iOS. Load image downsampled to specified max pixel size.

ImageUtils.m

+ (UIImage *)thumbnailImageFromURL:(NSURL*)imageUrl downsampledToMaxPixelSize:(NSNumber *)maxPixelSize {
	NSDictionary *opts = @{
		(id)kCGImageSourceThumbnailMaxPixelSize: maxPixelSize,
		(id)kCGImageSourceCreateThumbnailWithTransform: (id)kCFBooleanTrue,
		(id)kCGImageSourceCreateThumbnailFromImageIfAbsent: (id)kCFBooleanTrue
	};
	CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef)imageUrl, NULL);
	CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, (__bridge CFDictionaryRef)opts);
	
	UIImage *img = [UIImage imageWithCGImage:thumbnail];
	
	CGImageRelease(thumbnail);
	CFRelease(src);
	
	return img;
}