In this tutorial, we'll learn how to write a
function that will take an image, reduce it's dimensions with the GD
library, then (in this tutorial) store the image. You will need the GD2
library installed on your server in order to follow this guide.
Resizing and copying images
In
this tutorial, we'll learn how to write a function that will take an
image, reduce it's dimensions with the GD library, then (in this
tutorial) store the image. The function is easily editable to make the
requested image outputted, but that method doesn't have as many uses as
the storing method so we won't discuss it any further.
Before you continue, note that you will need the GD2 library installed on your server in order to follow this guide.
Without further space taking text, here is the function. We'll see how it works after you briefly skim it for its context.
function resize($filename, $max_width=200, $sendTo='/thumbnails/tmp.jpg') {
if ( !file_exists($file) )
return false;
$type = preg_replace('#.*?\.(.+)$#i', '\\1', $filename);
$path = $_SERVER['DOCUMENT_ROOT'] . $sendTo;
if ( !file_exists($path) ) {
$fp = @fopen($path, 'r+');
@chmod($path, 0777);
@fclose($fp);
}
if ( stristr($filename, '.jpg') ) {
$type = 'jpeg';
}
$func = 'imagecreatefrom' . $type;
// Content type
//header('Content-type: image/' . $type);
// Get new dimensions
list($width, $height) = getimagesize($filename);
# Calculate percent
$per = $width/$max_width;
$new_width = $max_width;
$new_height = $height / $per;
// Resample
$image_p = imagecreatetruecolor($new_width, $new_height);
$image = $func($filename);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
// Output
imagejpeg($image_p, $path, 100);
return true;
} // End function
Firstly, let's look at the argument list. The $filename argument is
self explanitory. This is the first argument and the only required one
in the list. This should be the path on the remote server to the image
you are wanting to edit.
The second argument is the max_width argument. If you're working with a
site like myspace, and the max width of pictures is typically 90pixels,
you could set the default value to this argument as 90. However, you
can still manually specify it each time you call the function.
Lastly is the path to store the new image. If you're not going to be
storing images and you're going to be outputting them to the browser,
you won't need to teter with this argument. However, the path that is
there will most likely not work on your remote server.
I've seen a few people request an argument change up as far as order
when I've posted this function other places. For me in my personal
uses, I'm constantly specifying the max width each time I call the
function and I'm not always specifying the storage path, so the current
setup works the best. But you can feel free to rearrange the optional
arguments all your wish.
Now, let's see the processes in the function itself. First, of course,
we check to see if the file being resized exists. If it doesn't, the
function returns with a false value. Note, no matter what, as long as
the file exists the function will return true. Assuming another error
occurs, in most cases PHP will arise a fatal error to stop the script
anyway.
Nextly, you should ensure that all the files being passed to the
resize() function are images. If they are not of image type, then PHP
will raise a fatal error when it calls "imagecreatefrom*" functions.
Then, we determine what type of image is being handled, and store the appropriate function name.
I have commented out a few lines of code that would cause the image to
outputted to the browser instead of stored. This is for flexibility to
those wanting to output the image.
Next, we calculate the new height for the image with the specified
width. Note that if an image is smaller than the specified dimensions,
it will be stretched. I have not included a very comprehensive
returning system for this function, but it is still quite effective and
fast.
Next, we store a blank image in the system memory using the
imagecreatetruecolor() function. Once we have the image's memory set
aside, we can copy the old image into the "dynamic clipboard" of the
$image variable.
Then we use the imagecopyresampled() function, which does just that. It
stores the contents of the old image with the new specified dimensions
into the memory space we created with imagecreatetruecolor().
Once we have the code for our new image, we're ready to output or store
it. In this case, we store it by specifying the second and optional
argument of the imagejpeg() function. The third parameter is just the
quality of the image, which I always set to 100 for best quality.
Now that we've looked at this function, you should note that it only
allows for jpeg output. This is easiy changed. You could call the
output function like this:
$outputFunc = 'image' . $type;
$outputFunc($image_p, $path);
I think you get the point. Well, that's the tutorial, hope you enjoyed
it! If you have questions about customizing it just ask away and I'll
answer them. This is just the source I use for a few sites of mine, so
I didn't want to completely modify it but I'm happy to answer questions
about it.
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