Conversion of RGB Image into Intensity Image

Here I am adding a simple code which performs sharpening of an image:

% Clears command prompt and closes all windows
clear all;
close all;

% Read in image and display

im = imread('coin.png');
figure;
imshow(im);

% Create special unsharp mask filter
mask = fspecial('unsharp');
out = imfilter(im, mask);

% Display sharpened result
figure;
imshow(out);

My problem is that: I am operating the process on an 8 bit intensity image(which is named as 'coin' here), but after I perform the operation and save it, it automatically gets converted into an RGB image (8 bit). So, is there any procedure to get the resultant image ('out') as the same 8 bit intensity image? Please help me in this regard.

Thanks!

[Image Analyst]

How are you saving it? for example are you calling imwrite() and telling it to save as a BMP or JPG?

[Amith Kamath]

could you please clarify what you mean by 8 bit RGB image? When I follow your code example, I see that 'out' is a 246x300 uint8, which is the same type as 'im'. Typically, RGB images have 3 layers, each of which are typically 8 bit wide.