detector l2 norm weight default structure.

Signed-off-by: Zheheng Liu <zheheng.liu@esrf.fr>

5_reconstruction/gtRecGrainsOptionsDetectorL2NormWeightDefaultParameters.m

+function detector_l2_norm_weight = gtRecGrainsOptionsDetectorL2NormWeightDefaultParameters(weight_type, weight_coef, acq)
+    possible_weight_types = {'linear','sqrt','log'};
+    if ((~exist('weight_type', 'var')) || (~ismember(lower(weight_type), possible_weight_types)))
+        detector_l2_norm_weight = [];
+    else
+        weight_type = lower(weight_type);
+        if ((~exist('weight_coef', 'var')) || isempty(weight_coef) || (~isnumeric(weight_coef)))
+            if (~exist('acq', 'var') || isempty(acq))
+                acq = gtLoadParameters;
+                acq = acq.acq;
+            end
+            weight_coef = sfCalcDarkImagesVariance(acq);
+        else
+            weight_coef = weight_coef(1);
+        end
+        detector_l2_norm_weight = struct('type', weight_type, 'coefficient', weight_coef);
+    end
+end
+
+function noise_var = sfCalcDarkImagesVariance(acq)
+    darkend = cell(1, acq.ndark);
+    for ii_dark = 1:acq.ndark
+        darkname = fullfile(acq.dir,'0_rawdata',acq.name,sprintf('darkend%04d.edf', ii_dark-1));
+        darkend{ii_dark} = edf_read(darkname);
+    end
+    darkend = cat(3, darkend{:});
+    dark = sum(darkend, 3) / acq.ndark;
+    darkend = bsxfun(@minus, darkend, dark);
+    noise_var = sum(darkend(:) .^ 2) / numel(dark(:)) / (acq.ndark - 1);
+end
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