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GD Thumbnail Based On Image Type

To create a thumbnail image based on the image type with GD is quite simple give a few key functions. The magic here is done by using the function imagecreatefromstring() instead of imagecreatefromjpeg() and other similar functions for other image formats.

The imagecreatefromstring() is not dependant on file type so any image type can be read into the script and a thumbnail canvas created and then the image string is "mapped" onto the thumbnail canvas with imagecreatetruecolor().

This example also provides variables for setting the thumbnail height to make galleries nice and tidy and also a variable for the thumbnail prefix. This allows the user to prepend an identifier for the thumbnail image. It can also be set to an empty string if it is not required.

The thumbnail filename itself is automatically generated from the original filename and the aspect ratio is also maintained with the use some simple math.

Finally the file is written to disk with the use of imagejpeg(), imagepng)(), imagegif(), or imagewbmp() depending on the file type. Some further checks could be added to make sure the permissions are correct to write the file, or perhaps a check to see if the file aready exists. These tasks are left to the user to decide.


<?php

    error_reporting(E_ALL);

    /*** the source image file to thumbnail ***/
    $source_image = 'spork.jpg';

    /*** maximum height ***/
    $thumb_height = 40;

    /*** thumb prefix ***/
    $thumb_prefix = 'thumb_';

    /*** the thumbnail quality ***/
    $quality = 100;

    /*** check if the file exists ***/
    if(!file_exists($source_image))
    {
        echo 'No file found';
    }
    else
    {
        /*** supported types ***/
        $supported_types = array(1, 2, 3, 7);

        /*** get the image info ***/
        list($width_orig, $height_orig, $image_type) = getimagesize($source_image);

        /** check for supported type ***/
        if(!in_array($image_type, $supported_types))
        {
            echo 'Unsupported Image Type: ' . $image_type;
        }
        else
        {

            /*** get the filename ***/
            $path_parts = pathinfo($source_image);
            $filename = $path_parts['filename'];

            /*** calculate the aspect ratio ***/
            $aspect_ratio = (float) $width_orig / $height_orig;

            /*** calulate the thumbnail width based on the height ***/
            $thumb_width = round($thumb_height * $aspect_ratio);
 
            /*** imagecreatefromstring will automatically detect the file type ***/
            $source = imagecreatefromstring(file_get_contents($source_image));

            /*** create the thumbnail canvas ***/ 
            $thumb = imagecreatetruecolor($thumb_width, $thumb_height);

            /*** map the image to the thumbnail ***/
            imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumb_width, $thumb_height, $width_orig, $height_orig);
            /*** destroy the source ***/
            imagedestroy($source);
 
            /*** write thumbnail based on file type ***/
            switch ( $image_type )
            {
                case 1:
                    imagegif($im, $fileName);
                    $thumbnail = $thumb_prefix.$filename . '.gif';
                    break;

                case 2:
                    $thumbnail = $thumb_prefix.$filename . '.jpg';
                    imagejpeg($thumb, $thumbnail, $quality);
                    break;

                case 3:
                    imagepng($im, $fileName);
                    $thumbnail = $thumb_prefix.$filename . '.png';
                    break;

                case 7:
                    imagewbmp($im, $fileName);
                    $thumbnail = $thumb_prefix.$filename . '.bmp';
                    break;
            }
        }
    }
?>