Saving optimal JPEGs

ZSWFileTester.m

//
//  ZSWFileTester.m
//  Image Size Test
//
//  Created by Zachary West on 3/4/14.
//  Copyright (c) 2014 Zachary West. All rights reserved.
//

#import "ZSWFileTester.h"

@import MobileCoreServices;
@import ImageIO;

@implementation ZSWFileTester
+ (NSUInteger)fileSizeForImageIOVersionOfImage:(UIImage *)image {
    NSURL *destinationURL = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:@"test.jpg"]];
    
    CGImageDestinationRef destinationRef = CGImageDestinationCreateWithURL((__bridge CFURLRef)destinationURL,
                                                                           kUTTypeJPEG,
                                                                           /* number of images */ 1,
                                                                           /* reserved */ NULL);
    
    CGImageDestinationSetProperties(destinationRef,
                                    (__bridge CFDictionaryRef)@{
                                                                (__bridge NSString *)kCGImageDestinationLossyCompressionQuality: @(0.94)
                                                                });
    
    CGImageDestinationAddImage(destinationRef, image.CGImage, NULL);
    CGImageDestinationFinalize(destinationRef);
    CFRelease(destinationRef);

    NSNumber *fileSize;
    if ([destinationURL getResourceValue:&fileSize forKey:NSURLFileSizeKey error:NULL]) {
        return [fileSize unsignedIntegerValue];
    } else {
        NSAssert(NO, @"Booboo");
        return 0;
    }
}

+ (NSUInteger)fileSizeForUIImageVersionOfImage:(UIImage *)image {
    NSURL *destinationURL = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:@"test.jpg"]];
    [UIImageJPEGRepresentation(image, 0.94) writeToFile:destinationURL.path atomically:NO];
    
    NSNumber *fileSize;
    if ([destinationURL getResourceValue:&fileSize forKey:NSURLFileSizeKey error:NULL]) {
        return [fileSize unsignedIntegerValue];
    } else {
        NSAssert(NO, @"Booboo");
        return 0;
    }
}

+ (void)test {
    NSLog(@"Starting test... this will take a little bit.");
    
    NSURL *folderURL = [[[NSBundle mainBundle] bundleURL] URLByAppendingPathComponent:@"images"];
    
    NSDirectoryEnumerator *enumerator = [[NSFileManager defaultManager] enumeratorAtURL:folderURL
                                                             includingPropertiesForKeys:@[ ]
                                                                                options:0
                                                                           errorHandler:NULL];
    
    NSUInteger runningSizeCount = 0;
    CGFloat runningSizeDifference = 0;
    
    NSUInteger runningTimeCount = 0;
    NSTimeInterval runningTimeDifference = 0;
    
    for (NSURL *imageURL in enumerator) {
        NSTimeInterval imageIoTime, uiImageTime;
        NSUInteger imageIoSize, uiImageSize;
        
        @autoreleasepool {
            UIImage *image = [[UIImage alloc] initWithContentsOfFile:imageURL.path];
            
            NSDate *imageIoStart = [NSDate date];
            imageIoSize = [self fileSizeForImageIOVersionOfImage:image];
            imageIoTime = [[NSDate date] timeIntervalSinceDate:imageIoStart];
            
            NSDate *uiImageStart = [NSDate date];
            uiImageSize = [self fileSizeForUIImageVersionOfImage:image];
            uiImageTime = [[NSDate date] timeIntervalSinceDate:uiImageStart];
        }
        
#define UPDATE_RUNNING_AVG(result, count, new_value) \
    do { \
        result = ((result * count) + new_value)/(count+1); \
        count++; \
    } while (0)
        
        NSTimeInterval timeDifference = (imageIoTime - uiImageTime)/imageIoTime;
        UPDATE_RUNNING_AVG(runningTimeDifference, runningTimeCount, timeDifference);
        
        CGFloat sizeDifference = ((CGFloat)(uiImageSize - imageIoSize))/((CGFloat)uiImageSize);
        UPDATE_RUNNING_AVG(runningSizeDifference, runningSizeCount, sizeDifference);
        
        printf(".");
    }
    
    printf("\n");
    
    NSLog(@"Image IO creates files %.02f%% smaller than UIImage", runningSizeDifference*100);
    NSLog(@"Image IO takes %.02fx longer than UIImage", (1.0/runningTimeDifference));
}

@end