Why do I get "Array indices must be positive integers or logical values." error?

Hello!! When I try to run the following code, I get this error "Array indices must be positive integers or logical values." and I don't understand why.

img=imread('Barbara.bmp'); colormap(gray(256));
image(img); axis off; truesize;
S=2;img2=img(1:S:end,1:S:end);
figure; colormap(gray(256));
image(img2); axis off; truesize;

The error comes from line 1. Do I have to install anything to make it work?

[Stephen23]

@Ali Marie Avila Wragg: please show us the complete error message. This means all of the red text.

[Ali Marie Avila Wragg]

Array indices must be positive integers or logical values.

Error in Apartado3 (line 1)

img=imread('Barbara.bmp'); colormap(gray(256));

Answer 1

[Walter Roberson]

You probably have a variable named colormap that is interfering with using the function colormap

[Mohammad Mobayenjarihani]

thank you!