Question

I am using the iPhone/iPad camera to get a video stream and doing recognition on the stream, but with lighting changes it has a negative impact on the robustness. I have tested different settings in different light and can get it to work, but trying to get the settings to adjust at run time is what I need.

I can calculate a simple brightness check on each frame, but the camera adjusts and throws my results off. I can watch for sharp changes and run checks then, but gradual changes would throw my results off as well.

Ideally I’d be like to access the camera/EXIF data for the stream and see what it is registering the unfiltered brightness as, is there a way to do this?

(I am working for devices iOS 5 and above)

Thank you

Answer 1

Available in iOS 4.0 and above. It’s possible to get EXIF information from CMSampleBufferRef.

//Import ImageIO & include framework in your project. 
#import <ImageIO/CGImageProperties.h>

In your sample buffer delegate toll-free bridging will get a NSDictionary of results from CoreMedia’s CMGetAttachment.

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    NSDictionary* dict = (NSDictionary*)CMGetAttachment(sampleBuffer, kCGImagePropertyExifDictionary, NULL);