Compare RGB of two images in IOS

Question

In my app I need to compare the RGB of two images are same or not. I am using this code...

-(CGFloat)compareImage:(UIImage *)imgPre capturedImage:(UIImage *)imgCaptured
{    

int colorDiff;
CFDataRef pixelData = CGDataProviderCopyData(CGImageGetDataProvider(imgPre.CGImage));
int myWidth = (int )CGImageGetWidth(imgPre.CGImage)/2;
int myHeight =(int )CGImageGetHeight(imgPre.CGImage)/2;
const UInt8 *pixels = CFDataGetBytePtr(pixelData);

int bytesPerPixel_ = 4;
int pixelStartIndex = (myWidth + myHeight) * bytesPerPixel_;
UInt8 alphaVal = pixels[pixelStartIndex];
UInt8 redVal = pixels[pixelStartIndex + 1];
UInt8 greenVal = pixels[pixelStartIndex + 2];
UInt8 blueVal = pixels[pixelStartIndex + 3];
UIColor *color = [UIColor colorWithRed:(redVal/255.0f) green:(greenVal/255.0f) blue:(blueVal/255.0f) alpha:(alphaVal/255.0f)];
NSLog(@"color of image=%@",color);
NSLog(@"color of R=%hhu/G=%hhu/B=%hhu",redVal,greenVal,blueVal);


CFDataRef pixelDataCaptured = CGDataProviderCopyData(CGImageGetDataProvider(imgCaptured.CGImage));
int myWidthCaptured = (int )CGImageGetWidth(imgCaptured.CGImage)/2;
int myHeightCaptured =(int )CGImageGetHeight(imgCaptured.CGImage)/2;
const UInt8 *pixelsCaptured = CFDataGetBytePtr(pixelDataCaptured);

int pixelStartIndexCaptured = (myWidthCaptured + myHeightCaptured) * bytesPerPixel_;
UInt8 alphaValCaptured = pixelsCaptured[pixelStartIndexCaptured];
UInt8 redValCaptured = pixelsCaptured[pixelStartIndexCaptured + 1];
UInt8 greenValCaptured = pixelsCaptured[pixelStartIndexCaptured + 2];
UInt8 blueValCaptured = pixelsCaptured[pixelStartIndexCaptured + 3];
UIColor *colorCaptured = [UIColor colorWithRed:(redValCaptured/255.0f) green:(greenValCaptured/255.0f) blue:(blueValCaptured/255.0f) alpha:(alphaValCaptured/255.0f)];
NSLog(@"color of captured image=%@",colorCaptured);
NSLog(@"color of captured image R=%hhu/G=%hhu/B=%hhu",redValCaptured,greenValCaptured,blueValCaptured);

colorDiff=sqrt((redVal-249)*(redVal-249)+(greenVal-greenValCaptured)*(greenVal-greenValCaptured)+(blueVal-blueValCaptured)*(blueVal-blueValCaptured));

return colorDiff;
} 

but this method returns same RGB value when I am setting image by name.

Answer 1

@interface ViewController ()<UIImagePickerControllerDelegate, UINavigationControllerDelegate>
{
    IBOutlet UIImageView *imgLeft;
    IBOutlet UIImageView *imgRight;

    IBOutlet UILabel *lblLeft;
    IBOutlet UILabel *lblRight;

    IBOutlet UILabel *lblResult;


    CGFloat redLeft,GreenLeft,BlueLeft;
    CGFloat redRight,GreenRight,BlueRight;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    UITapGestureRecognizer * tapRecognizerLeft = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageTappedLeft:)];
    [imgLeft addGestureRecognizer:tapRecognizerLeft];
    imgLeft.userInteractionEnabled = YES;

    UITapGestureRecognizer * tapRecognizerRight = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageTappedRight:)];
    [imgRight addGestureRecognizer:tapRecognizerRight];
    imgRight.userInteractionEnabled = YES;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

-(IBAction)calculateDistance:(id)sender
{
    CGFloat derivedRedDiff=redLeft-redRight;
    if (derivedRedDiff<0) {
        derivedRedDiff*=-1;
    }
    CGFloat derivedGreenDiff=GreenLeft-GreenRight;
    if (derivedGreenDiff<0) {
        derivedGreenDiff*=-1;
    }
    CGFloat derivedBlueDiff=BlueLeft-BlueRight;
    if (derivedBlueDiff<0) {
        derivedBlueDiff*=-1;
    }

    CGFloat distance=sqrtf(derivedRedDiff*derivedRedDiff+derivedGreenDiff*derivedGreenDiff+derivedBlueDiff*derivedBlueDiff);
    NSLog(@"Distance = %f",distance);
    lblResult.text=[NSString stringWithFormat:@"Distance = %f",distance];
}



-(void)imageTappedLeft:(UITapGestureRecognizer *)recognizer
{
    CGPoint point = [recognizer locationInView:imgLeft];

    UIGraphicsBeginImageContext(imgLeft.bounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [imgLeft.layer renderInContext:context];

    int bpr =(int) CGBitmapContextGetBytesPerRow(context);
    unsigned char * data = CGBitmapContextGetData(context);
    if (data != NULL)
    {
        int offset = bpr*round(point.y) + 4*round(point.x);
        int blue = data[offset+0];
        int green = data[offset+1];
        int red = data[offset+2];
        int alpha =  data[offset+3];

        CGFloat derivedAlpha=alpha/255.0f;

        NSLog(@"%d %d %d %d %f", alpha, red, green, blue,derivedAlpha);

        redLeft=red;
        GreenLeft=green;
        BlueLeft=blue;

        lblLeft.text=[NSString stringWithFormat:@"%d %d %d %f", red, green, blue,derivedAlpha];
    }

    UIGraphicsEndImageContext();
}

-(void)imageTappedRight:(UITapGestureRecognizer *)recognizer
{
    CGPoint point = [recognizer locationInView:imgRight];

    UIGraphicsBeginImageContext(imgRight.bounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [imgRight.layer renderInContext:context];

    int bpr =(int) CGBitmapContextGetBytesPerRow(context);
    unsigned char * data = CGBitmapContextGetData(context);
    if (data != NULL)
    {
        int offset = bpr*round(point.y) + 4*round(point.x);
        int blue = data[offset+0];
        int green = data[offset+1];
        int red = data[offset+2];
        int alpha =  data[offset+3];

        CGFloat derivedAlpha=alpha/255.0f;

        NSLog(@"%d %d %d %d %f", alpha, red, green, blue,derivedAlpha);

        redRight=red;
        GreenRight=green;
        BlueRight=blue;

        lblRight.text=[NSString stringWithFormat:@"%d %d %d %f", red, green, blue,derivedAlpha];
    }

    UIGraphicsEndImageContext();
}