Various fixes to XYZ/RGB transforms.

16 files changed, 130 insertions, 92 deletions

diff --git a/src/colour_conversion.cc b/src/colour_conversion.cc
index 28edf9bc..f2e85e76 100644
--- a/src/colour_conversion.cc
+++ b/src/colour_conversion.cc
@@ -26,22 +26,21 @@ using boost::shared_ptr;
 using namespace dcp;
 
 ColourConversion ColourConversion::srgb_to_xyz (
-	shared_ptr<const TransferFunction> (new ModifiedGammaTransferFunction (2.4, 0.04045, 0.055, 12.92)),
+	shared_ptr<const TransferFunction> (new ModifiedGammaTransferFunction (false, 2.4, 0.04045, 0.055, 12.92)),
 	dcp::colour_matrix::srgb_to_xyz,
-	shared_ptr<const TransferFunction> (new GammaTransferFunction (2.6))
+	shared_ptr<const TransferFunction> (new GammaTransferFunction (true, 2.6))
 	);
 
-/* XXX: what sort of RGB is this...? */
-ColourConversion ColourConversion::xyz_to_rgb (
-	shared_ptr<const TransferFunction> (new GammaTransferFunction (2.6)),
+ColourConversion ColourConversion::xyz_to_srgb (
+	shared_ptr<const TransferFunction> (new GammaTransferFunction (false, 2.6)),
 	dcp::colour_matrix::xyz_to_rgb,
-	shared_ptr<const TransferFunction> (new GammaTransferFunction (2.2))
+	shared_ptr<const TransferFunction> (new ModifiedGammaTransferFunction (true, 2.4, 0.04045, 0.055, 12.92))
 	);
 
 ColourConversion ColourConversion::rec709_to_xyz (
-	shared_ptr<const TransferFunction> (new ModifiedGammaTransferFunction (2.4, 0.081, 0.099, 4.5)),
+	shared_ptr<const TransferFunction> (new ModifiedGammaTransferFunction (false, 2.4, 0.081, 0.099, 4.5)),
 	dcp::colour_matrix::srgb_to_xyz,
-	shared_ptr<const TransferFunction> (new GammaTransferFunction (2.6))
+	shared_ptr<const TransferFunction> (new GammaTransferFunction (true, 2.6))
 	);
 
 ColourConversion::ColourConversion (
diff --git a/src/colour_conversion.h b/src/colour_conversion.h
index 9bb7c6ee..e2a8c6bc 100644
--- a/src/colour_conversion.h
+++ b/src/colour_conversion.h
@@ -64,7 +64,7 @@ public:
 	bool about_equal (ColourConversion const & other, float epsilon) const;
 
 	static ColourConversion srgb_to_xyz;
-	static ColourConversion xyz_to_rgb;
+	static ColourConversion xyz_to_srgb;
 	static ColourConversion rec709_to_xyz;
 
 protected:
diff --git a/src/gamma_transfer_function.cc b/src/gamma_transfer_function.cc
index b4aa20f1..9d5ceba4 100644
--- a/src/gamma_transfer_function.cc
+++ b/src/gamma_transfer_function.cc
@@ -25,27 +25,33 @@ using boost::shared_ptr;
 using boost::dynamic_pointer_cast;
 using namespace dcp;
 
-GammaTransferFunction::GammaTransferFunction (float gamma)
-	: _gamma (gamma)
+GammaTransferFunction::GammaTransferFunction (bool inverse, double gamma)
+	: TransferFunction (inverse)
+	, _gamma (gamma)
 {
 
 }
 
-float *
+double *
 GammaTransferFunction::make_lut (int bit_depth) const
 {
 	int const bit_length = pow (2, bit_depth);
-	float* lut = new float[int(std::pow(2.0f, bit_depth))];
+	double* lut = new double[int(std::pow(2.0f, bit_depth))];
+	double const gamma = _inverse ? (1 / _gamma) : _gamma;
 	for (int i = 0; i < bit_length; ++i) {
-		lut[i] = pow(float(i) / (bit_length - 1), _gamma);
+		lut[i] = pow(double(i) / (bit_length - 1), gamma);
 	}
 
