Are all grayscale images of the size 256*256. Please clarify

I am using a .png image for processing. I converted it to grayscale and the value shown for the image is 289x318 uint8.. When I used [r c d]= size(I), I got r= 289, c=318 and d=1. Does it mean that my image has been grayscaled or not? And what does size 256*256 mean? Does it signify the values inside the matrix?

Answer 1

[Thorsten]

The size of your image is 289 x 318, as returned by the size command. Why do you think that the size is 256*256? A grayscale image can be of any size, only some of them are of size 256 x 256. The range of values are from 0 to 255, for a uint8 type image, so each pixel can take one from 256 different values. But that's the value of a pixel and has nothing to do with the size.

[N/A]

Thank you Thorsten. In the image processing I am working on they require a grayscale matrix of size 256*256. Is there a way to change the image size into 256*256?

[Thorsten]

You can crop the image

I = I(1:256, 1:256);

You can also resize the image using imresize, if it is square, or use a combination of resizing and cropping:

 [r, c] = size(I);
 I = imresize(I, 256/min(r,c));
 I = I(1:256, 1:256);

[N/A]

Il try that out. Thank you very much.