CvSink: Support grayscale images.

Also support 4-channel BGRx images and provide better error reporting
on bad images passed to PutFrame.

java/src/edu/wpi/cscore/CvSink.java

@@ -39,6 +39,7 @@ public class CvSink extends VideoSink {
   }
 
   /// Wait for the next frame and get the image.
+  /// The provided image will have three 3-bit channels stored in BGR order.
   /// @return Frame time, or 0 on error (call GetError() to obtain the error
   ///         message);
   public long grabFrame(Mat image) {

java/src/edu/wpi/cscore/CvSource.java

@@ -29,6 +29,9 @@ public class CvSource extends VideoSource {
   }
 
   /// Put an OpenCV image and notify sinks.
+  /// Only 8-bit single-channel or 3-channel (with BGR channel order) images
+  /// are supported. If the format, depth or channel order is different, use
+  /// Mat.convertTo() and/or cvtColor() to convert it first.
   /// @param image OpenCV image
   public void putFrame(Mat image) {
     CameraServerJNI.putSourceFrame(m_handle, image.nativeObj);

java/src/edu/wpi/cscore/VideoMode.java

@@ -10,7 +10,7 @@ package edu.wpi.cscore;
 /// Video mode
 public class VideoMode {
   public enum PixelFormat {
-    kUnknown(0), kMJPEG(1), kYUYV(2), kRGB565(3), kBGR(4);
+    kUnknown(0), kMJPEG(1), kYUYV(2), kRGB565(3), kBGR(4), kGray(5);
     private int value;
 
     private PixelFormat(int value) {