How to save an image converted from RGB to greyscale?

I'm new to matlab and when I convert an RGB image to a greyscale intensity map, I can't get the output to save as a greyscale...it saves an an RGB. Is this because I am using imshow and then saving the figure? If so, can someone help me figure out how to work imwrite into this code? I'm using:

i = imread('sample.png');
i = im2double(i);
a = .299*i(:,:,1) + .587*i(:,:,2) + .114*i(:,:,3);
imshow(a);

Answer 1

[Walter Roberson]

imwrite(a, 'OutputFile.png')