 	return lut;
 }
 
 bool
-GammaTransferFunction::about_equal (shared_ptr<const TransferFunction> other, float epsilon) const
+GammaTransferFunction::about_equal (shared_ptr<const TransferFunction> other, double epsilon) const
 {
+	if (!TransferFunction::about_equal (other, epsilon)) {
+		return false;
+	}
+	
 	shared_ptr<const GammaTransferFunction> o = dynamic_pointer_cast<const GammaTransferFunction> (other);
 	if (!o) {
 		return false;
diff --git a/src/gamma_transfer_function.h b/src/gamma_transfer_function.h
index 85035f66..17efe12e 100644
--- a/src/gamma_transfer_function.h
+++ b/src/gamma_transfer_function.h
@@ -24,19 +24,19 @@ namespace dcp {
 class GammaTransferFunction : public TransferFunction
 {
 public:
-	GammaTransferFunction (float gamma);
+	GammaTransferFunction (bool inverse, double gamma);
 
-	float gamma () const {
+	double gamma () const {
 		return _gamma;
 	}
 
-	bool about_equal (boost::shared_ptr<const TransferFunction> other, float epsilon) const;
+	bool about_equal (boost::shared_ptr<const TransferFunction> other, double epsilon) const;
 
 protected:
-	float * make_lut (int bit_depth) const;
+	double * make_lut (int bit_depth) const;
 
 private:
-	float _gamma;
+	double _gamma;
 };
 
 }
diff --git a/src/image.h b/src/image.h
index 941325cd..abc040d4 100644
--- a/src/image.h
+++ b/src/image.h
@@ -29,8 +29,9 @@ public:
 	Image (boost::shared_ptr<const Image>);
 	
 	virtual ~Image () {}
-	virtual uint8_t** data () const = 0;
-	virtual int* stride () const = 0;
+	virtual uint16_t * const * data () const = 0;
+	/** @return array of strides in bytes */
+	virtual int const * stride () const = 0;
 
 	Size size () const {
 		return _size;
diff --git a/src/modified_gamma_transfer_function.cc b/src/modified_gamma_transfer_function.cc
index 7878773b..ef4bb225 100644
--- a/src/modified_gamma_transfer_function.cc
+++ b/src/modified_gamma_transfer_function.cc
@@ -25,8 +25,9 @@ using boost::shared_ptr;
 using boost::dynamic_pointer_cast;
 using namespace dcp;
 
-ModifiedGammaTransferFunction::ModifiedGammaTransferFunction (float power, float threshold, float A, float B)
-	: _power (power)
+ModifiedGammaTransferFunction::ModifiedGammaTransferFunction (bool inverse, double power, double threshold, double A, double B)
+	: TransferFunction (inverse)
+	, _power (power)
 	, _threshold (threshold)
 	, _A (A)
 	, _B (B)
@@ -34,17 +35,29 @@ ModifiedGammaTransferFunction::ModifiedGammaTransferFunction (float power, float
 
 }
 
-float *
+double *
 ModifiedGammaTransferFunction::make_lut (int bit_depth) const
 {
 	int const bit_length = pow (2, bit_depth);
-	float* lut = new float[int(std::pow(2.0f, bit_depth))];
-	for (int i = 0; i < bit_length; ++i) {
-		float const p = static_cast<float> (i) / (bit_length - 1);
-		if (p > _threshold) {
-			lut[i] = pow ((p + _A) / (1 + _A), _power);
-		} else {
-			lut[i] = p / _B;
+	double* lut = new double[int(std::pow(2.0f, bit_depth))];
+	if (_inverse) {
+		double const threshold = _threshold / _B;
+		for (int i = 0; i < bit_length; ++i) {
+			double const p = static_cast<double> (i) / (bit_length - 1);
+			if (p > threshold) {
+				lut[i] = (1 + _A) * pow (p, 1 / _power) - _A;
+			} else {
+				lut[i] = p * _B;
+			}
+		}
+	} else {
+		for (int i = 0; i < bit_length; ++i) {
+			double const p = static_cast<double> (i) / (bit_length - 1);
+			if (p > _threshold) {
+				lut[i] = pow ((p + _A) / (1 + _A), _power);
+			} else {
+				lut[i] = p / _B;
+			}
 		}
 	}
 
