attr/m47399: slice level signalling of QP deltas

This commit permits signalling a per-slice delta QP for luma and
chroma attribute components.  The delta is relative to the base
value derived from the APS.

NB: while syntax support and derivation processes are provided,
this commit does not contain any method to control the delta
QP value at the encoder.

doc/README.options.md

@@ -275,3 +275,6 @@ Attribute's luma quantization parameter.
 ### `--qpChromaOffset=INT-VALUE`
 Attribute's chroma quantization quantization parameter relative to luma.
 Only applies when `attribute=colour`.
+
+### `--aps_slice_qp_deltas_present_flag=0|1`
+Enables signalling of per-slice QP values.

tmc3/AttributeDecoder.cpp

@@ -152,7 +152,7 @@ AttributeDecoder::decode(
 {
   int abhSize;
   AttributeBrickHeader abh = parseAbh(attr_aps, payload, &abhSize);
-  Quantizers qstep = deriveQuantSteps(attr_aps);
+  Quantizers qstep = deriveQuantSteps(attr_aps, abh);
 
   PCCResidualsDecoder decoder;
   decoder.start(payload.data() + abhSize, payload.size() - abhSize);

tmc3/AttributeEncoder.cpp

@@ -297,7 +297,7 @@ AttributeEncoder::encode(
   PCCPointSet3& pointCloud,
   PayloadBuffer* payload)
 {
-  Quantizers qstep = deriveQuantSteps(attr_aps);
+  Quantizers qstep = deriveQuantSteps(attr_aps, abh);
 
   PCCResidualsEncoder encoder;
   encoder.start(int(pointCloud.getPointCount()));

tmc3/TMC3.cpp

@@ -451,6 +451,10 @@ ParseParameters(int argc, char* argv[], Parameters& params)
   ("qpChromaOffset",
     params_attr.aps.aps_chroma_qp_offset, 0,
     "Attribute's chroma quantisation parameter offset (relative to luma)")
+
+  ("aps_slice_qp_deltas_present_flag",
+    params_attr.aps.aps_slice_qp_deltas_present_flag, false,
+    "Enable signalling of per-slice QP values")
   ;
   /* clang-format on */
 

tmc3/encoder.cpp

@@ -298,6 +298,8 @@ PCCTMC3Encoder3::compressPartition(
     abh.attr_attr_parameter_set_id = attr_aps.aps_attr_parameter_set_id;
     abh.attr_sps_attr_idx = attrIdx;
     abh.attr_geom_slice_id = _sliceId;
+    abh.attr_qp_delta_luma = 0;
+    abh.attr_qp_delta_chroma = 0;
     write(attr_aps, abh, &payload);
 
     AttributeEncoder attrEncoder;

tmc3/hls.h

@@ -245,6 +245,7 @@ struct AttributeParameterSet {
   // NB: these parameters are shared by all transform implementations
   int init_qp;
   int aps_chroma_qp_offset;
+  bool aps_slice_qp_deltas_present_flag;
 
   //--- raht parameters
   int raht_depth;
@@ -257,6 +258,8 @@ struct AttributeBrickHeader {
   int attr_sps_attr_idx;
   int attr_attr_parameter_set_id;
   int attr_geom_slice_id;
+  int attr_qp_delta_luma;
+  int attr_qp_delta_chroma;
 };
 
 //============================================================================

tmc3/io_hls.cpp

@@ -254,6 +254,7 @@ write(const AttributeParameterSet& aps)
   bs.writeUe(aps.init_qp);
   // todo(?): raht chroma qp support?
   bs.writeSe(aps.aps_chroma_qp_offset);
+  bs.write(aps.aps_slice_qp_deltas_present_flag);
 
   bool isLifting = aps.attr_encoding == AttributeEncoding::kLiftingTransform
     || aps.attr_encoding == AttributeEncoding::kPredictingTransform;
@@ -302,6 +303,7 @@ parseAps(const PayloadBuffer& buf)
   bs.readUe(&aps.init_qp);
   // todo(?): raht chroma qp support?
   bs.readSe(&aps.aps_chroma_qp_offset);
+  bs.read(&aps.aps_slice_qp_deltas_present_flag);
 
   bool isLifting = aps.attr_encoding == AttributeEncoding::kLiftingTransform
     || aps.attr_encoding == AttributeEncoding::kPredictingTransform;
@@ -421,6 +423,11 @@ write(
   bs.writeUe(abh.attr_sps_attr_idx);
   bs.writeUe(abh.attr_geom_slice_id);
 
+  if (aps.aps_slice_qp_deltas_present_flag) {
+    bs.writeSe(abh.attr_qp_delta_luma);
+    bs.writeSe(abh.attr_qp_delta_chroma);
+  }
+
   bs.byteAlign();
 }
 
@@ -457,6 +464,11 @@ parseAbh(
   bs.readUe(&abh.attr_sps_attr_idx);
   bs.readUe(&abh.attr_geom_slice_id);
 
+  if (aps.aps_slice_qp_deltas_present_flag) {
+    bs.readSe(&abh.attr_qp_delta_luma);
+    bs.readSe(&abh.attr_qp_delta_chroma);
+  }
+
   bs.byteAlign();
 
   if (bytesRead)

tmc3/quantization.cpp

@@ -43,11 +43,17 @@ namespace pcc {
 //============================================================================
 
 Quantizers
-deriveQuantSteps(const AttributeParameterSet& attr_aps)
+deriveQuantSteps(
+  const AttributeParameterSet& attr_aps, const AttributeBrickHeader& abh)
 {
   int sliceQpLuma = attr_aps.init_qp;
   int sliceQpChroma = attr_aps.init_qp + attr_aps.aps_chroma_qp_offset;
 
+  if (attr_aps.aps_slice_qp_deltas_present_flag) {
+    sliceQpLuma += abh.attr_qp_delta_luma;
+    sliceQpChroma += abh.attr_qp_delta_chroma;
+  }
+
   int qpShiftLuma = sliceQpLuma / 6;
   int qpShiftChroma = sliceQpChroma / 6;
 

tmc3/quantization.h

@@ -50,7 +50,8 @@ typedef std::array<int, 2> Quantizers;
 //============================================================================
 // Derive quantisation step sizes for each component given attribute
 
-Quantizers deriveQuantSteps(const AttributeParameterSet& attr_aps);
+Quantizers deriveQuantSteps(
+  const AttributeParameterSet& attr_aps, const AttributeBrickHeader& abh);
 
 //============================================================================