iOS faster way to update UIView with series of JPEGs ie MJPEG. (Instruments shows 50% CPU) - ios

Question

I'm receiving a series of JPEGs over the network from a camera (MJPEG). I display the images as I receive them in a UIView. What I'm seeing is that my App is spending 50% of CPU (device and simulator tested) in what appears to me to be the UIView update.
Is there is a less CPU intensive way to do this screen update? Should I process the JPEG in some way before handing it over to UIView?
Receive method:
UIImage *image = [UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(),^{
[cameraView updateVideoImage:image];
});
Update method:
- (void) updateVideoImage:(UIImage*)image {
myUIView.image = image;
...
update: added better screen capture
update2: Is OpenGL going to provide a quicker surface to render to for JPEG? It's not clear to me from Instruments where the time is being spent, render or decode. I'm going to put together a test case as suggested and work from there.

Answer 1

iOS is optimized for PNG images. While JPEG greatly reduces the size of images for transmission, it is a much more complex format, so it does not surprise me that this rendering is taking a lot of time. People have said there is jpeg hardware assist on the device, but I do not know for sure and even if its there it maybe tuned for certain image types.
So - some suggestions. Devise a test where you take one jpeg you have now, and render it to a context, and baseline this time. Take the same image and open it in Preview, then save it with a slightly different quality value to another file, and try that (Preview will strip out unnecessary "junk" from the image, or even convert it first to a png then back to a jpeg. The idea here is to use an image output from Preview, which is going to be as clean an image as you are going to get. Is the image any better?
You can also try using libjpegturbo, and see if it can render your images faster. You can see that library in action in a github project, PhotoScrollerNetwork. You may find that project of use as it decodes the jpegs (using that library) in real time as they are received, and then supports zoomable viewing using CATiledLayers.