A speed up when subtracting median background from files. Activate with a...

A speed up when subtracting median background from files.  Activate with a flag in parameters for backwards compatibility.

Signed-off-by: Andrew King <andrew.king@esrf.fr>

2_difspot/gtReadAndThreshold.m

@@ -78,12 +78,20 @@ function [img, med_value, info] = gtReadAndThreshold(ndx, parameters, thr_single
         %taken from gtFullStatCondor - thanks Peter!
         nullbb = NaN(seg.bbox(4), seg.bbox(3));
         imn    = gtPlaceSubImage2(nullbb, im_full, seg.bbox(1), seg.bbox(2));
-        imn    = imn(~isnan(imn(:)));
-
+        
+        % can use a sub set of pixel to calculate the median, it's faster
+        if isfield(seg, 'background_subtract_accelerate') && seg.background_subtract_accelerate == true
+            out.fprintf('/// andy speed up by calculating median on subset of pixels ///\n');
+            imn = imn(1:127:end);
+        else
+            % the original routine
+            out.fprintf('subtracting median background value\n');
+        end
+        
+        imn    = imn(~isnan(imn));
         med_value = median(imn);
         im_full   = im_full - med_value;
-
-        out.fprintf('subtracting median background value\n');
+         
     else
         med_value = NaN;
     end