iOS将一张图片转换为交错式JPEG

#import 


- (NSData *)asProgressiveJPEGDataWithCompression:(CGFloat)Compression {
    
    NSString *path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0] stringByAppendingPathComponent:@"progressive.jpg"];
    NSURL *fileUrl = [NSURL fileURLWithPath:path isDirectory:YES];
    CFURLRef url = CFURLCreateWithString(kCFAllocatorDefault,  (__bridge CFStringRef)fileUrl.absoluteString, NULL);
    
    
    NSDictionary *jfifProperties = @{(__bridge NSString*)kCGImagePropertyJFIFIsProgressive:@(YES)};
    NSDictionary *properties = @{(__bridge NSString*)kCGImageDestinationLossyCompressionQuality:@(Compression),(__bridge NSString*)kCGImagePropertyJFIFDictionary:jfifProperties};
    
    
    CGImageDestinationRef destinationRef = CGImageDestinationCreateWithURL(url, kUTTypeJPEG, 1, (__bridge CFDictionaryRef)properties);
    CGImageDestinationAddImage(destinationRef, self.CGImage, (__bridge CFDictionaryRef)properties);
    CGImageDestinationFinalize(destinationRef);
    
    
    NSData *data = [NSData dataWithContentsOfFile:path];
    if (data) {
        return data;
    } else {
        return UIImageJPEGRepresentation(self, 1);
    }
}

注意：再转换的过程中，不要再次用 UIImagePNGRepresentation 或 UIImageJPEGRepresentation去获取NSData。这样会会破坏修改，应该直接将NSData返回，上传服务器。