I am currently working on a PHP application which is ran from the command line to optimize a folder of Images.
The PHP application is more of a wrapper for other Image Optimizer’s and it simply iterates the directory and grabs all the images, it then runs the Image through the appropriate program to get the best result.
Below are the Programs that I will be using and what each will be used for…
imagemagick to determine file type and convert non-animated gif’s to png
gifsicle to optimize Animated Gif images
jpegtran to optimize jpg images
pngcrush to optimize png images
pngquant to optimize png images to png8 format
pngout to optimize png images to png8 format
My problem: With 1-10 images, everything runs smooth and fairly fast however, once I run on a larger folder with 10 or more images, it becomes really slow. I do not really see a good solution around this but one thing that would help is to avoid re-processing images that have already been Optimized. So if I have a folder with 100 images and I optimize that folder and then add 5 new images, re-run the optimizer. It then has to optimize 105 images, my goal is to have it only optimize the 5 newer images since the previous 100 would have already been optimized. This alone would greatly improve performance when new images are added to the image folder.
I realize the simple solution would be to simply copy or move the images to a new folder after processing them, my problem with that simple solution is that these images are used for the web and websites, so the images are generally hard-linked into a websites source code and changing the path to the images would complicate that and possibly break it sometimes.
Some ideas I have had are: Write some kind of text file database to the image folders that will list all the images that have already been processed, so when the application is ran, it will only run on images that are not in that file already. Another idea was to cheange the file name to have some kind of identification in the name to show it has been optimized, a third idea is to move each optimized file to a final destination folder once it is optimized. Idea 2 and 3 are not good though because they will break all image path links in the websites source code.
So please if you can think of a decent/good solution to this problem, please share?
Meta data
You could put a flag in the meta info of each image after it is optimized. First check for that flag and only proceed if it’s not there. You can use exif_read_data() to read the data. Writing it maybe like this.
The above is for JPGs. Metdata for PNGs is also possible take a look at this question, and this one.
I’m not sure about GIFs, but you could definitely convert them to PNGs and then add metadata… although I’m pretty sure they have their own meta info, since meta data extraction tools allow GIFs.
Database Support
Another solution would be to store information about the images in a MySQL database. This way, as you tweak your optimizations you could keep track of when and which optimization was tried on which image. You could pick which images to optimize according to any parameters of your choosing. You could build an admin panel for this. This method would allow easy experimentation.
You could also combine the above two methods.
Maximum File Size
Since this is for saving space, you could have the program only work on images that are larger than a certain file size. Ideally, after running the compressor once, all the images would be below this file size, and after that only newly added images that are too big would be touched. I don’t know how practical this is in terms of implementation, since it would require that the compressor gets any image below some arbitrary files size. You could make the maximum file size dependent on image size…..