The memory size occupied by an image

I did not understand why when I save a 2D matrix (200 * 200) in an image (imwrite), the memory size occupied by this image is less than the memory occupied by the image created by a matrix (1 * 25000). the number of elements in the first case is greater than in the second.

do you have any explanation?

Thank you

Answer 1

[Steven Lord]

Compression, perhaps.

Let me generate a random matrix. What's the most compact way you can think of to write a command to regenerate it? [I'm not going to give you the command I used to generate it.]

A =

     1     8     8    -6    -6
     3     7    -5    -7     8
     0    10   -10    -9    -6
     9   -10     5     5    -9
     5    -8     1    10    -6

Here's a second matrix, same size. Can you write a shorter command to generate B than you could to generate A?

B =

     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0
     0     0     0     0     0

Even if I gave you the full command to create A, it would still be longer than the command I used to generate B.

[K. Taieb]

Thank you!

In my case, the matrixes are of type uint16 like B in your example.

I will show you an example:

I have a matrix A with 40000 elements and B with 25000 elements.

A=200*ones(200,200);
B=200*ones(25000,1);
imwrite(A,['image' num2str(1) '.jp2']);
imwrite(B,['image' num2str(2) '.jp2']);

The size of memory :

for B: image 1 = 240 byte.

for A: image 2 = 4,11 kilobyte.

I thought that the memory size occupied by the image 1 is more important because the nomber of elements of A is more then in B.