Create thumbnails with PHP

create-thumbnail.php

<?

// Link image type to correct image loader and saver
// - makes it easier to add additional types later on
// - makes the function easier to read
const IMAGE_HANDLERS = [
    IMAGETYPE_JPEG => [
        'load' => 'imagecreatefromjpeg',
        'save' => 'imagejpeg',
        'quality' => 100
    ],
    IMAGETYPE_PNG => [
        'load' => 'imagecreatefrompng',
        'save' => 'imagepng',
        'quality' => 0
    ],
    IMAGETYPE_GIF => [
        'load' => 'imagecreatefromgif',
        'save' => 'imagegif'
    ]
];

/**
 * @param $src - a valid file location
 * @param $dest - a valid file target
 * @param $targetWidth - desired output width
 * @param $targetHeight - desired output height or null
 */
function createThumbnail($src, $dest, $targetWidth, $targetHeight = null) {

    // 1. Load the image from the given $src
    // - see if the file actually exists
    // - check if it's of a valid image type
    // - load the image resource

    // get the type of the image
    // we need the type to determine the correct loader
    $type = exif_imagetype($src);

    // if no valid type or no handler found -> exit
    if (!$type || !IMAGE_HANDLERS[$type]) {
        return null;
    }

    // load the image with the correct loader
    $image = call_user_func(IMAGE_HANDLERS[$type]['load'], $src);

    // no image found at supplied location -> exit
    if (!$image) {
        return null;
    }


    // 2. Create a thumbnail and resize the loaded $image
    // - get the image dimensions
    // - define the output size appropriately
    // - create a thumbnail based on that size
    // - set alpha transparency for GIFs and PNGs
    // - draw the final thumbnail

    // get original image width and height
    $width = imagesx($image);
    $height = imagesy($image);

    // maintain aspect ratio when no height set
    if ($targetHeight == null) {

        // get width to height ratio
        $ratio = $width / $height;

        // if is portrait
        // use ratio to scale height to fit in square
        if ($width > $height) {
            $targetHeight = floor($targetWidth / $ratio);
        }
        // if is landscape
        // use ratio to scale width to fit in square
        else {
            $targetHeight = $targetWidth;
            $targetWidth = floor($targetWidth * $ratio);
        }
    }

    // create duplicate image based on calculated target size
    $thumbnail = imagecreatetruecolor($targetWidth, $targetHeight);

    // set transparency options for GIFs and PNGs
    if ($type == IMAGETYPE_GIF || $type == IMAGETYPE_PNG) {

        // make image transparent
        imagecolortransparent(
            $thumbnail,
            imagecolorallocate($thumbnail, 0, 0, 0)
        );

        // additional settings for PNGs
        if ($type == IMAGETYPE_PNG) {
            imagealphablending($thumbnail, false);
            imagesavealpha($thumbnail, true);
        }
    }

    // copy entire source image to duplicate image and resize
    imagecopyresampled(
        $thumbnail,
        $image,
        0, 0, 0, 0,
        $targetWidth, $targetHeight,
        $width, $height
    );


    // 3. Save the $thumbnail to disk
    // - call the correct save method
    // - set the correct quality level

    // save the duplicate version of the image to disk
    return call_user_func(
        IMAGE_HANDLERS[$type]['save'],
        $thumbnail,
        $dest,
        IMAGE_HANDLERS[$type]['quality']
    );
}

the imagegif() function does not have third parameter so after calling call_user_func() on a gif img an error occurs invalid index "quality"

After reducing the image, its size in bytes only grows.

it works !! awesome .

