Compute negative image processing pixel by pixel

Hi, so I just started using MATLAB, and I need to solve this exercise: "iven a 24bpp Image, write a MATLAB code to compute the "negative image". The solution must reach the result by processing pixel by pixel." I assume I have to use a for loop to process pixel by pixel; til now, I found this possible solution:

>> a = imread('nameOfTheImage.png'); 
>> d(:,:,3) = 255 - a(:,:,3);  
>> d(:,:,2) = 255 - a(:,:,2);  
>> d(:,:,1) = 255 - a(:,:,1); 
>> imshow([a,d])

but I think it's too simple. Can you help me with some indications? Thank you in advance!

Answer 1

[Rik]

Congratulation, you came up with a better solution than the one your instructor asked you. You can even make this one shorter:

a = imread('nameOfTheImage.png');
d=255-a;

But you needed to use a loop to access each pixel separately:

d=a;
for row=1:size(a,1)
    for col=1:size(a,2)
        d(row,col,:)=255-a(row,col,:);
    end
end

[Giorgio Gurian]

Thank you very much, this seems like the best solution, considering the request!

[Giorgio Gurian]

Also, can you give me a description of what every line of code does? Thanks!

[Rik]

You can open up the documentation with the doc command. There you can look at what the for and size functions do.

[Giorgio Gurian]

Thank you!