geom/m50927: slice-based geometry quantization

This extends the geometry based quantisation scheme to:
 - add a per-slice QP offset, and
 - permit uniform quantisation of the whole slice without
   requiring signalling of an additional node QP offset.

Per node QP offset signalling is disabled by setting
positionQuantisationOctreeDepth=-1

doc/README.options.md

@@ -222,13 +222,18 @@ position scaling due to `positionQuantizationScale`.
 
 ### `--positionBaseQp=INT-VALUE`
 The quantisation parameter used to quantise geometry positions.  The
-effective QP may be varied according to `positionQuantisationOctreeDepth`.
+effective QP may be varied according to `positionSliceQpOffset` and
+`positionQuantisationOctreeDepth`.
 A QP equal to 4 results in a scale factor of 1.
 
+### `--positionSliceQpOffset=INT-VALUE`
+A per-slice offset to be applied to `positionBaseQp`.
+
 ### `--positionQuantisationOctreeDepth=INT-VALUE`
 The depth in the octree at which per-node QP offsets are signalled.
 A non-normative encoder process determines the QP offset based upon
-the local density of the octree.
+the local density of the octree.  A value of -1 disables signalling
+of per-node QP offsets.
 
 ### `--bitwiseOccupancyCoding=0|1`
 In octree geometry coding, there are both byte-wise and bit-wise tools to

tmc3/TMC3.cpp

@@ -551,9 +551,13 @@ ParseParameters(int argc, char* argv[], Parameters& params)
     params.encoder.gps.geom_base_qp, 4,
     "Base QP used in position quantisation")
 
+  ("positionSliceQpOffset",
+    params.encoder.gbh.geom_slice_qp_offset, 0,
+    "Per-slice QP offset used in position quantisation")
+
   ("positionQuantisationOctreeDepth",
-    params.encoder.gbh.geom_octree_qp_offset_depth, 3,
-    "Octree depth used for signalling position QP offsets\n")
+    params.encoder.gbh.geom_octree_qp_offset_depth, -1,
+    "Octree depth used for signalling position QP offsets (-1 => disabled)")
 
   (po::Section("Attributes"))
 

tmc3/encoder.cpp

@@ -282,6 +282,10 @@ PCCTMC3Encoder3::fixupParameterSets(EncoderParams* params)
   params->gps.geom_box_log2_scale_present_flag = true;
   params->gps.gps_geom_box_log2_scale = 0;
 
+  // don't enable octree qp offset signalling if disabled
+  params->gbh.geom_octree_qp_offset_enabled_flag =
+    params->gbh.geom_octree_qp_offset_depth >= 0;
+
   // fixup attribute parameters
   for (auto it : params->attributeIdxMap) {
     auto& attr_sps = params->sps.attributeSets[it.second];
@@ -463,7 +467,9 @@ PCCTMC3Encoder3::encodeGeometryBrick(
   gbh.geom_box_log2_scale = 0;
   gbh.geom_max_node_size_log2 = nodeSizeLog2;
   gbh.geom_num_points = int(pointCloud.getPointCount());
-  gbh.geom_octree_qp_offset_enabled_flag = _gps->geom_scaling_enabled_flag;
+  gbh.geom_slice_qp_offset = params->gbh.geom_slice_qp_offset;
+  gbh.geom_octree_qp_offset_enabled_flag =
+    params->gbh.geom_octree_qp_offset_enabled_flag;
   gbh.geom_octree_qp_offset_depth = params->gbh.geom_octree_qp_offset_depth;
   write(*_sps, *_gps, gbh, buf);
 

tmc3/geometry_octree_decoder.cpp

@@ -472,9 +472,13 @@ decodeGeometryOctree(
     occupancyAtlas.clear();
   }
 
+  int sliceQp = gps.geom_base_qp + gbh.geom_slice_qp_offset;
   int numLvlsUntilQpOffset = -1;
+
   if (gbh.geom_octree_qp_offset_enabled_flag)
     numLvlsUntilQpOffset = gbh.geom_octree_qp_offset_depth;
+  else if (gps.geom_scaling_enabled_flag)
+    node00.qp = sliceQp;
 
   for (; !fifo.empty(); fifo.pop_front()) {
     if (fifo.begin() == fifoCurrLvlEnd) {
@@ -500,7 +504,7 @@ decodeGeometryOctree(
     PCCOctree3Node& node0 = fifo.front();
 
     if (numLvlsUntilQpOffset == 0) {
-      node0.qp = decoder.decodeQpOffset() + gps.geom_base_qp;
+      node0.qp = decoder.decodeQpOffset() + sliceQp;
       node0.pos_base = node0.pos;
       node0.pos_quant = {0, 0, 0};
     }

tmc3/geometry_octree_encoder.cpp

@@ -561,15 +561,20 @@ encodeGeometryOctree(
   }
   Vec3<uint32_t> occupancyAtlasOrigin(0xffffffff);
 
