libcamera: Add support for monochrome sensors

This commit adds support for monochrome (greyscale) raw sensors. These
are sensors that have no colour filter array, so all pixels are the
same and there are no distinct colour channels.

These sensors still require many of an ISP's processing stages, such
as denoise, tone mapping, but not those that involve colours (such as
demosaic, or colour matrices).

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/bayer_format.h

@@ -23,7 +23,8 @@ public:
 		BGGR = 0,
 		GBRG = 1,
 		GRBG = 2,
-		RGGB = 3
+		RGGB = 3,
+		MONO = 4
 	};
 
 	enum Packing : uint16_t {

src/libcamera/bayer_format.cpp

@@ -45,6 +45,8 @@ namespace libcamera {
  * \brief G then R on the first row, B then G on the second row.
  * \var BayerFormat::RGGB
  * \brief R then G on the first row, G then B on the second row.
+ * \var BayerFormat::MONO
+ * \brief Monochrome image data, there is no colour filter array.
  */
 
 /**
@@ -111,6 +113,8 @@ const std::map<BayerFormat, V4L2PixelFormat, BayerFormatComparator> bayerToV4l2{
 	{ { BayerFormat::GBRG, 16, BayerFormat::None }, V4L2PixelFormat(V4L2_PIX_FMT_SGBRG16) },
 	{ { BayerFormat::GRBG, 16, BayerFormat::None }, V4L2PixelFormat(V4L2_PIX_FMT_SGRBG16) },
 	{ { BayerFormat::RGGB, 16, BayerFormat::None }, V4L2PixelFormat(V4L2_PIX_FMT_SRGGB16) },
+	{ { BayerFormat::MONO, 8, BayerFormat::None }, V4L2PixelFormat(V4L2_PIX_FMT_GREY) },
+	{ { BayerFormat::MONO, 10, BayerFormat::CSI2Packed }, V4L2PixelFormat(V4L2_PIX_FMT_Y10P) },
 };
 
 const std::unordered_map<unsigned int, BayerFormat> mbusCodeToBayer{
@@ -146,6 +150,8 @@ const std::unordered_map<unsigned int, BayerFormat> mbusCodeToBayer{
 	{ MEDIA_BUS_FMT_SGBRG16_1X16, { BayerFormat::GBRG, 16, BayerFormat::None } },
 	{ MEDIA_BUS_FMT_SGRBG16_1X16, { BayerFormat::GRBG, 16, BayerFormat::None } },
 	{ MEDIA_BUS_FMT_SRGGB16_1X16, { BayerFormat::RGGB, 16, BayerFormat::None } },
+	{ MEDIA_BUS_FMT_Y8_1X8, { BayerFormat::MONO, 8, BayerFormat::None } },
+	{ MEDIA_BUS_FMT_Y10_1X10, { BayerFormat::MONO, 10, BayerFormat::None } },
 };
 
 } /* namespace */
@@ -198,9 +204,10 @@ std::string BayerFormat::toString() const
 		"BGGR",
 		"GBRG",
 		"GRBG",
-		"RGGB"
+		"RGGB",
+		"MONO"
 	};
-	if (isValid() && order <= RGGB)
+	if (isValid() && order <= MONO)
 		result = orderStrings[order];
 	else
 		return "INVALID";
@@ -280,6 +287,9 @@ BayerFormat BayerFormat::transform(Transform t) const
 {
 	BayerFormat result = *this;
 
+	if (order == MONO)
+		return result;
+
 	/*
 	 * Observe that flipping bit 0 of the Order enum performs a horizontal
 	 * mirror on the Bayer pattern (e.g. RGGB goes to GRBG). Similarly,

src/libcamera/camera_sensor.cpp

@@ -428,6 +428,9 @@ int CameraSensor::initProperties()
 		case BayerFormat::RGGB:
 			cfa = properties::draft::RGGB;
 			break;
+		case BayerFormat::MONO:
+			cfa = properties::draft::MONO;
+			break;
 		}
 
 		properties_.set(properties::draft::ColorFilterArrangement, cfa);

src/libcamera/property_ids.yaml

@@ -706,5 +706,9 @@ controls:
           description: |
             Sensor is not Bayer; output has 3 16-bit values for each pixel,
             instead of just 1 16-bit value per pixel.
+        - name: MONO
+          value: 5
+          description: |
+            Sensor is not Bayer; output consists of a single colour channel.
 
 ...