detect brightness using ios camera

brightness.m

- (AVCaptureDevice *)frontCamera {
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    for (AVCaptureDevice *device in devices) {
        if ([device position] == AVCaptureDevicePositionFront) {
            return device;
        }
    }
    return nil;
}


- (void)setupAVCapture {
  
  //-- Setup Capture Session.
  _session = [[AVCaptureSession alloc] init];
  [_session beginConfiguration];
  
  //-- Set preset session size.
  [_session setSessionPreset:AVCaptureSessionPreset1920x1080];
  
  //-- Creata a video device and input from that Device.  Add the input to the capture session.
  AVCaptureDevice * videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
  if(videoDevice == nil)
  assert(0);
  
  //-- Add the device to the session.
  NSError *error;
  AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
  if(error)
  assert(0);
  
  [_session addInput:input];
  
  //-- Create the output for the capture session.
  AVCaptureVideoDataOutput * dataOutput = [[AVCaptureVideoDataOutput alloc] init];
  [dataOutput setAlwaysDiscardsLateVideoFrames:YES]; // Probably want to set this to NO when recording
  
  //-- Set to YUV420.
  [dataOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange]
                                                           forKey:(id)kCVPixelBufferPixelFormatTypeKey]]; // Necessary for manual preview
  
  // Set dispatch to be on the main thread so OpenGL can do things with the data
  [dataOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
  
  [_session addOutput:dataOutput];
  [_session commitConfiguration];
  
  [_session startRunning];
}

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
fromConnection:(AVCaptureConnection *)connection
{
  CFDictionaryRef metadataDict = CMCopyDictionaryOfAttachments(NULL,
                                                               sampleBuffer, kCMAttachmentMode_ShouldPropagate);
  NSDictionary *metadata = [[NSMutableDictionary alloc]
                            initWithDictionary:(__bridge NSDictionary*)metadataDict];
  CFRelease(metadataDict);
  NSDictionary *exifMetadata = [[metadata
                                 objectForKey:(NSString *)kCGImagePropertyExifDictionary] mutableCopy];
  self.autoBrightness = [[exifMetadata
                          objectForKey:(NSString *)kCGImagePropertyExifBrightnessValue] floatValue];
  
  float oldMin = -4.639957; // dark
  float oldMax = 4.639957; // light
  if (self.autoBrightness > oldMax) oldMax = self.autoBrightness; // adjust oldMax if brighter than expected oldMax
  
  self.lumaThreshold = ((self.autoBrightness - oldMin) * ((3.0 - 1.0) / (oldMax - oldMin))) + 1.0;
  
  NSLog(@"brightnessValue %f", self.autoBrightness);
  NSLog(@"lumaThreshold %f", self.lumaThreshold);
}