Add pixel-derived image statistics via vips_stats (#915)

src/stats.h

@@ -0,0 +1,65 @@
+// Copyright 2013, 2014, 2015, 2016, 2017 Lovell Fuller and contributors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_STATS_H_
+#define SRC_STATS_H_
+
+#include <string>
+#include <nan.h>
+
+#include "./common.h"
+
+struct ChannelStats {
+  // stats per channel
+  int min;
+  int max;
+  double sum;
+  double squaresSum;
+  double mean;
+  double stdev;
+  int minX;
+  int minY;
+  int maxX;
+  int maxY;
+
+  ChannelStats():
+    min(0), max(0), sum(0), squaresSum(0), mean(0), stdev(0)
+    , minX(0), minY(0), maxX(0), maxY(0) {}
+
+    ChannelStats(int minVal, int maxVal, double sumVal, double squaresSumVal,
+                  double meanVal, double stdevVal, int minXVal, int minYVal, int maxXVal, int maxYVal):
+    min(minVal), max(maxVal), sum(sumVal), squaresSum(squaresSumVal),
+    mean(meanVal), stdev(stdevVal), minX(minXVal), minY(minYVal), maxX(maxXVal), maxY(maxYVal) {}
+};
+
+struct StatsBaton {
+  // Input
+  sharp::InputDescriptor *input;
+  VipsAccess accessMethod;
+
+  // Output
+  std::vector<ChannelStats> channelStats;
+  bool isOpaque;
+
+  std::string err;
+
+  StatsBaton():
+    input(nullptr),
+    isOpaque(true)
+    {}
+};
+
+NAN_METHOD(stats);
+
+#endif  // SRC_STATS_H_