@@ -52,8 +65,12 @@ ModifiedGammaTransferFunction::make_lut (int bit_depth) const
 }
 
 bool
-ModifiedGammaTransferFunction::about_equal (shared_ptr<const TransferFunction> other, float epsilon) const
+ModifiedGammaTransferFunction::about_equal (shared_ptr<const TransferFunction> other, double epsilon) const
 {
+	if (!TransferFunction::about_equal (other, epsilon)) {
+		return false;
+	}
+	
 	shared_ptr<const ModifiedGammaTransferFunction> o = dynamic_pointer_cast<const ModifiedGammaTransferFunction> (other);
 	if (!o) {
 		return false;
diff --git a/src/modified_gamma_transfer_function.h b/src/modified_gamma_transfer_function.h
index 0c6a6b84..aec52de7 100644
--- a/src/modified_gamma_transfer_function.h
+++ b/src/modified_gamma_transfer_function.h
@@ -29,34 +29,34 @@ namespace dcp {
 class ModifiedGammaTransferFunction : public TransferFunction
 {
 public:
-	ModifiedGammaTransferFunction (float power, float threshold, float A, float B);
+	ModifiedGammaTransferFunction (bool inverse, double power, double threshold, double A, double B);
 
-	float power () const {
+	double power () const {
 		return _power;
 	}
 
-	float threshold () const {
+	double threshold () const {
 		return _threshold;
 	}
 
-	float A () const {
+	double A () const {
 		return _A;
 	}
 
-	float B () const {
+	double B () const {
 		return _B;
 	}
 
-	bool about_equal (boost::shared_ptr<const TransferFunction>, float epsilon) const;
+	bool about_equal (boost::shared_ptr<const TransferFunction>, double epsilon) const;
 	
 protected:
-	float * make_lut (int bit_depth) const;
+	double * make_lut (int bit_depth) const;
 	
 private:
-	float _power;
-	float _threshold;
-	float _A;
-	float _B;
+	double _power;
+	double _threshold;
+	double _A;
+	double _B;
 };
 
 }
diff --git a/src/mono_picture_frame.cc b/src/mono_picture_frame.cc
index 31499c64..4fe9356c 100644
--- a/src/mono_picture_frame.cc
+++ b/src/mono_picture_frame.cc
@@ -123,16 +123,16 @@ MonoPictureFrame::argb_frame (int reduce, float srgb_gamma) const
 {
 	return xyz_to_rgba (
 		decompress_j2k (const_cast<uint8_t*> (_buffer->RoData()), _buffer->Size(), reduce),
-		ColourConversion::xyz_to_rgb
+		ColourConversion::xyz_to_srgb
 		);
 }
 
 void
-MonoPictureFrame::rgb_frame (uint8_t* buffer) const
+MonoPictureFrame::rgb_frame (uint16_t* buffer) const
 {
 	xyz_to_rgb (
 		decompress_j2k (const_cast<uint8_t*> (_buffer->RoData()), _buffer->Size(), 0),
-		ColourConversion::xyz_to_rgb,
+		ColourConversion::xyz_to_srgb,
 		buffer
 		);
 }
diff --git a/src/mono_picture_frame.h b/src/mono_picture_frame.h
index 78728fbf..50ea0891 100644
--- a/src/mono_picture_frame.h
+++ b/src/mono_picture_frame.h
@@ -51,7 +51,7 @@ public:
 	~MonoPictureFrame ();
 
 	boost::shared_ptr<ARGBFrame> argb_frame (int reduce = 0, float srgb_gamma = 2.4) const;
-	void rgb_frame (uint8_t* buffer) const;
+	void rgb_frame (uint16_t* buffer) const;
 	uint8_t const * j2k_data () const;
 	uint8_t* j2k_data ();
 	int j2k_size () const;
diff --git a/src/rgb_xyz.cc b/src/rgb_xyz.cc
index 35332fc2..faddf013 100644
--- a/src/rgb_xyz.cc
+++ b/src/rgb_xyz.cc
@@ -61,8 +61,8 @@ dcp::xyz_to_rgba (
 	shared_ptr<ARGBFrame> argb_frame (new ARGBFrame (xyz_frame->size ()));
 	uint8_t* argb = argb_frame->data ();
 	
-	float const * lut_in = conversion.in()->lut (16);
-	float const * lut_out = conversion.out()->lut (12);
+	double const * lut_in = conversion.in()->lut (16);
+	double const * lut_out = conversion.out()->lut (12);
 	boost::numeric::ublas::matrix<double> matrix = conversion.matrix ();
 
 	for (int y = 0; y < xyz_frame->size().height; ++y) {
@@ -96,9 +96,9 @@ dcp::xyz_to_rgba (
 			d.b = max (d.b, 0.0);
 			
