Code snippets to show color detection problem using GPUImage

ColorDetect.m

#import "ColorDetectVC.h"

@interface ColorDetectVC ()
{
	GPUImageVideoCamera *videoCamera;
	GPUImageFilter *rotationFilter;
	GPUImageView *filteredVideoView;
	GPUImageRawData *positionRawData;
}
@end

@implementation ColorDetectVC
@synthesize centerView = _centerView;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
	
	[self configureVideoFiltering:AVCaptureDevicePositionBack];
	
}

- (void)viewDidUnload
{
	[self setCenterView:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

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

- (void)configureVideoFiltering:(AVCaptureDevicePosition)devicePosition
{
	CGRect mainScreenFrame = [[UIScreen mainScreen] applicationFrame];	
    videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:AVCaptureSessionPreset640x480 cameraPosition:devicePosition];
	
	filteredVideoView = [[GPUImageView alloc] initWithFrame:CGRectMake(0.0, 0.0, mainScreenFrame.size.width, mainScreenFrame.size.height)];
    [self.view addSubview:filteredVideoView];
	[self.view sendSubviewToBack:filteredVideoView];
	
	rotationFilter = [[GPUImageRotationFilter alloc] initWithRotation:kGPUImageRotateRight];
	
	CGSize videoPixelSize = CGSizeMake(480.0, 640.0);
	positionRawData = [[GPUImageRawData alloc] initWithImageSize:videoPixelSize];
    positionRawData.delegate = self;
	
	
	[videoCamera addTarget:rotationFilter];
	[rotationFilter addTarget:positionRawData];
	[rotationFilter addTarget:filteredVideoView];
	
	[videoCamera startCameraCapture];
}

#pragma mark - GPUImageRawDataProcessor

- (void)newImageFrameAvailableFromDataSource:(GPUImageRawData *)rawDataSource;
{
	if (rawDataSource == positionRawData)
    {
		CGRect mainScreenFrame = [[UIScreen mainScreen] applicationFrame];
		CGPoint centerPosition = CGPointMake(CGRectGetMidX(mainScreenFrame), CGRectGetMidY(mainScreenFrame));
		
		CGRect rect = _centerView.frame;
		rect.origin.x = centerPosition.x;
		rect.origin.y = centerPosition.y;
		[_centerView setFrame:rect];
		
		GPUByteColorVector colorVector = [rawDataSource colorAtLocation:centerPosition];
		float red = (float)colorVector.red;
		float green = (float)colorVector.green;
		float blue = (float)colorVector.blue;
		float alpha = (float)colorVector.alpha;
		
		NSLog(@"R:%f G:%f B:%f A:%f",red, green, blue, alpha);		
		UIColor *color = [UIColor colorWithRed:red/255.0 green:green/255.0 blue:blue/255.0 alpha:alpha/255.0];
		[_centerView setBackgroundColor:color];
	}
}