Save depth images from TrueDepth camera

Question

I am trying to save depth images from the iPhoneX TrueDepth camera. Using the AVCamPhotoFilter sample code, I am able to view the depth, converted to grayscale format, on the screen of the phone in real-time. I cannot figure out how to save the sequence of depth images in the raw (16 bits or more) format.

I have depthData which is an instance of AVDepthData. One of its members is depthDataMap which is an instance of CVPixelBuffer and image format type kCVPixelFormatType_DisparityFloat16. Is there a way to save it to the phone to transfer for offline manipulation?

Answer 1

There's no standard video format for "raw" depth/disparity maps, which might have something to do with AVCapture not really offering a way to record it.

You have a couple of options worth investigating here:

1. Convert depth maps to grayscale textures (which you can do using the code in the AVCamPhotoFilter sample code), then pass those textures to AVAssetWriter to produce a grayscale video. Depending on the video format and grayscale conversion method you choose, other software you write for reading the video might be able to recover depth/disparity info with sufficient precision for your purposes from the grayscale frames.

2. Anytime you have a CVPixelBuffer, you can get at the data yourself and do whatever you want with it. Use CVPixelBufferLockBaseAddress (with the readOnly flag) to make sure the content won't change while you read it, then copy data from the pointer CVPixelBufferGetBaseAddress provides to wherever you want. (Use other pixel buffer functions to see how many bytes to copy, and unlock the buffer when you're done.)

   Watch out, though: if you spend too much time copying from buffers, or otherwise retain them, they won't get deallocated as new buffers come in from the capture system, and your capture session will hang. (All told, it's unclear without testing whether a device has the memory & I/O bandwidth for much recording this way.)