Saving masked UIImage to disk

Question

Hi there, I'm trying to save a multiple masked image to disk.

The code below explains How I do it. The maskImagewithStroke masks 2 times a picture : first time to provide an irregular stroke to a texture then I'm remasking it with a bigger mask to get a stroke from it. It's the bast way I found to get an irregular stroke around my texture. Now, for the sake of the iPhone and its performance, I'd like to generate all masked textures and save them to disk. I'll use thos files in another app to load premasked textures. the masking process is perfect on screen but when saving file i'm have a black image with the irregular stroke BUT without texture in it ... How may I change that ?

I'm calling the method masImageWihStrokandSaveToFile to launch the maskin + saving process..

-(void)masImageWihStrokandSaveToFile:(UIImage *)image withMask:(UIImage *)maskImage imageIndex:(NSInteger)i{
    //mask image with stroke
    //[self maskImageWithStroke:image withMask:maskImage];
    //save masked image to disk
    // Create paths to output images
    NSString  *pngPath = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"Documents/Test_%d.png",i]];
    NSString  *jpgPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Test.jpg"];

    // Write a UIImage to JPEG with minimum compression (best quality)
    // The value 'image' must be a UIImage object
    // The value '1.0' represents image compression quality as value from 0.0 to 1.0
    [UIImageJPEGRepresentation([self maskImageWithStroke:image withMask:maskImage], 1.0) writeToFile:jpgPath atomically:YES];

    // Write image to PNG
    [UIImagePNGRepresentation([self maskImageWithStroke:image withMask:maskImage]) writeToFile:pngPath atomically:YES];

    // Let's check to see if files were successfully written...

    // Create file manager
    NSError *error;
    NSFileManager *fileMgr = [NSFileManager defaultManager];

    // Point to Document directory
    NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];

    // Write out the contents of home directory to console
    NSLog(@"Documents directory: %@", [fileMgr contentsOfDirectoryAtPath:documentsDirectory error:&error]);
}

- (UIImage *) maskImageWithStroke:(UIImage *)image withMask:(UIImage *)maskImage{
    UIImage* maskedImage = [self maskImage:image withMask:maskImage];

    //****** Add a Stroke - Begin *******//
    //grow the actual mask
    UIImage* biggerMaskImage = [maskImage scaleToSize:CGSizeMake(310,310)];
    //now add a stroke to the image.

    //UIImage *bottomImage = [UIImage imageNamed:@"bottom.png"];
    //UIImage *image = [UIImage imageNamed:@"top.png"];

    CGSize newSize = CGSizeMake(310, 310);
    UIGraphicsBeginImageContext( newSize );

    // Use existing opacity as is
    //[biggerMaskImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
    //[biggerMaskImage drawInRect:CGRectMake(0,0,410,410)];
    [maskImage drawInRect:CGRectMake(0,0,310,310)];
    // Apply supplied opacity
    //[retImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.8];
    [maskedImage drawInRect:CGRectMake(0,0,300,300) blendMode:kCGBlendModeNormal alpha:1];


    UIImage *maskedStrokedImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    //****** Add a Stroke - End *******//

    //****** Remask - Begin ******//

    maskedStrokedImage = [self maskImage:maskedStrokedImage withMask:biggerMaskImage];

    //****** Remask - End ******//

    return maskedStrokedImage;
}

/*************Mask Images ***************/

CGImageRef CopyImageAndAddAlphaChannel(CGImageRef sourceImage) {
    CGImageRef retVal = NULL;

    size_t width = CGImageGetWidth(sourceImage);
    size_t height = CGImageGetHeight(sourceImage);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef offscreenContext = CGBitmapContextCreate(NULL, width, height, 
                                                          8, 0, colorSpace, kCGImageAlphaPremultipliedFirst);

    if (offscreenContext != NULL) {
        CGContextDrawImage(offscreenContext, CGRectMake(0, 0, width, height), sourceImage);

        retVal = CGBitmapContextCreateImage(offscreenContext);
        CGContextRelease(offscreenContext);
    }

    CGColorSpaceRelease(colorSpace);

    return retVal;
}

// masker method
- (UIImage*)maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
    CGImageRef maskRef = maskImage.CGImage;
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);

    CGImageRef sourceImage = [image CGImage];
    CGImageRef imageWithAlpha = sourceImage;
    //add alpha channel for images that don't have one (ie GIF, JPEG, etc...)
    //this however has a computational cost
    if (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNone) { 
        imageWithAlpha = CopyImageAndAddAlphaChannel(sourceImage);
    }

    CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);

    CGImageRelease(mask);

    //release imageWithAlpha if it was created by CopyImageAndAddAlphaChannel
    if (sourceImage != imageWithAlpha) {
        CGImageRelease(imageWithAlpha);
    }

    UIImage* retImage = [UIImage imageWithCGImage:masked];
    //UIImage* retImage = [UIImage imageWithCGImage:maskedTransparent];
    CGImageRelease(masked);

    return retImage;
}