Resize Images in PHP (With 4 Lines Of Code!)

Welcome to a tutorial on how to resize images in PHP. So you have a project that deals with images, and want to resize them due to space restrictions… or maybe you just want to create thumbnails of the uploaded images.

That covers the basics, but how do we resize transparent images? Let us walk through with a few more examples – Read on!

 

 

TLDR – QUICK SLIDES

Fullscreen Mode – Click Here

 

TABLE OF CONTENTS

 

 

1) SIMPLE IMAGE RESIZE

<?php
// (A) READ THE ORIGINAL IMAGE
$original = imagecreatefrompng("PHP-resize-a.png"); // original 600 x 400 px

// (B) EMPTY CANVAS WITH REQUIRED DIMENSIONS
// IMAGECREATETRUECOLOR(WIDTH, HEIGHT)
$resized = imagecreatetruecolor(300, 200); // smaller by 50%

// (C) RESIZE THE IMAGE
// IMAGECOPYRESAMPLED(TARGET, SOURCE, TX, TY, SX, SY, TWIDTH, THEIGHT, SWIDTH, SHEIGHT)
imagecopyresampled($resized, $original, 0, 0, 0, 0, 300, 200, 600, 400);

// (D) SAVE/OUTPUT RESIZED IMAGE
imagepng($resized, "demoA.png");

// (E) OPTIONAL - CLEAN UP
imagedestroy($original);
imagedestroy($resized);

This is an actual working version of the introduction above, which should be very straightforward and easy. To resize an image – We only need to create an empty canvas, then copy and resize the source image over.

 

 

2) RESIZING TRANSPARENT IMAGES

<?php
// (A) READ THE ORIGINAL IMAGE
$original = imagecreatefrompng("PHP-resize-b.png"); // original 512 x 512 px

// (B) EMPTY CANVAS WITH REQUIRED DIMENSIONS
$resized = imagecreatetruecolor(256, 256); // smaller by 50%

// (C) PREFILL WITH TRANSPARENT LAYER
imagealphablending($resized, false);
imagesavealpha($resized, true);
imagefilledrectangle(
  $resized, 0, 0, 256, 256, 
  imagecolorallocatealpha($resized, 255, 255, 255, 127)
);

// (D) RESIZE THE IMAGE
imagecopyresampled($resized, $original, 0, 0, 0, 0, 256, 256, 512, 512);

// (E) SAVE/OUTPUT RESIZED IMAGE
imagepng($resized, "demoB.png");

// (F) OPTIONAL - CLEAN UP
imagedestroy($original);
imagedestroy($resized);

Yep, pretty much the same. We only added an extra section (C) – Set the $resized canvas to alpha (transparent), and fill it with a transparent layer before resizing.

 

 

3) RESIZE IMAGE FUNCTION

<?php
function resizer ($source, $destination, $size, $quality=null) {
// $source - Original image file
// $destination - Resized image file name
// $size - Single number for percentage resize
// Array of 2 numbers for fixed width + height
// $quality - Optional image quality. JPG & WEBP = 0 to 100, PNG = -1 to 9
 
  // (A) CHECKS
  $allowed = ["bmp", "gif", "jpg", "jpeg", "png", "webp"];
  $sExt = strtolower(pathinfo($source)["extension"]);
  $dExt = strtolower(pathinfo($destination)["extension"]);
  if (!in_array($sExt, $allowed)) { throw new Exception("$sExt - Invalid image file type"); }
  if (!in_array($dExt, $allowed)) { throw new Exception("$dExt - Invalid image file type"); }
  if (!file_exists($source)) { throw new Exception("Source image file not found"); }

  // (B) IMAGE DIMENSIONS
  $dimensions = getimagesize($source);
  $width = $dimensions[0];
  $height = $dimensions[1];
  if (is_array($size)) {
    $new_width = $size[0];
    $new_height = $size[1];
  } else {
    $new_width = ceil(($size/100) * $width);
    $new_height = ceil(($size/100) * $height);
  }

  // (C) RESIZE
  // (C1) RESPECTIVE PHP IMAGE FUNCTIONS
  $fnCreate = "imagecreatefrom" . ($sExt=="jpg" ? "jpeg" : $sExt);
  $fnOutput = "image" . ($dExt=="jpg" ? "jpeg" : $dExt);

  // (C2) IMAGE OBJECTS
  $original = $fnCreate($source);
  $resized = imagecreatetruecolor($new_width, $new_height); 

  // (C3) TRANSPARENT IMAGES ONLY
  if ($sExt=="png" || $sExt=="gif") {
    imagealphablending($resized, false);
    imagesavealpha($resized, true);
    imagefilledrectangle(
      $resized, 0, 0, $new_width, $new_height,
      imagecolorallocatealpha($resized, 255, 255, 255, 127)
    );
  }

  // (C4) COPY & RESIZE
  imagecopyresampled(
    $resized, $original, 0, 0, 0, 0, 
    $new_width, $new_height, $width, $height
  );

  // (D) OUTPUT & CLEAN UP
  if (is_numeric($quality)) {
    $fnOutput($resized, $destination, $quality);
  } else {
    $fnOutput($resized, $destination);
  }
  imagedestroy($original);
  imagedestroy($resized);
}

// (E) EXAMPLE USAGE
// (E1) PERCENTAGE RESIZE
resizer("PHP-resize-a.png", "demoC.jpg", 50);
resizer("PHP-resize-b.png", "demoD.png", 25);

// (E2) FIXED DIMENSION RESIZE + QUALITY
resizer("PHP-resize-a.png", "demoE.jpg", [150, 100], 60);
resizer("PHP-resize-b.png", "demoF.webp", [128, 128], 70);

Finally, this function is kind of a small convenience for you guys to use in your own projects – Basically, a “smart version” of the above examples that do checks and auto-dimension calculations. Not the best in the world, but should be good enough for a kickstart.

 

 

 

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EXAMPLE CODE DOWNLOAD

Click here for the source code on GitHub gist, just click on “download zip” or do a git clone. I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

 

 

 

SUMMARY OF FUNCTIONS

Function	Description	PHP Manual
imagecreatefromjpeg(FILE)	The whole family of imagecreatefromXXX() functions are used to create an image object from the specified file.	Click Here
imagecreatetruecolor(WIDTH, HEIGHT)	Create an empty canvas with a specified width and height.	Click Here
imagesavealpha(IMAGE, BOOL)	Set the image to retain the alpha channel (transparency).	Click Here
imagecopyresampled(DESTINATION, SOURCE, DX, DY, SX, SY)	Copy and resize.	Click Here
imagejpeg(IMAGE, FILE NAME)	The whole family of imageXXX() is used to save and output an image object.	Click Here
imagedestroy(IMAGE)	Destroy an image.	Click Here

 

LINKS & REFERENCES

• How do I resize pngs with transparency in PHP? – StackOverflow
• PHP Image Resize – PHPPot

 

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