问题
A certain site I know recently upgraded their bandwith from 2,5 TB monthly to 3,5 TB.
Reason is they went over the 2,5 limit recently. They're complaining they don't know how to get down the bandwidth usage.
One thing I haven't seen them consider is the fact that JPEG and other images that are displayed on the site(and it is an image-heavy site) can contain metadata. Where the picture was taken and such.
Fact of the matter is, this information is of no importance whatsoever on that site. It's not gonna be used, ever. Yet it's still adding to the bandwidth, since it increases the filesize of every images from a few bytes to a few kilobytes.
On a site that uses up more then 2,5 TB per month, stripping the several thousands images of their metadata will help decrease the bandwidth usage at least by a few Gigabytes per month I think, if not more.
So is there a way to do this in PHP? And also, for the allready existing files, does anybody know a good automatic metadata remover? I know of JPEG & PNG Stripper, but that's not very good... Might be usefull for initial cleaning though...
回答1:
Check out Smush.it! It will strip all un-necs info from an image. They have an API you can use to crunch the images.
Note: By Design, it may change the filetype on you. This is on purpose. If another filetype can display the same image with the same quality, with less bytes it will give you a new file.
回答2:
It's trivial with GD:
$img = imagecreatefromjpeg("myimg.jpg");
imagejpeg($img, "newimg.jpg", $quality);
imagedestroy($img);
This won't transfer EXIF data. Don't know how much bandwidth it will actually save, though, but you could use the code above to increase the compression of the images. That would save a lot of bandwidth, although it possibly won't be very popular.
回答3:
I seriously doubt image metadata is the root of all evil here.
Some questions to take into consideration:
- How is the webserver configured?
- Does it issue http 304 responses properly?
- Isn't there some kind of hand-made caching/streaming of data through php scripting that prevents said data from being cached by the browser? (in which case, url rewriting and http redirections should be considered).
回答4:
I think you need to profile this. You might be right about it saving a few GB but thats relatively little on 2.5TB of bandwidth. You need real data about what is being served most and work on that. If you do find it is images that send your bandwidth usage so high you first should check your caching headers and 304 responses, you also might want to investigate using something like amazon S3 to serve your images. I have managed to reduce bandwidth costs a lot by doing this.
That said, if the EXIF data is really making that much of a difference then you can use the GD library to copy a jpeg image using the imagejpeg function. This won't copy EXIF data.
回答5:
Emil H's probably addresses the question the best.
But I wanted to add that this will almost certainly not save you as much as you may think. This type of metadata takes up very little space; I would think that
- Re-compressing the images to a smaller file size, and
- Cropping or resizing to reduce the resolution of the images
are both going to have a much greater effect. With point one alone you could probably drop bandwidth 50% and with both, you could drop bandwidth 80% - that is if you are willing to sacrifice some image size.
If not, you could always have the default view at a smaller size, with an 'enlarge' link. Most people just browsing will see the smaller image, and only those who want the largest size will click to enlarge it, so you'll still get almost all the bandwidth saving. This is what Flickr does, for example.
回答6:
Maybe some sort of hex data manipulation would help here. I'm facing the same problem and investigating on some sort of automated solution.
Just wondering if that can be done and if possible, I'll write a php class for this.
回答7:
Might be smart to do all the image manipulation on the client side (using a java applet such as facebook does) and then when the image is compressed, resized and fully stripped of unnecessary pixels and content, it can be uploaded at it's optimal size, saving you bandwidth and server side performance! (at the cost of initial development)
来源：https://stackoverflow.com/questions/676951/having-an-image-stripped-of-metadata-upon-upload-in-php