I suppose you just get a new image where the image is the log of the pixel value. It's used to enhance dark areas by expanding their range, while not clipping bright areas. Run the code below for a demo.
workspace; % Make sure the workspace panel is showing.
% Read in and display the original gray scale image.
grayImage = imread('Cameraman.tif');
grayImage = double(grayImage);
subplot(2,1,1);
imshow(grayImage, []);
axis on;
title('Original Image', 'FontSize', 15);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
% Take the log of it. Add 1 to avoid taking log of zero.
logImage = log(grayImage+1);
% Normalize to the range 0-1.
normalizedImage = mat2gray(logImage);
% Display it.
subplot(2,1,2);
imshow(normalizedImage, []);
axis on;
title('Log Image', 'FontSize', 15);
% If you want a uint8 version, then you can multiply by 255
% uint8Image = uint8(255 * normalizedImage);
msgbox('Note how the coat has more details');
