How to compare images using opencv in iOS (iPhone)

Question

I want to compare 2 images taken by iPhone camera in my project. I am using OpenCV for doing that. Is there any other better way to do that? If i got the % similarity, It will be great.

I am using OpenCV following code for image comparison:

-(void)opencvImageCompare{ 
 NSMutableArray *valuesArray=[[NSMutableArray alloc]init];
 IplImage *img = [self CreateIplImageFromUIImage:imageView.image];
// always check camera image
 if(img == 0) {
   printf("Cannot load camera img");

}

IplImage  *res; 
CvPoint   minloc, maxloc;
double    minval, maxval;
double values;

UIImage *imageTocompare = [UIImage imageNamed:@"MyImageName"];
IplImage *imageTocompareIpl = [self CreateIplImageFromUIImage:imageTocompare];
// always check server image 
if(imageTocompareIpl == 0) {
    printf("Cannot load serverIplImageArray image");
}
if(img->width-imageTocompareIpl->width<=0 && img->height-imageTocompareIpl->height<=0){
    int balWidth=imageTocompareIpl->width-img->width;
    int balHeight=imageTocompareIpl->height-img->height;
    img->width=img->width+balWidth+100;
    img->height=img->height+balHeight+100;
}



CvSize size = cvSize(
                     img->width  - imageTocompareIpl->width  + 1,
                     img->height - imageTocompareIpl->height + 1
                     );

res = cvCreateImage(size, IPL_DEPTH_32F, 1);

// CV_TM_SQDIFF CV_TM_SQDIFF_NORMED
// CV_TM_CCORR  CV_TM_CCORR_NORMED
// CV_TM_CCOEFF CV_TM_CCOEFF_NORMED

cvMatchTemplate(img, imageTocompareIpl, res,CV_TM_CCOEFF);
cvMinMaxLoc(res, &minval, &maxval, &minloc, &maxloc, 0);
printf("\n value %f", maxval-minval);
values=maxval-minval;
NSString *valString=[NSString stringWithFormat:@"%f",values];
[valuesArray addObject:valString];
weedObject.values=[valString doubleValue];
printf("\n------------------------------");

cvReleaseImage(&imageTocompareIpl);

cvReleaseImage(&res);
}
cvReleaseImage(&img);

}

For the same image I am getting non zero result (14956...) and if I pass different image its crash.

Answer 1

Try this code - it compare images pixel by pixel

-(void)removeindicator :(UIImage *)image
{
    for (int i =0; i < [imageArray count]; i++)
    {
        CGFloat width =100.0f;
        CGFloat height=100.0f;

        CGSize newSize1 = CGSizeMake(width, height); //whaterver size
        UIGraphicsBeginImageContext(newSize1);
        [[UIImage imageNamed:[imageArray objectAtIndex:i]] drawInRect:CGRectMake(0, 0, newSize1.width, newSize1.height)];
         UIImage *newImage1 = UIGraphicsGetImageFromCurrentImageContext();
         UIGraphicsEndImageContext();

        UIImageView *imageview_camera=(UIImageView *)[self.view viewWithTag:-3];

        CGSize newSize2 = CGSizeMake(width, height); //whaterver size
        UIGraphicsBeginImageContext(newSize2);
        [[imageview_camera image] drawInRect:CGRectMake(0, 0, newSize2.width, newSize2.height)];
         UIImage *newImage2 = UIGraphicsGetImageFromCurrentImageContext();
         UIGraphicsEndImageContext();


       float numDifferences = 0.0f;
       float totalCompares = width * height;

       NSArray *img1RGB=[[NSArray alloc]init];
       NSArray *img2RGB=[[NSArray alloc]init];

      for (int yCoord = 0; yCoord < height; yCoord += 1)
      {
          for (int xCoord = 0; xCoord < width; xCoord += 1)
          {
              img1RGB = [self getRGBAsFromImage:newImage1 atX:xCoord andY:yCoord];
              img2RGB = [self getRGBAsFromImage:newImage2 atX:xCoord andY:yCoord];


              if (([[img1RGB objectAtIndex:0]floatValue] - [[img2RGB objectAtIndex:0]floatValue]) == 0 || ([[img1RGB objectAtIndex:1]floatValue] - [[img2RGB objectAtIndex:1]floatValue]) == 0 || ([[img1RGB objectAtIndex:2]floatValue] - [[img2RGB objectAtIndex:2]floatValue]) == 0)
              {
                 //one or more pixel components differs by 10% or more
                 numDifferences++;
              }
           }
       }

    // It will show result in percentage at last
      CGFloat percentage_similar=((numDifferences*100)/totalCompares);
      NSString *str=NULL;

      if (percentage_similar>=10.0f)
      {
          str=[[NSString alloc]initWithString:[NSString stringWithFormat:@"%i%@ Identical", (int)((numDifferences*100)/totalCompares),@"%"]];

              UIAlertView *alertview=[[UIAlertView alloc]initWithTitle:@"i-App" message:[NSString stringWithFormat:@"%@ Images are same",str] delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];
              [alertview show];

            break;
       }
      else
      {
          str=[[NSString alloc]initWithString:[NSString stringWithFormat:@"Result: %i%@ Identical",(int)((numDifferences*100)/totalCompares),@"%"]];

          UIAlertView *alertview=[[UIAlertView alloc]initWithTitle:@"i-App" message:[NSString stringWithFormat:@"%@ Images are not same",str] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
          [alertview show];
      }
  }

}

-(NSArray*)getRGBAsFromImage:(UIImage*)image atX:(int)xx andY:(int)yy
{
    //NSArray *result = [[NSArray alloc]init];
    // First get the image into your data buffer
    CGImageRef imageRef = [image CGImage];
    NSUInteger width = CGImageGetWidth(imageRef);
    NSUInteger height = CGImageGetHeight(imageRef);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));
    NSUInteger bytesPerPixel = 4;
    NSUInteger bytesPerRow = bytesPerPixel * width;
    NSUInteger bitsPerComponent = 8;
    CGContextRef context = CGBitmapContextCreate(rawData, width, height,
                                              bitsPerComponent, bytesPerRow, colorSpace,
                                             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
   CGColorSpaceRelease(colorSpace);

   CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
   CGContextRelease(context);

   // Now your rawData contains the image data in the RGBA8888 pixel format.
   int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;
   //    for (int ii = 0 ; ii < count ; ++ii)
  //    {
   CGFloat red   = (rawData[byteIndex]     * 1.0) / 255.0;
   CGFloat green = (rawData[byteIndex + 1] * 1.0) / 255.0;
   CGFloat blue  = (rawData[byteIndex + 2] * 1.0) / 255.0;
   //CGFloat alpha = (rawData[byteIndex + 3] * 1.0) / 255.0;
   byteIndex += 4;

   // UIColor *acolor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];

   //}
   free(rawData);

   NSArray *result = [NSArray arrayWithObjects:
                   [NSNumber numberWithFloat:red],
                   [NSNumber numberWithFloat:green],
                   [NSNumber numberWithFloat:blue],nil];

   return result;
}

Answer 2

try this code, It compares images bit by bit, ie 100%

UIImage *img1 = // Some photo;
UIImage *img2 = // Some photo;

NSData *imgdata1 = UIImagePNGRepresentation(img1);

NSData *imgdata2 = UIImagePNGRepresentation(img2);

if ([imgdata1 isEqualToData:imgdata2]) 
{
NSLog(@"Same Image");
}