How can I reduce the space between images?

The following source code has three problems:

1. it can't show only one image.
2. it doesn't preserve the original aspect ration of images
3. space between images is too wide.

How can I fix these three issues?

draw_multiple_images.m

function draw_multiple_images(image_list)    
    d = size(image_list);
    l = length(d);

      figure;
      hold all
      colormap(gray(256));  

      % vector or cell-array
      if(l==2)
          N = length(image_list);
          [m, n] = factor_out(N);

          % images may be of differenet dimensions
          if(iscell(image_list))    
              for k=1:N
                  h = subplot(m,n,k);
                  image(image_list{k},'Parent',h);
                  set(gca,'xtick',[],'ytick',[])
              end
          % must be of same dimension
          elseif(isvector(image_list))
              for k=1:N
                  h = subplot(m,n,k);
                  image(image_list(k),'Parent',h);
                  set(gca,'xtick',[],'ytick',[])
              end
          end
      % 3D matrix of images (!!!)
      elseif(l==3)
          N = d(3) ;
          [m, n] = factor_out(N);
          for k=1:N
              I = image_list(:,:,k);
              subplot(m,n,k);
              imshow(I);
              set(gca,'xtick',[],'ytick',[])
          end  
      end     
      hold off

function [m, n] = factor_out(input_number)
    sqrtt = ceil(sqrt(input_number));    
    m = sqrtt;
    n = sqrtt;

[Adam]

You are better off creating and positioning your own axes than using subplot for images. subplot leaves a lot of space to allow for things like titles, axes labels, ticks etc, most or all of which you don't want for an image so you just get blank space instead.

doc axes properties

will guide you to settings regarding aspect ratio - DataAspectRatio and PlotBoxAspectRatio in particular.

I don't understand your first point - 'can't only show one image'?

[Ba Ba Black Sheep!]

image_name = 'lena.png';
I = gray_imread(image_name);  
draw_multiple_images(I);

Doesn't show anything.

Answer 1

[Jan]

Use axes image to use the original dimensions.

You can find a lot of tools for adjusting the space between subplots in the FileExchange: FEX: Serach "subplot"

Beside searching in the FileExchange, you can find these solutions by using an internet search engine also.

Please explain "can't show only one image": What input are you using and what do you observe?

[Ba Ba Black Sheep!]

image_name = 'lena.png';
I = gray_imread(image_name);  
draw_multiple_images(I);

Doesn't show anything.

image_name = 'lena.png';
I = gray_imread(image_name);  
N = 12;
J = zeros(size(I,1), size(I,2), N);
for i=1:N    
    J(:,:,i) = I;
end  
draw_multiple_images(J);

Doesn't show anything.

[Jan]

What is "gray_imread"?

[Ba Ba Black Sheep!]

function img = gray_imread( image_name )
    I = imread(image_name);

      if(is_rgb(I))
          img = rgb2gray(I);
      elseif (is_gray(I))
          img = I;
      end    

function ret = is_gray( yourImage )
    [~, ~, numberOfColorChannels] = size(yourImage); 

      if(numberOfColorChannels == 1)
          ret = 1;
      else
          ret = 0;
      end

function ret = is_rgb( a )
    if size(a,3)==3
        ret = 1;
    else
        ret = 0;
    end

[Image Analyst]

Also attach annotated screenshots indicating what you want to be positioned and sized where.