If you are trying to make a thumbnail of "gif" image and you are getting invalid index "quality", then go to line 17 and replace
IMAGETYPE_GIF => [ 'load' => 'imagecreatefromgif', 'save' => 'imagegif' ]

with

IMAGETYPE_GIF => [ 'load' => 'imagecreatefromgif', 'save' => 'imagegif', 'quality' => 0 ]

Example from effcore CMS/CMF (/system/module_core/backend/core.php):

namespace effcore {
          abstract class core {

  static function thumbnail_create($src_path, $dst_path, $dst_w = 100, $result_format = null) {
    $type = @exif_imagetype($src_path);
    if ($type !== false) {
      if ($type == IMAGETYPE_GIF  && function_exists('imagecreatefromgif' )) $src_resource = @imagecreatefromgif ($src_path);
      if ($type == IMAGETYPE_JPEG && function_exists('imagecreatefromjpeg')) $src_resource = @imagecreatefromjpeg($src_path);
      if ($type == IMAGETYPE_PNG  && function_exists('imagecreatefrompng' )) $src_resource = @imagecreatefrompng ($src_path);
      if (isset($src_resource) &&
                $src_resource) {
        $src_w = imagesx($src_resource);
        $src_h = imagesy($src_resource);
        $dst_h = (int)($src_h / ($src_w / $dst_w));
        $dst_resource = @imagecreatetruecolor($dst_w, $dst_h);
        @imagecolortransparent($dst_resource, imagecolorallocate($dst_resource, 0, 0, 0));
        @imagealphablending   ($dst_resource, $type == IMAGETYPE_GIF);
        @imagesavealpha       ($dst_resource, true);
        if ($dst_resource) {
          @imagecopyresampled($dst_resource, $src_resource, 0, 0, 0, 0, $dst_w, $dst_h, $src_w, $src_h);
          if ((($type == IMAGETYPE_PNG  && $result_format == null) || $result_format == 'png' ) && function_exists('imagepng' )) $result = @imagepng ($dst_resource, $dst_path.'.png' );
          if ((($type == IMAGETYPE_JPEG && $result_format == null) || $result_format == 'jpeg') && function_exists('imagejpeg')) $result = @imagejpeg($dst_resource, $dst_path.'.jpeg');
          if ((($type == IMAGETYPE_GIF  && $result_format == null) || $result_format == 'gif' ) && function_exists('imagegif' )) $result = @imagegif ($dst_resource, $dst_path.'.gif' );
          @imagedestroy($dst_resource);
          return $result ?? null;
        }
      }
    }
  }

 }}

Usage:

  core::thumbnail_create('/some_file.gif', '/some_file-thumb');
  core::thumbnail_create('/some_file.png', '/some_file-thumb');
  core::thumbnail_create('/some_file.jpg', '/some_file-thumb');

Thanks a lot for this!
On my page (https://www.pollisoft.se), is use the same thumbnail size for all image size and aspect ratios. With the following change/addition (the else statement) to your script, I avoided thumbnail image distortion when sourceRatio doesn't equal targetRatio. Feel free to include if you want.

`// maintain aspect ratio when no height set
if ($targetHeight == null) {

	$startX = 0;
	$startY = 0;
	$src_w = width;
	$src_h = height;
	
    // get width to height ratio
    $ratio = $width / $height;

    // if is portrait
    // use ratio to scale height to fit in square
    if ($width > $height) {
        $targetHeight = floor($targetWidth / $ratio);
    }
    // if is landscape
    // use ratio to scale width to fit in square
    else {
        $targetHeight = $targetWidth;
        $targetWidth = floor($targetWidth * $ratio);
    }
} else {
	// Calculate starting positions and copy area 
	// to not distort the thumbnail image ratio.
	// get width to height ratio
	$ratio = $width / $height;
	$targetRatio = $targetWidth / $targetHeight;
	$combinedRatio = $ratio / $targetRatio;

	// Cut X wise in source to avoid thumb image distortion
	if ($combinedRatio >= 1) {
		$thumbRatio = $height / $targetHeight;
		$startX = ($width - ($thumbRatio * $targetWidth)) / 2;
		$src_w = ($thumbRatio * $targetWidth);
		$startY = 0;
		$src_h = $height;
	}
	// Cut Y wise in source to avoid thumb image distortion
	else {
		$thumbRatio = $width / $targetWidth;
		$startY = ($height - ($thumbRatio * $targetHeight)) / 2;
		$src_h = ($thumbRatio * $targetHeight);
		$startX = 0;
		$src_w = $width;
	}
}`