CGImageSourceCreateThumbnailAtIndex crashes with 20MB Image - ios

Question

The following method for creating a thumbnail image crashes on an iPad when I test it with large images (ie > 10 MB). I've profiled it and Allocations doesn't report any large memory spikes - it stays consistently at 5 MB of living memory during the operation.
How can I create a thumbnail for an image so large? I've tried scaling it with Core Graphics but that is less memory efficient and doesn't work.
+(UIImage*) thumbnailImageAtPath:(NSString*) path withSize:(CGSize) size{
#autoreleasepool{
CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef)[NSURL fileURLWithPath:path], NULL);
if(!src){
return nil;
}
NSDictionary* options = #{
(id)kCGImageSourceShouldAllowFloat : (id)kCFBooleanTrue,
(id)kCGImageSourceCreateThumbnailWithTransform : (id)kCFBooleanFalse,
(id)kCGImageSourceCreateThumbnailFromImageIfAbsent : (id)kCFBooleanTrue,
(id)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithDouble:1024]
};
CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, (__bridge CFDictionaryRef)options);
// Doesn't reach here :(
UIImage* img = [[UIImage alloc] initWithCGImage:thumbnail];
NSLog(#"Size: %f, %f", size.width, size.height);
CGImageRelease(thumbnail);
CFRelease(src);
return img;
}
}
I've tried it on the main thread, worker threads, concurrently, non-concurrently, etc - it just doesn't seem to work on an actual device.
What's also strange is that it works brilliantly with a PDF of > 60 MB.

Answer 1

Try to remove option kCGImageSourceThumbnailMaxPixelSize... Ask me if not.
EDIT:
Try this code:
+ (UIImage*)scaleAndRotateImage:(UIImage *)image{
int kMaxResolution = 1024; // Or whatever 320
CGImageRef imgRef = image.CGImage;
CGFloat width;
CGFloat height;
width = CGImageGetWidth(imgRef);
height = CGImageGetHeight(imgRef);
CGAffineTransform transform = CGAffineTransformIdentity;
CGRect bounds = CGRectMake(0, 0, width, height);
if (width > kMaxResolution || height > kMaxResolution) {
CGFloat ratio = width/height;
if (ratio > 1) {
bounds.size.width = kMaxResolution;
bounds.size.height = bounds.size.width / ratio;
}
else {
bounds.size.height = kMaxResolution;
bounds.size.width = bounds.size.height * ratio;
}
}
CGFloat scaleRatio = bounds.size.width / width;
CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
CGFloat boundHeight;
UIImageOrientation orient = image.imageOrientation;
switch(orient) {
case UIImageOrientationUp: //EXIF = 1
transform = CGAffineTransformIdentity;
break;
case UIImageOrientationUpMirrored: //EXIF = 2
transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
transform = CGAffineTransformScale(transform, -1.0, 1.0);
break;
case UIImageOrientationDown: //EXIF = 3
transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
transform = CGAffineTransformRotate(transform, M_PI);
break;
case UIImageOrientationDownMirrored: //EXIF = 4
transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
transform = CGAffineTransformScale(transform, 1.0, -1.0);
break;
case UIImageOrientationLeftMirrored: //EXIF = 5
boundHeight = bounds.size.height;
bounds.size.height = bounds.size.width;
bounds.size.width = boundHeight;
transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
transform = CGAffineTransformScale(transform, -1.0, 1.0);
transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
break;
case UIImageOrientationLeft: //EXIF = 6
boundHeight = bounds.size.height;
bounds.size.height = bounds.size.width;
bounds.size.width = boundHeight;
transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
break;
case UIImageOrientationRightMirrored: //EXIF = 7
boundHeight = bounds.size.height;
bounds.size.height = bounds.size.width;
bounds.size.width = boundHeight;
transform = CGAffineTransformMakeScale(-1.0, 1.0);
transform = CGAffineTransformRotate(transform, M_PI / 2.0);
break;
case UIImageOrientationRight: //EXIF = 8
boundHeight = bounds.size.height;
bounds.size.height = bounds.size.width;
bounds.size.width = boundHeight;
transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
transform = CGAffineTransformRotate(transform, M_PI / 2.0);
break;
default:
[NSException raise:NSInternalInconsistencyException format:#"Invalid image orientation"];
}
UIGraphicsBeginImageContext(bounds.size);
CGContextRef context = UIGraphicsGetCurrentContext();
if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {
CGContextScaleCTM(context, -scaleRatio, scaleRatio);
CGContextTranslateCTM(context, -height, 0);
}
else {
CGContextScaleCTM(context, scaleRatio, -scaleRatio);
CGContextTranslateCTM(context, 0, -height);
}
CGContextConcatCTM(context, transform);
CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return imageCopy;}

Answer 2

I think I know what the issue was.
The png that I was using had quite a few alpha transparent pixels in it.
I'll have to run some definitive tests with different alpha/non-alpha images to confirm that was the problem, though. Will do that when I get a chance.

Answer 3

NSString *path = [[NSBundle mainBundle] pathForResource:#"LARGE_elevation" ofType:#"jpg"];
UIImage* image = [UIImage imageWithContentsOfFile:path];
image = [self scaleImage:image toSize:CGSizeMake(400, 200)];
- (UIImage *)scaleImage:(UIImage *)image
toSize:(CGSize)size
{
CGSize sz = image.size;
if(sz.width > size.width || sz.height > size.height) {
double ratio = MIN(sz.width / size.width, sz.height / size.height);
sz.width /= ratio;
sz.height /= ratio;
}
CGContextRef context;
UIGraphicsBeginImageContextWithOptions(size, NO, image.scale);
context = UIGraphicsGetCurrentContext();
CGContextSetGrayFillColor(context, 0.0, 1.0);
CGContextFillRect(context, CGRectMake(0, 0, size.width, size.height));
[image drawInRect:CGRectMake(0, 0, sz.width, sz.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
LARGE_elevation.jpg - 14.3 mb.