Question

I wish to compress the image before storing it as an NSData object.

Below is the code, that helps me take NSData object of an Image.

NSURL *referenceURL = [info objectForKey:UIImagePickerControllerReferenceURL];
        ALAssetsLibrary *library1 = [[ALAssetsLibrary alloc] init];
        [library1 assetForURL:referenceURL resultBlock:^(ALAsset *asset)
         {

             int byteArraySize = asset.defaultRepresentation.size;

             NSMutableData* rawData = [[NSMutableData alloc]initWithCapacity:byteArraySize];
             void* bufferPointer = [rawData mutableBytes];

             NSError* error=nil;
             [asset.defaultRepresentation getBytes:bufferPointer fromOffset:0 length:byteArraySize error:&error];
             if (error) {
                 NSLog(@"%@",error);
             }
             rawData = [NSMutableData dataWithBytes:bufferPointer length:byteArraySize];
}

Any Help will be appreciated.

Answer 1

UIImagePickerController does return a compressed image, but you can control the format and compression as well with this built in UIKit function and a related function for PNGs:

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

You might need to create an NSURL if referenceURL returns a string.

NSImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL: referenceURL]];
NSData *compressedImage = UIImageJPEGRepresentation(image, .1); //.1 is low quality