i need to read matrix from a png file

i'm new to matlab and i need help regarding my assignment

to start with i was given 3 png files

• image1.png,
• image2.png,
• image3.png

each image is consist of a 30x30 matrix each element in the matrix has a value from 0-50

1. i have to use the imread function to 'read' the matrix

• A = imread(image1.png);
• B = imread(image2.png);
• C = imread(image3.png);

question; is there a way that i can read all the 3 matrix without writing the imread program three times as shown above?? using a loop perhaps???

2.next is i have to set a limit to each of the element any number from 0-50

example: limit = input(enter a limit: ')

question: if the limit entered is greater than 50, how do you tell matlab to ask the user to input another value until it is within the range acceptable?

3. Say i;ve set the limit to 30

question how do i write a program that will count the number of element in the each of matrix which exceeds the value of the limit?

the result should look like this;

• A has 135 elements which exceeded the limit
• B has......................................
• C has......................................

thanks

Answer 1

[Matt Tearle]

answer (1) Yes, a for loop will do the job. You need a string in each pass through the loop to represent the file name. You can achieve this a couple of ways. One is to build the string by concatenating the components. You will need num2str. The other is to get a listing of the filenames, then index into that list. You will need to use ls or dir.

answer (2) A while loop will do this for you.

answer (3) Take a look at the nnz function. You will like it.

Answer 2

[Paulo Silva]

for ni=1:3
I{ni}= imread(sprintf('image%s.png',num2str(ni)));
end

limit=-1;
while (limit<0) | (limit>50)
disp('')  
limit=input('enter the limit [0-50]:')
disp('')
end

fprintf('A has %d elements which exceeded the limit\n',sum(sum(sum(I{1}>limit))))

[Matt Tearle]

Paulo, maybe Alexis is using the word "assignment" to mean something fairly general, but I think this may be a homework problem...

[Paulo Silva]

Hi Matt, that's homework for sure and usually I don't do homeworks but sometimes I'm looking for a challenge, the code I post isn't that good on purpose so the OP can improve it and understand how it works, with your detailed explanation I'm sure the OP will do it.

[Sean de Wolski]

I hear you on that Paulo. It means we're due for a Hump Day Challenge.

Answer 3

[avenge.]

Hey guys,

just to let you know, this "homework" looks a lot like a 25% first year Engineering Computing assignment I was given just a few days ago.

What do you think are the odds that this question is actually the same one, given that the timing is almost perfect??? ;)

[Matt Tearle]

Well, all the components are pretty standard tasks that are asked on probably hundreds of coursework assignments all the time. But if the combination and all the details are the same, it seems likely to be the same assignment. I've seen very similar questions here before -- could be the same person with multiple usernames, could be different people from the same class, could be random coincidence.