convert UIImage to NSData

Try one of the following, depending on your image format:

UIImageJPEGRepresentation

Returns the data for the specified image in JPEG format.

NSData * UIImageJPEGRepresentation (   UIImage *image,   CGFloat compressionQuality);

UIImagePNGRepresentation

Returns the data for the specified image in PNG format

NSData * UIImagePNGRepresentation (   UIImage *image);

Here the docs.

EDIT:

if you want to access the raw bytes that make up the UIImage, you could use this approach:

CGDataProviderRef provider = CGImageGetDataProvider(image.CGImage);NSData* data = (id)CFBridgingRelease(CGDataProviderCopyData(provider));const uint8_t* bytes = [data bytes];

This will give you the low-level representation of the image RGB pixels.(Omit the CFBridgingRelease bit if you are not using ARC).

NSData *imageData = UIImagePNGRepresentation(myImage.image);

If you have an image inside a UIImageView , e.g. "myImageView", you can do the following:

Convert your image using UIImageJPEGRepresentation() or UIImagePNGRepresentation() like this:

NSData *data = UIImagePNGRepresentation(myImageView.image);//orNSData *data = UIImageJPEGRepresentation(myImageView.image, 0.8);//The float param (0.8 in this example) is the compression quality //expressed as a value from 0.0 to 1.0, where 1.0 represents //the least compression (or best quality).

You can also put this code inside a GCD block and execute in another thread, showing an UIActivityIndicatorView during the process ...

//*code to show a loading view here*dispatch_queue_t myQueue = dispatch_queue_create("com.my.queue", DISPATCH_QUEUE_SERIAL);dispatch_async(myQueue, ^{     NSData *data = UIImagePNGRepresentation(myImageView.image);    //some code....    dispatch_async( dispatch_get_main_queue(), ^{        //*code to hide the loading view here*    });});