Resizing images on Windows Phone 7 on thread pool thread?

Question

I'm writing a Windows Phone 7 app that deals with a lot of images - These images can range from a few hundred pixels up to 1080P (Potentially higher in future).

Images are very resource intensive so I've gone down the path of caching + resizing images on the phone before displaying them.

This means on first time setup after a user has entered the IP address of the image store I can ask them to wait a few minutes while it's all retrieved/resized/cached. From then on they can have nice and snappy performance.

At the moment my cache manager tracks Images by a dictionary of Uri's and file locations. I have a Queue that processes up to 5 images at a time (Async web requests, resizing is semi done on thread pool thread).

The problem I have is that the WritableBitmap class in Silverlight is a UI element, meaning I have to transition to the UI thread via the Dispatcher to do the actual resizing which is stupid and slows the whole thing down - It also means my Cache Manager is effectively single threaded.

So it goes Cache Manager (Thread Pool) -> Async Web request (Thread Pool) -> Callback (Thread Pool) -> Resizing (UI Thread) -> Marking cache job as complete (Thread Pool).

I've been looking for a 3rd party library that will A) Compile and run on Windows Phone 7 and B) Be able to resize images of various formats by manipulating a stream or byte array and not be dependent on the UI thread.

Any one had any experience with this?

Cheers,

Tyler

Answer 1

In order to reduce the download size and in order to remove the burden of processing from the phone CPU, then I'd push this work out to a web service.

For example, you could host a service like the open source WebImageResizer code somewhere online http://webimageresizer.codeplex.com/ - e.g. on a free AppHarbor server.

Or you could use a commercial (freemium) service like:

• http://webresizer.com/app/
• http://www.appspotimage.com/

Either of these would enable you to rapidly process the images on a server with a superfast connection and to juse deliver smaller images to the phone with its limited data connection.