CGContextDrawImage camera app crashes

Question

Hello All,
My first post on this forum. I am trying to obtain an image using the AVCaptureSession. I followed this tutorial http://www.benjaminloulier.com/posts/2-ios4-and-direct-access-to-the-camera. I am creating uiimage from image ref and then obtaining pixels from that uiimage. But the app crashes after sometime (less than 30s). I tried analyzing using Leaks and that too crashes. Using logs I found the app crashes just before the line  CGContextDrawImage(context, rect, image1.CGImage); Do you guys have any suggestions on what I might be doing wrong. I also see Memory Allocation errors a few seconds before the app crashes. Please help.
Please find the code below:
// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBufferCMSampleBufferRef) sampleBuffer
lock = @"YES";
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
// Lock the base address of the pixel buffer
CVPixelBufferLockBaseAddress(imageBuffer, 0);
// Get the number of bytes per row for the pixel buffer
void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
// Get the number of bytes per row for the pixel buffer
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
// Get the pixel buffer width and height
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
// Create a device-dependent RGB color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
size_t bufferSize = CVPixelBufferGetDataSize(imageBuffer);
// Create a Quartz direct-access data provider that uses data we supply.
NSData *data = [NSData dataWithBytes:baseAddress length:bufferSize];
CGDataProviderRef dataProvider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
CGImageRef quartzImage = CGImageCreate(width, height, 8, 32, bytesPerRow,
              colorSpace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little,
              dataProvider, NULL, true, kCGRenderingIntentDefault);
CGDataProviderRelease(dataProvider);
// Unlock the pixel buffer
CGColorSpaceRelease(colorSpace);
// Create an image object from the Quartz image
UIImage *image = [UIImage imageWithCGImage:quartzImage];
// Release the Quartz image
CGImageRelease(quartzImage);
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
baseAddress = nil;
[data  release];
lock = @"NO";
return(image);
-(void)calculate
@try {
        UIImage *image1 = [self stillImage];   //Capture an image from the camera.
        //Extract the pixels from the camera image.
        CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
        size_t bytesPerRow = image1.size.width*4;
        unsigned char* bitmapData = (unsigned char*)malloc(bytesPerRow*image1.size.height);
        CGContextRef context = CGBitmapContextCreate(bitmapData, image1.size.width, image1.size.height, 8, bytesPerRow,colourSpace,kCGImageAlphaPremultipliedFirst|kCGBitmapByteOrder32Big);
        CGColorSpaceRelease(colourSpace);
        CGContextDrawImage(context, rect, image1.CGImage);
        unsigned char* pixels = (unsigned char*)CGBitmapContextGetData(context);
        totalLuminance = 0.0;
        for(int p=0; p<image1.size.width*image1.size.height*4; p+=4)
            totalLuminance += pixels[p]*0.3 + pixels[p+1]*0.59 + pixels[p+2]*0.11;
        totalLuminance /= (image1.size.height * image1.size.width);                  
        pixels = nil;
        bitmapData = nil;
        [image1 release];
    CGContextRelease(context);
        //image1 = nil;
        //totalLuminance = [n floatValue];                   //Calculate the total luminance.
        float f = [del.camcont.slider value];
        float total = totalLuminance * f;
        NSString *ns = [NSString stringWithFormat:@"Lux : %0.2f", total];
        NSLog(@"slider = %f",f);
        NSLog(@"totlaluminance = %f",totalLuminance);
        NSLog(@"%@",ns);
        //NSString *ns = [NSString initWithFormat:@"Lux : %0.2f", total];
        [del.camcont.lux setText:ns];//Display the total luminance.
        self.stillImage = nil;
        //[self.stillImage release];
         ns = nil;
        //n = nil;
        //del = nil;
    @catch (NSException *exception) {
        NSLog(@"main: Caught %@: %@", [exception name], [exception reason]);

Answer 1

The error happens in the Calculate method which uses the Image retrieved from the AVCaptureSession ImageBuffer to do some calculations. Calculate method is called every second directly from the function which gets the still image.
A few seconds later I get Memory Allocation Error at line:
for(int p=0; p<image1.size.width*image1.size.height*4; p+=4)
   totalLuminance += pixels[p]*0.3 + pixels[p+1]*0.59 + pixels[p+2]*0.11;
And then after a few iterations crashes at the line
CGContextDrawImage(context, rect, image1.CGImage);
Can someone please guide me on how I can make sure I am releasing the memory allocated to objects properly.
Thanks