Compute ssim depending on number of output arguments

qualityMetrics.m

-function [psnr_y,ssim_y,psnr_yuv,ssim_yuv,psnr_u,ssim_u,psnr_v,ssim_v] = ...
-    qualityMetrics(rec,ref,varargin)
+function [psnr_y,psnr_yuv,psnr_u,psnr_v,ssim_y,ssim_yuv,ssim_u,ssim_v] = ...
+    qualityMetrics(rec,ref,n,varargin)
 %QUALITYMETRICS Summary of this function goes here
 %   Detailed explanation goes here
 
-if (nargin < 3)
+if ~exist('n','var')
     dr = diff(getrangefromclass(rec));
     n = log2(double(dr)+1);
 else
-    n = varargin{1};
     dr = 2^n-1;
 end
 
+compute_ssim = nargout>4;
+
 numchan = size(rec,3);
 
+ssim_y = nan;
+ssim_yuv = nan;
+ssim_u = nan;
+ssim_v = nan;
+
 if numchan==1
     psnr_y = psnr(rec(:,:,1),ref(:,:,1),dr);
     psnr_u = nan;
@@ -20,14 +26,12 @@ if numchan==1
     
     psnr_yuv = nan;
     
-    ssim_y = ssim(rec(:,:,1),ref(:,:,1),'DynamicRange',dr);
-    ssim_u = nan;
-    ssim_v = nan;
-    
-    ssim_yuv = nan;
+    if compute_ssim
+        ssim_y = ssim(rec(:,:,1),ref(:,:,1),'DynamicRange',dr);
+    end
 elseif numchan==3
-    rec = utils.rgb2ycbcr(rec,n,varargin{2:end});
-    ref = utils.rgb2ycbcr(ref,n,varargin{2:end});
+    rec = utils.rgb2ycbcr(rec,n,varargin{:});
+    ref = utils.rgb2ycbcr(ref,n,varargin{:});
     
     psnr_y = psnr(rec(:,:,1),ref(:,:,1),dr);
     psnr_u = psnr(rec(:,:,2),ref(:,:,2),dr);
@@ -35,11 +39,13 @@ elseif numchan==3
     
     psnr_yuv = (6*psnr_y + psnr_u + psnr_v)/8;
     
-    ssim_y = ssim(rec(:,:,1),ref(:,:,1),'DynamicRange',dr);
-    ssim_u = ssim(rec(:,:,2),ref(:,:,2),'DynamicRange',dr);
-    ssim_v = ssim(rec(:,:,3),ref(:,:,3),'DynamicRange',dr);
-    
-    ssim_yuv = ssim(rec,ref,'DynamicRange',dr);
+    if compute_ssim
+        ssim_y = ssim(rec(:,:,1),ref(:,:,1),'DynamicRange',dr);
+        ssim_u = ssim(rec(:,:,2),ref(:,:,2),'DynamicRange',dr);
+        ssim_v = ssim(rec(:,:,3),ref(:,:,3),'DynamicRange',dr);
+        
+        ssim_yuv = ssim(rec,ref,'DynamicRange',dr);
+    end
 else
     error('Unexpected number of channels');
 end