有关PHP中图像缩略图性能的问题

Question

I have a function in PHP that resizes images into a thumbnail, my image upload script takes an uploaded image and runs this function to resize the image if it is wider then 700px it then also runs the function 2 more times to create 2 different sized thumbnail images, so there is a total of 3 images saved each time a user uploads an image. My resize/thumbnail function is called 2 times for the thumbnails and an occasional 3rd time if the file is to wide in dimensions.

Now this resizing function uses getimagesize( ) to get the dimensions, so my uplaod script calls this function, then the resizing function uses the getimagesize( ) function 2-3 more times to make other sized images.

I am thinking that I should just pass the dimesions onto the resize function since I get them in the uploading process?

My real question is, is getimagesize( ) a resource hungry functon, would it be best to use it at least as possible or is calling it a few times when 1 image is uploaded fine?

Answer 1

Just a tip/precausion, I asssume you're using GD functions. When creating more than one thumbnail, the usual bottleneck is wrongly implemented image resizing functions - each time reading the original image and then saving the resized one. A better way is to load the image once, and use the image resource to make all thumbnails with imagecopyresampled - don't only pass the dimentions of the image to the function - pass also the GD reference. Thay way your original file gets loaded only once.

Answer 2

For something that runs only on upload, it shouldn't bother so much. Uploading is not a action where the user expects super fast response. Premature optimization is the root of all evil .

That being said, getimagesize() is not particularly costly, but if you can call it just once do so. But I don't predict that much of a speed increase. The costly part of your script is the image resizing itself.

Answer 3

It's not particularly resource hungry - it has to open a file and read the image header.

Don't go out of your way to optimize it away - if it's easy, do it. Otherwise, wait and see where the real bottlenecks are in your application before optimizing.

Answer 4

The best thing to do is to profile your scripts.

Instead of theoretical answers which may not apply to a specific situation, you get a real answer and it is really instructive.

Also, with this habit, you will be able to :

• discover bottlenecks
• make the difference between a micro optimization and a major optimization.

I personally dev. on Windows and deploy on *nix.

On my dev dox, I use xdebug + WinCacheGrind to read the results.

I could not live without them. :)

http://elrems.wordpress.com/2008/02/12/profiling-php-with-xdebug-and-wincachegrind/

Answer 5

I don't think the uploading part should be where you resize the image. You should resize the image at a later time as a cron job. You can use a third party application like imagemagick or some other resizing application to resize images. That way you save time on the front end. You can run the resize job every 5 minutes or so.