How to save a TIFF photo from AVFoundations captureStillImageAsynchronouslyFromConnection to a file with EXIF metadata on an iPhone (iOS)?

Question

With this question I only ask for the possibilities I have with Xcode and iOS without external libraries. I am already exploring the possibility of using libtiff in another question.

Problem

I have been sieving stack overflow for weeks and found working solutions for every one of my problems on its own. I have 4 things that need to work:

1. I need the RGBA data as it comes from the camera, no compression whatsoever
2. I need as much metadata as possible, especially EXIF
3. I need to save in TIFF format for compatibility with other software and losslessness
4. I need protection from casual viewing by saving in a file, not the photo library

I can have 2 and 4 by using JPEG. I can have 1, 3 and 4 with raw data (respectively NSData) made from the camera buffer. Can I have all 4 of my prerequisites with Xcode and iOS? I am about to give up and looking for your input as a last resort.

While still exploring this, I am also stuck on the other avenue I tried, libtiff. I am still trying, though...

Here is the list of great advice I have tried, my own code is just put together from stack overflow sources like these:

• How to write exif metadata to an image (not the camera roll, just a UIImage or JPEG) (makes me wish I could use JPEG format, it is so effortless when doing what Apple prefers)
• Raw image data from camera like “645 PRO” (this would be the point to use e.g. libtiff)
• Saving CGImageRef to a png file? (works with kUTTypeTIFF, too, but no metadata)

Solution

The complete sequence of actions from captureStillImageAsynchronouslyFromConnection:

[[self myAVCaptureStillImageOutput] captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
 {
     //get all the metadata in the image
     CFDictionaryRef metadata = CMCopyDictionaryOfAttachments(kCFAllocatorDefault, imageSampleBuffer, kCMAttachmentMode_ShouldPropagate);
     // get image reference
     CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(imageSampleBuffer);
     // >>>>>>>>>> lock buffer address
     CVPixelBufferLockBaseAddress(imageBuffer, 0);

     //Get information about the image
     uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
     size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
     size_t width = CVPixelBufferGetWidth(imageBuffer);
     size_t height = CVPixelBufferGetHeight(imageBuffer);

     // create suitable color space
     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

     //Create suitable context (suitable for camera output setting kCVPixelFormatType_32BGRA)
     CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);

     // <<<<<<<<<< unlock buffer address
     CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

     // release color space
     CGColorSpaceRelease(colorSpace);

     //Create a CGImageRef from the CVImageBufferRef
     CGImageRef newImage = CGBitmapContextCreateImage(newContext);

     // release context
     CGContextRelease(newContext);

     // create destination and write image with metadata
     CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:filePath isDirectory:NO];
     CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypeTIFF, 1, NULL);
     CGImageDestinationAddImage(destination, imageRef, metadata);

     // finalize and release destination
     CGImageDestinationFinalize(destination);
     CFRelease(destination);
 }

The still image output related camera settings were:

[[self myAVCaptureSession] setSessionPreset:AVCaptureSessionPresetPhoto];

and

NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA], (id)kCVPixelBufferPixelFormatTypeKey, nil];
[myAVCaptureStillImageOutput setOutputSettings:outputSettings];

I get a nice nominally uncompressed image in nominal TIFF format with all metadata. (It is mirrored on other systems, but now I can write the EXIF and other metadata, I can also fine-tune that, I am sure).

Thanks again to Wildaker for his help!

Answer 1

As you've already cracked 1, 3 and 4, it seems the only hurdle you're missing is saving the data and metadata together. Try this (assuming the unprocessed data is in a CMSampleBufferRef called myImageDataSampleBuffer and you've done the heavy lifting of putting the graphical data into a CGImageRef called myImage):

CFDictionaryRef metadata = CMCopyDictionaryOfAttachments(kCFAllocatorDefault,
  myImageDataSampleBuffer,
  kCMAttachmentMode_ShouldPropagate);
NSFileManager* fm = [[NSFileManager alloc] init];
NSURL* pathUrl = [fm URLForDirectory:saveDir
  inDomain:NSUserDomainMask
  appropriateForURL:nil
  create:YES
  error:nil];
NSURL* saveUrl = [pathUrl URLByAppendingPathComponent:@"myfilename.tif"];
CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)saveUrl,
  (CFStringRef)@"public.tiff", 1, NULL);
CGImageDestinationAddImage(destination, myImage, metadata);
CGImageDestinationFinalize(destination);
CFRelease(destination);