objective c - Compare RGB of two images in IOS -

in app need compare rgb of 2 images same or not. using 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 method returns same rgb value when setting image name.

@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];     // additional setup after loading view, typically 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 resources can 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(); }