how to use crop using coordinate?

hi. i want to crop the red square from this pic using coordinate. lets suppose coordinate of the top-left point of the red square is w/2 and h/2

where w and h are width and hight of the pic respectively. and width and hight of the red square are 20 pixel. this is my code but it dosent work. plz help me.

pic=imread('b.jpg');
[w, h, numberOfColorChannels] = size(pic);
I=imcrop(pic,[w*0.5 h*0.5 20 20]);
imshow(I)

[Spencer Chen]

Would be great if you describe what did not work.

[Rik]

Also, it is probably a good idea to round your coordinates to integers.

Answer 1

[Walter Roberson]

You need

[h, w, numberOfColorChannels] = size(pic);

not

[w, h, numberOfColorChannels] = size(pic);