Avfoundation troubles

[Teknoman117]

I develop for iPhone os 4.0 and I need the raw images from the camera on the phone for my app. I successfully have video input but the image is over exposed. My test device is an iPhone 3G and the continuous auto exposure in on but not helping.

This is the .h file

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
#import <CoreGraphics/CoreGraphics.h>
#import <CoreVideo/CoreVideo.h>
#import <CoreMedia/CoreMedia.h>

@interface VideoTestViewController : UIViewController <AVCaptureVideoDataOutputSampleBufferDelegate> {
	AVCaptureSession *_captureSession;
	UIImageView *_imageView;
	CALayer *_customLayer;
	AVCaptureVideoPreviewLayer *_prevLayer;
}

@property (nonatomic, retain) AVCaptureSession *captureSession;
@property (nonatomic, retain) UIImageView *imageView;
@property (nonatomic, retain) CALayer *customLayer;
@property (nonatomic, retain) AVCaptureVideoPreviewLayer *prevLayer;

- (void)initCapture;

@end

This is the .m file

#import "VideoTestViewController.h"

@implementation VideoTestViewController

@synthesize captureSession = _captureSession;
@synthesize imageView = _imageView;
@synthesize customLayer = _customLayer;
@synthesize prevLayer = _prevLayer;

- (void)viewDidLoad {
    [super viewDidLoad];
	self.imageView = nil;
	self.prevLayer = nil;
	self.customLayer = nil;
	[self initCapture];
}

- (void)initCapture {
	AVCaptureDevice* captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
	//[captureDevice unlockForConfiguration];
	AVCaptureDeviceInput *captureInput = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:nil];
	AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init];
	captureOutput.alwaysDiscardsLateVideoFrames = YES;
	[captureOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
	NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
	NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA];
	NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key];
	[captureOutput setVideoSettings:videoSettings];
	self.captureSession = [[AVCaptureSession alloc] init];
	[self.captureSession addInput:captureInput];
	[self.captureSession addOutput:captureOutput];
	[self.captureSession startRunning];
	[captureDevice lockForConfiguration:nil];
	if([captureDevice isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance]) {
		NSLog(@"Using decent white balance");
		[captureDevice setWhiteBalanceMode:AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance];
	}
	if([captureDevice isExposureModeSupported:AVCaptureExposureModeContinuousAutoExposure]) {
		NSLog(@"Using decent exposure mode");
		[captureDevice setExposureMode:AVCaptureExposureModeContinuousAutoExposure];
	}
	if([captureDevice isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus]) {
		NSLog(@"USing decent focusing mode");
		[captureDevice setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
	}
	self.imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
	[self.view addSubview:self.imageView];
}

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer,0);
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef newImage = CGBitmapContextCreateImage(newContext);
	CVPixelBufferUnlockBaseAddress(imageBuffer,0);
    CGContextRelease(newContext);
    CGColorSpaceRelease(colorSpace);
	UIImage *image= [UIImage imageWithCGImage:newImage scale:1.0 orientation:UIImageOrientationRight];
	self.imageView.image = image;
	CGImageRelease(newImage);
} 


- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (void)viewDidUnload {
	self.imageView = nil;
	self.customLayer = nil;
	self.prevLayer = nil;
}

- (void)dealloc {
	[self.captureSession release];
    [super dealloc];
}

[Teknoman117]

Sorry for the false alarm. The video is not being over exposed. The avcapturedeviceinput is returning an image with 128 for the alpha value. It can be fixed using this simple code snippet after it reads the settings in the delegate handler.

	for(int c=0;c<width*height;c++) {
		baseAddress[4*c+3] = 255;
	}