-  int numLvlsUntilQpOffset = -1;
-  if (gbh.geom_octree_qp_offset_enabled_flag)
-    numLvlsUntilQpOffset = gbh.geom_octree_qp_offset_depth;
+  int numLvlsUntilQuantization = -1;
+  if (gps.geom_scaling_enabled_flag) {
+    numLvlsUntilQuantization = 0;
+    if (gbh.geom_octree_qp_offset_enabled_flag)
+      numLvlsUntilQuantization = gbh.geom_octree_qp_offset_depth;
+  }
+
+  int sliceQp = gps.geom_base_qp + gbh.geom_slice_qp_offset;
 
   // applied to the root node, just set the node qp
-  if (numLvlsUntilQpOffset == 0)
-    node00.qp = gps.geom_base_qp;
+  if (numLvlsUntilQuantization == 0)
+    node00.qp = sliceQp;
 
-  if (gbh.geom_octree_qp_offset_enabled_flag)
+  if (gps.geom_scaling_enabled_flag)
     pointCloud.copyPositions();
 
   for (; !fifo.empty(); fifo.pop_front()) {
@@ -588,20 +593,21 @@ encodeGeometryOctree(
 
       // determing a per node QP at the appropriate level
       // NB: this has no effect here if geom_octree_qp_offset_depth=0
-      if (--numLvlsUntilQpOffset == 0)
+      if (--numLvlsUntilQuantization == 0)
         calculateNodeQps(gps.geom_base_qp, fifo.begin(), fifoCurrLvlEnd);
     }
 
     PCCOctree3Node& node0 = fifo.front();
 
     // encode delta qp for each octree block
-    if (numLvlsUntilQpOffset == 0)
-      encoder.encodeQpOffset(node0.qp - gps.geom_base_qp);
+    if (
+      numLvlsUntilQuantization == 0 && gbh.geom_octree_qp_offset_enabled_flag)
+      encoder.encodeQpOffset(node0.qp - sliceQp);
 
     int shiftBits = (node0.qp - 4) / 6;
     int effectiveNodeSizeLog2 = nodeSizeLog2 - shiftBits;
     int effectiveChildSizeLog2 = effectiveNodeSizeLog2 - 1;
-    if (numLvlsUntilQpOffset == 0) {
+    if (numLvlsUntilQuantization == 0) {
       geometryQuantization(pointCloud, node0, nodeSizeLog2);
       if (gps.geom_unique_points_flag)
         checkDuplicatePoints(pointCloud, node0, pointIdxToDmIdx);
@@ -784,7 +790,7 @@ encodeGeometryOctree(
 
   // inverse quantise the point cloud
   // NB: this is done here to handle the partial tree coding case
-  if (gbh.geom_octree_qp_offset_enabled_flag)
+  if (gps.geom_scaling_enabled_flag)
     for (int i = 0; i < pointCloud.getPointCount(); i++)
       pointCloud[i] = pointCloud.getPositionReconstructed(i);
 

tmc3/hls.h

@@ -288,6 +288,9 @@ struct GeometryBrickHeader {
   int geom_max_node_size_log2;
   int geom_num_points;
 
+  // qp offset for geometry scaling (if enabled)
+  int geom_slice_qp_offset;
+
   // enables signalling of qp offsets within the octree
   bool geom_octree_qp_offset_enabled_flag;
 

tmc3/io_hls.cpp

@@ -406,6 +406,7 @@ write(
   bs.writeUn(sps.log2_max_frame_idx, gbh.frame_idx);
 
   if (gps.geom_scaling_enabled_flag) {
+    bs.writeSe(gbh.geom_slice_qp_offset);
     bs.write(gbh.geom_octree_qp_offset_enabled_flag);
     if (gbh.geom_octree_qp_offset_enabled_flag) {
       bs.writeUe(gbh.geom_octree_qp_offset_depth);
@@ -450,6 +451,7 @@ parseGbh(
 
   gbh.geom_octree_qp_offset_enabled_flag = false;
   if (gps.geom_scaling_enabled_flag) {
+    bs.readSe(&gbh.geom_slice_qp_offset);
     bs.read(&gbh.geom_octree_qp_offset_enabled_flag);
     if (gbh.geom_octree_qp_offset_enabled_flag)
       bs.readUe(&gbh.geom_octree_qp_offset_depth);