JFJochReaderImage: Add function to develop auto-contrast, still need to connect it to the right place

reader/JFJochReaderImage.cpp

@@ -247,3 +247,14 @@ std::shared_ptr<JFJochReaderDataset> JFJochReaderImage::CreateMutableDataset() {
     dataset = new_dataset;
     return new_dataset;
 }
+
+int32_t JFJochReaderImage::GetAutoContrastValue(float range) const {
+    if (valid_pixel.empty())
+        return 10;
+
+    auto it = valid_pixel.begin();
+    const auto index = static_cast<size_t>(valid_pixel.size() * range);
+
+    std::advance(it, std::max<size_t>(1ULL, index) - 1);
+    return std::max(1, it->first);
+}

reader/JFJochReaderImage.h

@@ -53,6 +53,8 @@ public:
     void CalcROI(const ROIElement *input);
 
     std::shared_ptr<JFJochReaderDataset> CreateMutableDataset();
+
+    int32_t GetAutoContrastValue(float range = 0.95f) const;
 };
 
 #endif //JFJOCH_JFJOCHREADERIMAGE_H