Enhance NV12 and NV21 Support in sensor_msgs::image_encodings (#264)

- Redefine numChannels for NV12 and NV21 from 2 to 1 to accurately reflect their planar YUV 4:2:0 format.
- Add isPlanar function to determine if an encoding is planar (e.g., NV12, NV21, NV24).
- Introduce getHeightScaling function to provide height scaling factors for planar encodings.
- Improve code consistency and add documentation for new utility functions.

Signed-off-by: Zhaoyuan Cheng <zycczyby@gmail.com>

Author: zycczy

sensor_msgs/include/sensor_msgs/image_encodings.hpp

@@ -150,6 +150,11 @@ static inline bool hasAlpha(const std::string & encoding)
          encoding == RGBA16 || encoding == BGRA16;
 }
 
+static inline bool isPlanar(const std::string & encoding)
+{
+  return encoding == NV12 || encoding == NV21 || encoding == NV24;
+}
+
 static inline int numChannels(const std::string & encoding)
 {
   // First do the common-case encodings
@@ -191,12 +196,15 @@ static inline int numChannels(const std::string & encoding)
     return (m[3] == "") ? 1 : std::atoi(m[3].str().c_str());
   }
 
+  if (encoding == NV12 ||
+    encoding == NV21)
+  {
+    return 1;
+  }
   if (encoding == YUV422 ||
     encoding == YUV422_YUY2 ||
     encoding == UYVY ||
     encoding == YUYV ||
-    encoding == NV12 ||
-    encoding == NV21 ||
     encoding == NV24)
   {
     return 2;
@@ -258,6 +266,19 @@ static inline int bitDepth(const std::string & encoding)
   throw std::runtime_error("Unknown encoding " + encoding);
   return -1;
 }
+
+static inline float getHeightScaling(const std::string & encoding)
+{
+  if (isPlanar(encoding)) {
+    if (encoding == NV12 ||
+      encoding == NV21)
+    {
+      return 1.5f;
+    }
+  }
+  return 1.0f;
+}
+
 }  // namespace image_encodings
 }  // namespace sensor_msgs
 

sensor_msgs/test/test_image_encodings.cpp

@@ -71,3 +71,25 @@ TEST(sensor_msgs, bitDepth)
   ASSERT_EQ(sensor_msgs::image_encodings::bitDepth("yuv422"), 8);
   ASSERT_EQ(sensor_msgs::image_encodings::bitDepth("yuv422_yuy2"), 8);
 }
+
+TEST(sensor_msgs, getHeightScaling)
+{
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("nv12"), 1.5f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("nv21"), 1.5f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("mono8"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("rgb8"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("8UC"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("8UC3"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("8UC10"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("16UC"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("16UC3"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("16UC10"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("32SC"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("32SC3"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("32SC10"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("64FC"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("64FC3"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("64FC10"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("yuv422"), 1.0f);
+  ASSERT_FLOAT_EQ(sensor_msgs::image_encodings::getHeightScaling("yuv422_yuy2"), 1.0f);
+}