Using MATLAB for median, quartil, interquartil span and resolution.

0 down vote favorite I have a picture in MATLAB and decompositioned it to R, G and B channel. And now I need to figure out resolution, median, upper and lower quartil, interquartil span and modus.

Here is the code I use for it:

 I = imread('image_S006_I0000.jpg'); 
 imshow(I)                           

 [R S T] = size(I);                  

 Red(:,:,1)=I(:,:,1);
 Red(:,:,2)=zeros(R,S);
 Red(:,:,3)=zeros(R,S);

 Green(:,:,1)=zeros(R,S);
 Green(:,:,2)=I(:,:,1);
 Green(:,:,3)=zeros(R,S);

 Blue(:,:,1)=zeros(R,S);
 Blue(:,:,2)=zeros(R,S);
 Blue(:,:,3)=I(:,:,1);

 [x1 y1 z1] = size(I);   

 % MEDIAN. 
 imgmedianR = median (Red(:))
 imgmedianG = median (Green(:))
 imgmedianB = median (Blue(:))

 %QUARTIL
 r025 = quantile(Red,0.25) 
 r075 = quantile(Red,0.75) 

 g025 = quantile(Green,0.25) 
 g075 = quantile(Green,0.75) 

 b025 = quantile(Blue,0.25) 
 b075 = quantile(Blue,0.75) 

 %INTERQUARTIL SPAN
 r_iqr = iqr(Red) 
 g_iqr = iqr(Green) 
 b_iqr = iqr(Blue) 

 modus_Red = mode(Red(:))
 modus_Green = mode(Green(:))
 modus_Blue = mode(Blue(:))

MEDIAN: When I try to count MEDIAN, it gives me a bunch of numbers (actually matlab prints out a number for each column separately). I need one number only. What have I done wrong there?

QUARTIL: The same problem as I have in code for MEDIAN. I need one number only. What have I done wrong there?

INTERQUARTIL SPAN: Matlab prints out subsequent error: Mixed integer class inputs are not supported. What have I done wrong?

RESOLUTION: I need to find out a resolution of the image using Matlab. I have tried out funciton imfinfo, but the info isn't included. How can I find such an information using any kind of Matlab function?

Thank you very much in advance!