green);

imagearc($image, 140,  75,  50,  50,  0, 360, $blue);
 
// output image in the browser
header("Content-type: image/png");

imagepng($image);
 
// free memory
imagedestroy($image);

How to create polygons using PHP GD library

bool imagepolygon ( resource $image , array $points , int $num_points , int $color )

// Create a blank image
$image = imagecreatetruecolor(400, 300);
 
// Allocate a color for the polygon
$color = imagecolorallocate($image, 255, 255, 255);
 
// Draw the polygon
imagepolygon($image, array(
        0,   0,
        100, 200,
        300, 200
    ),
    3,
    $color);
 
// Output the picture to the browser
header('Content-type: image/png');
 
imagepng($image);

imagedestroy($image);

In order to do this you have  to create an image resource using imagecreatetruecolor, then allocated black color to $color using imagecolorallocate function. In addition inimagepolygon parameters passed are $image as image resource and an array of vertices.

The first vertex is x, y as 0, 0 second vertex is 100, 200 and third vertex is 300, 200, then we specify the number of vertices. The last argument is $color. This creates a polygon as shown above.

How to create a thumbnail using GD library in PHP

Generate Thumbnail using GD library in PHP

 $image 		    = imagecreatefromjpeg('flower.jpeg');
 
 $width 		    = imagesx($image);
 
 $height 	 	    = imagesy($image);
 
 $thumb_height              = intval($height / 3);
 
 $thumb_width               = intval($width / 3);
  
 $thumbnail 	            = imagecreatetruecolor($thumb_width, $thumb_height);
  
 imagecopyresampled($thumbnail, $image, 0,0,0,0, $thumb_width, $thumb_height, $width, $height);
  
 header('content-type: image/jpeg');
  
 imagejpeg($thumbnail);
  
 imagedestroy($thumbnail);

 imagedestroy($image);

Summary

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• Watermark images using php

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