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copied!<p>I used @jasamer's SwapTest UIImage category to force load my large UIImage (about 3000x2100 px) in a worker thread (with NSOperationQueue). This reduces the stutter time when setting the image into the UIImageView to an acceptable value (about 0.5 sec on iPad1).</p> <p>Here is SwapTest UIImage category... thanks again @jasamer :)</p> <p>UIImage+ImmediateLoading.h file</p> <pre><code>@interface UIImage (UIImage_ImmediateLoading) - (UIImage*)initImmediateLoadWithContentsOfFile:(NSString*)path; + (UIImage*)imageImmediateLoadWithContentsOfFile:(NSString*)path; @end </code></pre> <p>UIImage+ImmediateLoading.m file</p> <pre><code>#import "UIImage+ImmediateLoading.h" @implementation UIImage (UIImage_ImmediateLoading) + (UIImage*)imageImmediateLoadWithContentsOfFile:(NSString*)path { return [[[UIImage alloc] initImmediateLoadWithContentsOfFile: path] autorelease]; } - (UIImage*)initImmediateLoadWithContentsOfFile:(NSString*)path { UIImage *image = [[UIImage alloc] initWithContentsOfFile:path]; CGImageRef imageRef = [image CGImage]; CGRect rect = CGRectMake(0.f, 0.f, CGImageGetWidth(imageRef), CGImageGetHeight(imageRef)); CGContextRef bitmapContext = CGBitmapContextCreate(NULL, rect.size.width, rect.size.height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), CGImageGetColorSpace(imageRef), kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little ); //kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little are the bit flags required so that the main thread doesn't have any conversions to do. CGContextDrawImage(bitmapContext, rect, imageRef); CGImageRef decompressedImageRef = CGBitmapContextCreateImage(bitmapContext); UIImage* decompressedImage = [[UIImage alloc] initWithCGImage: decompressedImageRef]; CGImageRelease(decompressedImageRef); CGContextRelease(bitmapContext); [image release]; return decompressedImage; } @end </code></pre> <p>And this is how I create NSOpeationQueue and set the image on main thread...</p> <pre><code>// Loads low-res UIImage at a given index and start loading a hi-res one in background. // After finish loading, set the hi-res image into UIImageView. Remember, we need to // update UI "on main thread" otherwise its result will be unpredictable. -(void)loadPageAtIndex:(int)index { prevPage = index; //load low-res imageViewForZoom.image = [images objectAtIndex:index]; //load hi-res on another thread [operationQueue cancelAllOperations]; NSInvocationOperation *operation = [NSInvocationOperation alloc]; filePath = [imagesHD objectAtIndex:index]; operation = [operation initWithTarget:self selector:@selector(loadHiResImage:) object:[imagesHD objectAtIndex:index]]; [operationQueue addOperation:operation]; [operation release]; operation = nil; } // background thread -(void)loadHiResImage:(NSString*)file { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSLog(@"loading"); // This doesn't load the image. //UIImage *hiRes = [UIImage imageNamed:file]; // Loads UIImage. There is no UI updating so it should be thread-safe. UIImage *hiRes = [[UIImage alloc] initImmediateLoadWithContentsOfFile:[[NSBundle mainBundle] pathForResource:file ofType: nil]]; [imageViewForZoom performSelectorOnMainThread:@selector(setImage:) withObject:hiRes waitUntilDone:NO]; [hiRes release]; NSLog(@"loaded"); [pool release]; } </code></pre>

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