Approaches to Web Development for Bioinformatics

Medical Computing > Web Development for Bioinformatics > Web Development > PHP > Images

Image Generation

PHP scripts can generate images using the GD library. This is a built in extension but is not enabled by default. To enable it in the make sure the line

PHP Configuration File

extension=php_gd2.dll

or equivalent unix shared library is present in the php.ini file. The PHP manual ³⁵ gives details on the use of the GD library with PHP. The PHP functions wrap the C-based GD library. More information on the GD project can be found at the libgd site ⁷¹.

Here is a program that creates a simple rectangle and then outputs it to the browser as a PNG image.

PHP

<?php

// Program to demonstrate use of GD graphics library

// Create a rectangle
$image = ImageCreate(200, 100);
$backgroundColor = ImageColorAllocate($image, 255, 255, 255);
$red = ImageColorAllocate($image, 255, 0, 0);
ImageFilledRectangle($image, 50, 50, 150, 100, $red);

// Output the image
header('Content-Type: image/png');
ImagePNG($image);

The program first creates an image object with the ImageCreate($width, $height) call. Then it allocates objects for the colors white and red with the function ImageColorAllocate($image, $r, $g, $b). A red rectangle is drawn on the image with the call ImageFilledRectangle($image, $x1, $y1, $x2, $y2, $color). All the units are pixels and the coordinate origin is at the top left. A header is written to let the browswer know to expect a PNG MIME type. Finally, the image is written to the browswer with the call ImagePNG($image). The image generated looks like this.

Screenshot of Basic PHP Image Generation Script for Script Above

Open rectangles can be drawn with the ImageRectangle($image, $x1, $y1, $x2, $y2, $color) function and lines can be drawn with the function ImageLine($image, $x1, $y1, $x2, $y2, $color). This is demonstrated in the script test_gd_line.phps. The program output is shown below:

Screenshot of Basic PHP Image Generation Script

(test_gd_line.phps)

You can draw text on images with the ImageString($image, $fontSize, $x, $y, $text, $color) function. The program test_gd_text.phps demonstrates this. The image generated is shown below.

Screenshot of Basic PHP Image Generation Script

(test_gd_text.phps)

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