 			/* Out gamma LUT */
-			*argb_line++ = lut_out[(int) (d.b * max_colour)] * 0xff;
-			*argb_line++ = lut_out[(int) (d.g * max_colour)] * 0xff;
-			*argb_line++ = lut_out[(int) (d.r * max_colour)] * 0xff;
+			*argb_line++ = lut_out[int(rint(d.b * max_colour))] * 0xff;
+			*argb_line++ = lut_out[int(rint(d.g * max_colour))] * 0xff;
+			*argb_line++ = lut_out[int(rint(d.r * max_colour))] * 0xff;
 			*argb_line++ = 0xff;
 		}
 		
@@ -110,21 +110,18 @@ dcp::xyz_to_rgba (
 
 /** Convert an openjpeg XYZ image to RGB.
  *  @param xyz_frame Frame in XYZ.
- *  @param lut_in Input Gamma LUT to use.
- *  @param lut_out Output Gamma LUT to use.
- *  @param buffer Buffer to write RGB data to; will be written
- *  as one byte R, one byte G, one byte B, one byte R etc. with
- *  no padding at line ends.
+ *  @param conversion Colour conversion to use.
+ *  @param buffer Buffer to write RGB data to; rgb will be packed RGB
+ *  16:16:16, 48bpp, 16R, 16G, 16B, with the 2-byte value for each
+ *  R/G/B component stored as little-endian; i.e. AV_PIX_FMT_RGB48LE.
  */
 void
 dcp::xyz_to_rgb (
 	boost::shared_ptr<const XYZFrame> xyz_frame,
 	ColourConversion const & conversion,
-	uint8_t* buffer
+	uint16_t* buffer
 	)
 {
-	int const max_colour = pow (2, 12) - 1;
-
 	struct {
 		double x, y, z;
 	} s;
@@ -132,21 +129,22 @@ dcp::xyz_to_rgb (
 	struct {
 		double r, g, b;
 	} d;
-	
+
+	/* These should be 12-bit values from 0-4095 */
 	int* xyz_x = xyz_frame->data (0);
 	int* xyz_y = xyz_frame->data (1);
 	int* xyz_z = xyz_frame->data (2);
 
-	float const * lut_in = conversion.in()->lut (16);
-	float const * lut_out = conversion.out()->lut (12);
+	double const * lut_in = conversion.in()->lut (12);
+	double const * lut_out = conversion.out()->lut (16);
 	boost::numeric::ublas::matrix<double> matrix = conversion.matrix ();
 	
 	for (int y = 0; y < xyz_frame->size().height; ++y) {
-		uint8_t* buffer_line = buffer;
+		uint16_t* buffer_line = buffer;
 		for (int x = 0; x < xyz_frame->size().width; ++x) {
 
 			DCP_ASSERT (*xyz_x >= 0 && *xyz_y >= 0 && *xyz_z >= 0 && *xyz_x < 4096 && *xyz_y < 4096 && *xyz_z < 4096);
-			
+
 			/* In gamma LUT */
 			s.x = lut_in[*xyz_x++];
 			s.y = lut_in[*xyz_y++];
@@ -170,11 +168,10 @@ dcp::xyz_to_rgb (
 			
 			d.b = min (d.b, 1.0);
 			d.b = max (d.b, 0.0);
-			
-			/* Out gamma LUT */
-			*buffer_line++ = lut_out[(int) (d.r * max_colour)] * 0xff;
-			*buffer_line++ = lut_out[(int) (d.g * max_colour)] * 0xff;
-			*buffer_line++ = lut_out[(int) (d.b * max_colour)] * 0xff;
+
+			*buffer_line++ = rint(lut_out[int(rint(d.r * 65535))] * 65535);
+			*buffer_line++ = rint(lut_out[int(rint(d.g * 65535))] * 65535);
+			*buffer_line++ = rint(lut_out[int(rint(d.b * 65535))] * 65535);
 		}
 		
 		buffer += xyz_frame->size().width * 3;
@@ -200,20 +197,20 @@ dcp::rgb_to_xyz (
 		double x, y, z;
 	} d;
 
