How to get shutter speed, aperture, and ISO values on iPhone - ios

Question

I have written code like this :
-(IBAction)startCapture
{
//session object
captureSession = [[AVCaptureSession alloc]init];
captureSession.sessionPreset = AVCaptureSessionPresetMedium;
AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:captureSession];
previewLayer.frame = CGRectMake(0, 10, 320, 200); ////self.view.frame; //
[self.view.layer addSublayer:previewLayer];
NSError *error = nil;
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
//input object
AVCaptureDeviceInput *inputDevice = [[AVCaptureDeviceInput alloc]initWithDevice:device error:&error];
[captureSession addInput:inputDevice];
stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil];
[stillImageOutput setOutputSettings:outputSettings];
[captureSession addOutput:stillImageOutput];
[captureSession startRunning];
}
-(IBAction) captureNow
{
AVCaptureConnection *videoConnection = nil;
for (AVCaptureConnection *connection in stillImageOutput.connections)
{
for (AVCaptureInputPort *port in [connection inputPorts])
{
if ([[port mediaType] isEqual:AVMediaTypeVideo] )
{
videoConnection = connection;
break;
}
}
if (videoConnection) { break; }
}
NSLog(#"about to request a capture from: %#", stillImageOutput);
[stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
{
CFDictionaryRef exifAttachments = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);
NSLog(#"exif Attachments:%#",exifAttachments);
if (exifAttachments)
{
NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
UIImage *image = [[UIImage alloc] initWithData:imageData];
self.vImage.image = image;
// Do something with the attachments.
}
else
NSLog(#"no attachments");
}];
}
to capture the images. But I want to know the shutter speed, ISO value and aperture while capturing. How can I find out these values? I tried the following:
[stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
{
CFDictionaryRef exifAttachments = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);
NSDictionary *exifDict = (NSDictionary *)exifAttachments;
NSLog(#"\n exif data = %#",exifDict);
CFNumberRef aperaturevalue = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifApertureValue, NULL);
NSNumber *num = (NSNumber *)aperaturevalue;
NSLog(#"\n AperatureValue : %#",num);
CFNumberRef shutter = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifShutterSpeedValue, NULL);
NSNumber *shunum = (NSNumber *)shutter;
NSLog(#"\n shuttervalue : %#",shunum);
CFArrayRef isoRef = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifISOSpeedRatings, NULL);
NSArray *iso = (NSArray *)isoRef;
NSLog(#"Iso value : %#",iso);
}
but it is giving output like this:
exif data = {
ApertureValue = "2.970853605202583";
ExposureMode = 0;
ExposureProgram = 2;
FNumber = "2.8";
Flash = 32;
MeteringMode = 1;
SceneType = 1;
SensingMethod = 2;
WhiteBalance = 0;
}
2011-06-23 14:35:14.955 CameraExample[1464:307]
AperatureValue : (null)
2011-06-23 14:35:14.981 CameraExample[1464:307]
shuttervalue : (null)
2011-06-23 14:35:14.999 CameraExample[1464:307] Iso value : (null)

Answer 1

Try to add this code in your block :
CFDictionaryRef exifDictRef = CMGetAttachment(imageSampleBuffer,kCGImagePropertyExifDictionary, NULL);
NSDictionary *exifDict = (NSDictionary *)exifDictRef;
for (id key in exifDict) {
NSLog(#"key = %#, value = %#",key,[exifDict objectForKey:key]);
}
You should find the values you are looking for in these keys :
kCGImagePropertyExifShutterSpeedValue (result is a NSNumber)
kCGImagePropertyExifApertureValue (result is a NSNumber)
kCGImagePropertyExifISOSpeedRatings (result is a NSArray)