compare multiple images in ios in objective-C

Question

i am comparing images with each other here is the code for it.

for (int i=0; i<arrImageData.count; i++)
{
    for (int j=i+1; j<arrImageData.count; j++)
    {
        if ([arrImageData[i]isEqualToData:arrImageData[j]])
        {
            [arrImages addObject:arrImage[i]];
        }
    }
}

now problem is when number of images increase it takes too much time to calculate.is there any better solution for it?

I think That's not how [Images are compared](http://stackoverflow.com/questions/7749862/using-objective-c-is-there-any-way-to-compare-two-images-and-get-a-difference). — NSNoob, Dec 16 '15 at 12:30
assume there aree 1000 images...so it compare 1st image with other 999 images...after that 2nd image will compare with other 998 image..and so on...so it takes too much time to compute..give me better solution for this issue — Harshit, Dec 16 '15 at 12:31
yes.. i am comparing nsdata comparison works perfect but it takes time when there is high number of images — Harshit, Dec 16 '15 at 12:35
this comparison is works when data is exact copy of that data....if i want to do like "if 10% of image is same then it count as same image"..any solution for this?? — Harshit, Dec 16 '15 at 12:43
@Harshit But that's a completely different question. You'd first need to precisely define that partial equality. — meaning-matters, Dec 16 '15 at 12:50
i would ask diffrent question but then i think add into this... — Harshit, Dec 16 '15 at 12:59
Idk if hashes work this way (Comparison by percentage) but if you compare images pixel by pixel, you can see how much percent of images match each other. See accepted answer in my first comment — NSNoob, Dec 16 '15 at 14:03

score 1 · Answer 1 · edited May 23 '17 at 11:52

1

you should use hashes to compare big amount of data

1 you can compare UImage directrly: image1.hash == image2.hash

2 you can calculate your own hash for each image added to the array, it will be calculated once and used for every comparison

here is the hash algorithm https://en.wikipedia.org/wiki/MD5

PS it will works if image data is absolutely equal, it much more difficult to compare two different images with one "content" Image comparison - fast algorithm

edited May 23 '17 at 11:52

Community

1
1

answered Dec 16 '15 at 12:32

Igor

1,537
10
12

but i am comparing images one by one with each other thats why it takes too much time...anyother algorithm you suggest – Harshit Dec 16 '15 at 12:33
This should probably be a comment and _not_ an answer. – Ed Holloway-George Dec 16 '15 at 12:33

score 1 · Answer 2 · edited May 23 '17 at 12:31

1

I think you should use hashes for comparison. Refer this link: Generate hash from UIImage It will help you.

edited May 23 '17 at 12:31

Community

1
1

answered Dec 16 '15 at 12:33

Nilesh

438
5
15

score 0 · Answer 3 · answered Dec 16 '15 at 12:34

0

you can try something like this:

- (BOOL)image:(UIImage *)image1 isEqualTo:(UIImage *)image2{    
    return [UIImagePNGRepresentation(image1) isEqual:UIImagePNGRepresentation(image2)];
}

answered Dec 16 '15 at 12:34

Jiri Zachar

487
3
8

That's what he is doing. He wants to do it faster as he has a large set of images – NSNoob Dec 16 '15 at 12:36
this is the same as i m doing...i want faster method to compare lots of images... – Harshit Dec 16 '15 at 12:38

score 0 · Answer 4 · answered Dec 16 '15 at 13:55

You can use Fast Enumeration as Below

    for(UIImage *img in arrImageData)
    {
        for (UIImage *comImg in arrImageData) {
            if ([UIImageJPEGRepresentation(img, 0) isEqual:UIImageJPEGRepresentation(comImg, 0)]) {
                [arrImages addObject:img];
            }
        }
    }

Hope it helps you...!

compare multiple images in ios in objective-C

4 Answers4