-	float const * lut_in = conversion.in()->lut (12);
-	float const * lut_out = conversion.out()->lut (16);
+	double const * lut_in = conversion.in()->lut (12);
+	double const * lut_out = conversion.out()->lut (16);
 	boost::numeric::ublas::matrix<double> matrix = conversion.matrix ();
 
 	int jn = 0;
 	for (int y = 0; y < rgb->size().height; ++y) {
-		uint16_t* p = reinterpret_cast<uint16_t *> (rgb->data()[0] + y * rgb->stride()[0]);
+		uint16_t* p = rgb->data()[0] + y * rgb->stride()[0] / 2;
 		for (int x = 0; x < rgb->size().width; ++x) {
 
 			/* In gamma LUT (converting 16-bit to 12-bit) */
 			s.r = lut_in[*p++ >> 4];
 			s.g = lut_in[*p++ >> 4];
 			s.b = lut_in[*p++ >> 4];
-			
+
 			/* RGB to XYZ Matrix */
 			d.x = ((s.r * matrix(0, 0)) + (s.g * matrix(0, 1)) + (s.b * matrix(0, 2)));
 			d.y = ((s.r * matrix(1, 0)) + (s.g * matrix(1, 1)) + (s.b * matrix(1, 2)));
@@ -229,9 +226,9 @@ dcp::rgb_to_xyz (
 			DCP_ASSERT (d.z >= 0 && d.z < 65536);
 			
 			/* Out gamma LUT */
-			xyz->data(0)[jn] = lut_out[(int) d.x] * 4096;
-			xyz->data(1)[jn] = lut_out[(int) d.y] * 4096;
-			xyz->data(2)[jn] = lut_out[(int) d.z] * 4096;
+			xyz->data(0)[jn] = lut_out[int(rint(d.x))] * 4095;
+			xyz->data(1)[jn] = lut_out[int(rint(d.y))] * 4095;
+			xyz->data(2)[jn] = lut_out[int(rint(d.z))] * 4095;
 
 			++jn;
 		}
@@ -251,7 +248,7 @@ dcp::xyz_to_xyz (shared_ptr<const Image> xyz_16)
 
 	int jn = 0;
 	for (int y = 0; y < xyz_16->size().height; ++y) {
-		uint16_t* p = reinterpret_cast<uint16_t *> (xyz_16->data()[0] + y * xyz_16->stride()[0]);
+		uint16_t* p = xyz_16->data()[0] + y * xyz_16->stride()[0] / 2;
 		for (int x = 0; x < xyz_16->size().width; ++x) {
 			/* Truncate 16-bit to 12-bit */
 			xyz_12->data(0)[jn] = *p++ >> 4;
diff --git a/src/rgb_xyz.h b/src/rgb_xyz.h
index a6463b0d..4dd25b28 100644
--- a/src/rgb_xyz.h
+++ b/src/rgb_xyz.h
@@ -28,7 +28,7 @@ class Image;
 class ColourConversion;
 	
 extern boost::shared_ptr<ARGBFrame> xyz_to_rgba (boost::shared_ptr<const XYZFrame>, ColourConversion const & conversion);
-extern void xyz_to_rgb (boost::shared_ptr<const XYZFrame>, ColourConversion const & conversion, uint8_t* buffer);
+extern void xyz_to_rgb (boost::shared_ptr<const XYZFrame>, ColourConversion const & conversion, uint16_t* buffer);
 extern boost::shared_ptr<XYZFrame> rgb_to_xyz (boost::shared_ptr<const Image>, ColourConversion const & conversion);
 extern boost::shared_ptr<XYZFrame> xyz_to_xyz (boost::shared_ptr<const Image>);
 	
diff --git a/src/stereo_picture_frame.cc b/src/stereo_picture_frame.cc
index 7d989777..3e872e2b 100644
--- a/src/stereo_picture_frame.cc
+++ b/src/stereo_picture_frame.cc
@@ -89,11 +89,11 @@ StereoPictureFrame::argb_frame (Eye eye, int reduce, float srgb_gamma) const
 		break;
 	}
 	
-	return xyz_to_rgba (xyz_frame, ColourConversion::xyz_to_rgb);
+	return xyz_to_rgba (xyz_frame, ColourConversion::xyz_to_srgb);
 }
 
 void
-StereoPictureFrame::rgb_frame (Eye eye, uint8_t* buffer) const
+StereoPictureFrame::rgb_frame (Eye eye, uint16_t* buffer) const
 {
 	shared_ptr<XYZFrame> xyz_frame;
 	switch (eye) {
@@ -105,7 +105,7 @@ StereoPictureFrame::rgb_frame (Eye eye, uint8_t* buffer) const
 		break;
 	}
 	
