iPhone - Get a pointer to the data behind CGDataProvider?

Question

I'm trying to take a CGImage and copy its data into a buffer for later processing. The code below is what I have so far, but there's one thing I don't like about it - it's copying the image data twice. Once for CGDataProviderCopyData() and once for the :getBytes:length call on imgData. I haven't been able to find a way to copy the image data directly into my buffer and cut out the CGDataProviderCopyData() step, but there has to be a way...any pointers? (...pun ftw)

NSData *imgData = (NSData *)(CGDataProviderCopyData(CGImageGetDataProvider(myCGImageRef)));

CGImageRelease(myCGImageRef);

// i've got a previously-defined pointer to an available buffer called "mybuff"
[imgData getBytes:mybuff length:[imgData length]];

Answer 1

Unless you see a performance problem when you use Instruments to measure it, I don't think that copying it twice is a huge problem. You could always store the CFDataRef imgData directly instead of the mybuff.

Edit
I'm talking about this kind of code:
In your class interface add an array:

NSMutableArray *images;

In your init: method: create the array:

images = [[NSMutableArray alloc] init];

and have a dealloc;

-(void)dealloc{
    [images release];
}

and in your code that saves each image:

CGDataRef imageDataRef = CGDataProviderCopyData(CGImageGetDataProvider(myCGImageRef)));
[images addObject: (NSData*)imageDataRef];
CGRelease(imageDataRef);

Answer 2

See this answer: http://stackoverflow.com/questions/2744639/cocoa-does-cgdataprovidercopydata-actually-copy-the-bytes-or-just-the-point

Looks like direct access to the buffer behind a CGDataProvider is restricted to private APIs.