imagecopyresampled sometimes creating blank images - php

Question

I am resizing images using:
//load file and dimensions
$obj_original_image = imagecreatefromjpeg($str_file_path);
list($int_width, $int_height, $image_type) = getimagesize($str_file_path);
//compress file
$int_thumbnail_width = 320;
$int_ratio = $int_thumbnail_width / $int_width;
$int_new_width = $int_thumbnail_width;
$int_new_height = $int_height * $int_ratio;
$obj_image = imagecreatetruecolor($int_new_width, $int_new_height);
imagecopyresampled($obj_image, $obj_original_image, 0, 0, 0, 0, $int_new_width, $int_new_height, $int_width, $int_height);
imagejpeg($obj_image, $GLOBALS['serverpath'] . '/images/uploaded/video-thumbs/'.$arr_data['thumbnail_folder'].'/' . $arr_data['id']. '.jpg', $int_compression = 85);
And this is generally working perfectly. However occasionally, it is producing a blank, white image. I have read this note at http://php.net/manual/en/function.imagecopyresampled.php:
There is a problem due to palette image limitations (255+1 colors). Resampling or filtering an image commonly needs more colors than 255, a kind of approximation is used to calculate the new resampled pixel and its color. With a palette image we try to allocate a new color, if that failed, we choose the closest (in theory) computed color. This is not always the closest visual color. That may produce a weird result, like blank (or visually blank) images. To skip this problem, please use a truecolor image as a destination image, such as one created by imagecreatetruecolor().
However, I am already using imagecreatetruecolor. I am always scaling the same sized images so it can't be a width/height issue. It is only happening sometimes, most times the image scaling is working fine. Any ideas as to how to fix this?

Answer 1

There's no reason to be using getimagesize() when you've already opened the image with imagecreatefromjpeg(). You can use the imagesx() and imagesy() to get the width/height. getimagesize is seperate from GD and will re-open the image, re-parse it, etc...
Also note that GD is pretty stupid and forces you to determine what image type you've got and call the appropriate createfrom function. imagecreatefromjpeg() will fail if you try to open anything OTHER than a .jpg image.
$obj_original_image = imagecreatefromjpeg($str_file_path);
if ($obj_original_image === FALSE) {
die("Unable to load $str_file_path. Not a jpg?");
}
etc... etc...
$status = imagecopyresampled($obj_image, $obj_original_image, 0, 0, 0, 0, $int_new_width, $int_new_height, $int_width, $int_height);
if ($status === FALSE) {
die("imagecopyresampled failed!");
}
As well, add some debugging to your height/width calculations - output the values you're generating. Maybe one or more of them is coming out as 0, so you end up resampling to a non-existent size.

Answer 2

You mentioned that the size of the image being processed is always the same, but is the resolution always the same? If you have a particularly high resolution image you're working with, you may be running out of memory for certain operations which will produce a blank white image, in my experience. If this is the case, you could try to fix it by increasing the amount of memory allocated to PHP in php.ini under the memory_limit parameter. As far as I know, that value applies to image manipulations.