diff --git a/MUNGA_L4/L4VB16.cpp b/MUNGA_L4/L4VB16.cpp
index cbf0f3f..9f4c268 100644
--- a/MUNGA_L4/L4VB16.cpp
+++ b/MUNGA_L4/L4VB16.cpp
@@ -5202,6 +5202,43 @@ Logical SVGA16::Update(Logical forceAll)
 				int src_w = pixelBuffer.Data.Size.x;
 				int src_h = pixelBuffer.Data.Size.y;
 
+				//
+				// RP412CAMLOG. A camera's map showed content at mission
+				// start and then went black, which is three different
+				// faults wearing one symptom: the copy stopping, the
+				// SOURCE canvas going blank, or the pane not repainting.
+				// Counting non-zero source pixels as we pass tells them
+				// apart - a live canvas with a black pane is the third,
+				// a blank canvas is the second, and no line at all is the
+				// first. Every five seconds; the count is a sample of one
+				// row in sixteen, which is plenty to tell blank from not.
+				//
+				if (RPCameraLog())
+				{
+					static Scalar next_copy_say = 0.0f;
+					if ((Scalar) Now() >= next_copy_say)
+					{
+						next_copy_say = ((Scalar) Now()) + 5.0f;
+
+						long lit = 0;
+						for (int sy = 0; sy < src_h; sy += 16)
+						{
+							Word *row = source_base + sy * src_w;
+							for (int sx = 0; sx < src_w; ++sx)
+							{
+								if (row[sx] != 0)
+								{
+									++lit;
+								}
+							}
+						}
+						DEBUG_STREAM << "CamLog: map copy running, source "
+							<< src_w << "x" << src_h << ", " << lit
+							<< " lit pixels sampled, mask 0x" << std::hex
+							<< secMask << std::dec << "\n" << std::flush;
+					}
+				}
+
 				if (Application::IsCameraStation())
 				{
 					//