I have two images taken by projecting laser light onto a agar plate. We have taken images at starting point and after an interval of 20 minutes, where we cultured bacteria on it. Then we applied imsubtract(a,b), (b,a) both giving different answers ?

a=imread('im5.jpg');
b=imread('im7.jpg');
c=imsubtract(a,b):
imshow(c)
d=imsubtract(b,a);
imshow(d)

after that in the output side we got greenish and red color image. Here we used a red color laser light. My question is, is that greenish color represents bacterial colony or anything else. Why the output is changing after interchanging these a,b to b,a in 'imsubtract' function? Following are the images: mat1 - for imsubtract(a,b) and mat2 - for imsubtract(b,a).

Answer 1

[KALYAN ACHARJYA]

Yes, how you expect that both gives the same results?

A-B !=B-A (!=>Not Equal)

Note: Subtraction and division functions are Not Commutative.

In your case

imsubtract(a,b)=a-b 

and

imsubtract(b,a)=b-a 

Both are not same.

[GUDIVADA ROKESH KUMAR]

Thank you for your response. But I attached the output images, from that could you tell me what resembles these green colored area in it.

[KALYAN ACHARJYA]

I have answered, what you have asked in the question. I hope you also agreed that both subtraction results are not same.

Though I will try- Define the following

• mat1.jpg
• mat2.jpg
• im5.jpg
• im7.jpg