-	return xyz_to_rgb (xyz_frame, ColourConversion::xyz_to_rgb, buffer);
+	return xyz_to_rgb (xyz_frame, ColourConversion::xyz_to_srgb, buffer);
 }
 
 uint8_t const *
diff --git a/src/stereo_picture_frame.h b/src/stereo_picture_frame.h
index 578bb3de..e8ef689d 100644
--- a/src/stereo_picture_frame.h
+++ b/src/stereo_picture_frame.h
@@ -44,7 +44,7 @@ public:
 	~StereoPictureFrame ();
 
 	boost::shared_ptr<ARGBFrame> argb_frame (Eye eye, int reduce = 0, float srgb_gamma = 2.4) const;
-	void rgb_frame (Eye eye, uint8_t* buffer) const;
+	void rgb_frame (Eye eye, uint16_t* buffer) const;
 	uint8_t const * left_j2k_data () const;
 	uint8_t* left_j2k_data ();
 	int left_j2k_size () const;
diff --git a/src/transfer_function.cc b/src/transfer_function.cc
index 2c7e3e52..d889cbbc 100644
--- a/src/transfer_function.cc
+++ b/src/transfer_function.cc
@@ -22,21 +22,28 @@
 
 using std::pow;
 using std::map;
+using boost::shared_ptr;
 using namespace dcp;
 
+TransferFunction::TransferFunction (bool inverse)
+	: _inverse (inverse)
+{
+
+}
+
 TransferFunction::~TransferFunction ()
 {
-	for (map<int, float*>::const_iterator i = _luts.begin(); i != _luts.end(); ++i) {
+	for (map<int, double*>::const_iterator i = _luts.begin(); i != _luts.end(); ++i) {
 		delete[] i->second;
 	}
 
 	_luts.clear ();
 }
 
-float const *
+double const *
 TransferFunction::lut (int bit_depth) const
 {
-	map<int, float*>::const_iterator i = _luts.find (bit_depth);
+	map<int, double*>::const_iterator i = _luts.find (bit_depth);
 	if (i != _luts.end ()) {
 		return i->second;
 	}
@@ -44,3 +51,9 @@ TransferFunction::lut (int bit_depth) const
 	_luts[bit_depth] = make_lut (bit_depth);
 	return _luts[bit_depth];
 }
+
+bool
+TransferFunction::about_equal (shared_ptr<const TransferFunction> other, double) const
+{
+	return _inverse == other->_inverse;
+}
diff --git a/src/transfer_function.h b/src/transfer_function.h
index 31a794e2..16d00c1a 100644
--- a/src/transfer_function.h
+++ b/src/transfer_function.h
@@ -29,17 +29,22 @@ namespace dcp {
 class TransferFunction : public boost::noncopyable
 {
 public:
+	TransferFunction (bool inverse);
+	
 	virtual ~TransferFunction ();
 
-	float const * lut (int bit_depth) const;
+	/** @return A look-up table (of size 2^bit_depth) whose values range from 0 to 1 */
+	double const * lut (int bit_depth) const;
 
-	virtual bool about_equal (boost::shared_ptr<const TransferFunction> other, float epsilon) const = 0;
+	virtual bool about_equal (boost::shared_ptr<const TransferFunction> other, double epsilon) const;
 
 protected:
-	virtual float * make_lut (int bit_depth) const = 0;
+	virtual double * make_lut (int bit_depth) const = 0;
+
+	bool _inverse;
 
 private:	
-	mutable std::map<int, float*> _luts;
+	mutable std::map<int, double*> _luts;
 };
 
 }
diff --git a/src/xyz_frame.cc b/src/xyz_frame.cc
index 48098361..f1c69491 100644
--- a/src/xyz_frame.cc
+++ b/src/xyz_frame.cc
@@ -72,7 +72,7 @@ XYZFrame::~XYZFrame ()
 }
 
 /** @param c Component index (0, 1 or 2)
- *  @return Pointer to the data for component c.
+ *  @return Pointer to the data for component c; 12-bit values from 0-4095.
  */
 int *
 XYZFrame::data (int c) const