How to normalize disparity data in iOS?

There's a new blog post on raywenderlich.com called "Image Depth Maps Tutorial for iOS" contains sample app and details related to working with depth. The sample code shows how to normalize the depth data using a CVPixelBuffer extension:

extension CVPixelBuffer {

  func normalize() {

    let width = CVPixelBufferGetWidth(self)
    let height = CVPixelBufferGetHeight(self)

    CVPixelBufferLockBaseAddress(self, CVPixelBufferLockFlags(rawValue: 0))
    let floatBuffer = unsafeBitCast(CVPixelBufferGetBaseAddress(self), to: UnsafeMutablePointer<Float>.self)

    var minPixel: Float = 1.0
    var maxPixel: Float = 0.0

    for y in 0 ..< height {
      for x in 0 ..< width {
        let pixel = floatBuffer[y * width + x]
        minPixel = min(pixel, minPixel)
        maxPixel = max(pixel, maxPixel)
      }
    }

    let range = maxPixel - minPixel

    for y in 0 ..< height {
      for x in 0 ..< width {
        let pixel = floatBuffer[y * width + x]
        floatBuffer[y * width + x] = (pixel - minPixel) / range
      }
    }

    CVPixelBufferUnlockBaseAddress(self, CVPixelBufferLockFlags(rawValue: 0))
  }
}  

Something to keep in mind when working with depth data that they are lower resolution than the actual image so you need to scale up (more info in the blog and in the WWDC video)

Will's answer above is very good, but it can be improved as follows. I'm using it with depth data from a photo, it's possible that if the depth data doesn't follow 16-bits, as mentioned above, it won't work. Haven't found such a photo yet. I'm surprised there isn't a filter to handle this in Core Image.

extension CVPixelBuffer {

func normalize() {
    CVPixelBufferLockBaseAddress(self, CVPixelBufferLockFlags(rawValue: 0))
    
    let width = CVPixelBufferGetWidthOfPlane(self, 0)
    let height = CVPixelBufferGetHeightOfPlane(self, 0)
    let count = width * height

    let pixelBufferBase = unsafeBitCast(CVPixelBufferGetBaseAddressOfPlane(self, 0), to: UnsafeMutablePointer<Float>.self)
    let depthCopyBuffer = UnsafeMutableBufferPointer<Float>(start: pixelBufferBase, count: count)

    let maxValue = vDSP.maximum(depthCopyBuffer)
    let minValue = vDSP.minimum(depthCopyBuffer)
    let range = maxValue - minValue
    let negMinValue = -minValue

    let subtractVector = vDSP.add(negMinValue, depthCopyBuffer)
    let normalizedDisparity = vDSP.divide(subtractVector, range)
    pixelBufferBase.initialize(from: normalizedDisparity, count: count)

    CVPixelBufferUnlockBaseAddress(self, CVPixelBufferLockFlags(rawValue: 0))
}

}