Resize large images in App Engine

Question

I've got an app on Google App Engine that will accept image uploads from users. The problem that I envision is that users will upload these images directly from their cameras, and file sizes are often greater than 1MB, which is the limit for the image API (which would be used to resize the images).

What's the best way to accept the upload of say a 1.5MB image file, and resize it to under 1MB?

Answer 1

That's a conundrum. The "obvious" answer, using google.appengine.api.images.resize, won't work because it's too big. :) So you will have to use third-party software, either on the server (which will be tricky because of App Engine's limitations) or the cilent (e.g. a Java uploader).

Answer 2

Here are two (similar) ways to solve this:

1. If you want to keep everything controlled yourself, you can put a resize script on a server of yours, which takes the URL to the raw uploaded image (which can be up to 10MB due to HTTP response size limit, but you would have to store it as 1MB chunks in the datastore), downloads it from your application, resizes it, and then POSTs it back to your application. All this interaction would need some kind of authorization of course, so that it can't be abused. Alternatively, POST the image directly to your external server, but then you have to either send the other form data back to your application, or use a separate form for the image upload.
2. Use an external imaging service. I would recommend Picnik. See their API documentation. As you can see, it lets you make a form that posts the image directly to their servers, then the user can edit the image (and resize), then the image is posted back to your server. With this solution you have to upload the image in a separate form, since Picnik receives all your POST data.

I recommend point 2, because it doesn't require you to go around Google App Engine limitations and since your users are uploading images straight from the camera, they will probably want to do something with them anyways (such as crop.)