Question

I’m using jQuery’s imgAreaSelect plugin in order to crop an image and save the thumbnail to use in cases where, for example, the ratio changes. Unfortunelly the results are far from what I would expect, and I can’t get it right. The image gets resized as a whole instead of being cropped.

Here’s the test example :

<?php

/***
*
* $_GET returned values
*
* x1 = 0
* x2 = 400
* y1 = 66
* y2 = 258
* w = 400
* h = 192
* folder = widethumb
* filename = IMG_4591.jpg
* scale = 48
*
* Original image properties
*
* width = 600px
* height = 900px
*
***/

define('DOCROOT', realpath(dirname(__FILE__)).DIRECTORY_SEPARATOR);

extract($_GET);

$fn = $filename;
$filename = DOCROOT.$filename;

list($width, $height) = getimagesize($filename);

$src = imagecreatefromjpeg($filename);
$dst = imagecreatetruecolor($w, $h);
imagecopyresampled($dst, $src, 0, 0, (int) $x1, (int) $y1, (int) $w, (int) $h, $width, $height);

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

What am I mising here?

Cheers!

Answer 1

From PHP Documentation:

bool imagecopyresampled ( resource $dst_image , resource $src_image , int $dst_x , int $dst_y , int $src_x , int $src_y , int $dst_w , int $dst_h , int $src_w , int $src_h )

imagecopyresampled() copies a rectangular portion of one image to another image, smoothly interpolating pixel values so that, in particular, reducing the size of an image still retains a great deal of clarity.

In other words, imagecopyresampled() will take an rectangular area from src_image of width src_w and height src_h at position (src_x,src_y) and place it in a rectangular area of dst_image of width dst_w and height dst_h at position (dst_x,dst_y).

So to get the result you are looking for, you need to avoid scaling. for that use:

imagecopy($dst, $src, 0, 0, $x1, $y1, $w, $h);

// this can also be done but is less efficient (over 10 times slower)
imagecopyresampled($dst, $src, 0, 0, (int) $x1, (int) $y1, $w, $h, $w, $h);

Here we are are taking the same sized rectangle from source as we are putting it into destination image.
I have just tested it and it works just fine.

Update:
I have just tried again on my test server and it is working fine. I’m using following code:

$filename = "test.jpg";

extract($_GET);

$src = imagecreatefromjpeg($filename);
$dst = imagecreatetruecolor($w, $h);
imagecopy($dst, $src, 0, 0, $x1, $y1, $w, $h);

// this is over 10 times slower, as we are only cropping we should use imagecopy
//imagecopyresampled($dst, $src, 0, 0, $x1, $y1, $w, $h, $w, $h);

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

And I’m calling it like this:

http://localserver/test/gd_crop.php?x1=906&y1=267&w=501&h=355

Performance Update
As we are not resizing we can simply use imagecopy. Performance of 3 functions as i have measured is given below.

imagecopyresampled    69ms
imagecopyresized      5.5ms
imagecopy             4.5ms

So there is an order of 10 speed difference between resampled and the two other functions.

I have finally come up with following line in place of imagecopyresampled function, try it, I have also updated the above code listing:

imagecopy($dst, $src, 0, 0, $x1, $y1, $w, $h);