geom/m46148: neighbour pattern reduction from N10|7|5 to N9|5|3|2

This proposal reduces the number of neighbour configurations used
in occupancy contextualisation from {10, 10, 10, 10, 10, 10, 7, 5}
to {9, 9, 9, 9, 5, 5, 3, 2} by replacing the 64-to-10, 10-to-7,
and 10-to-5 mapping tables with 64-to-9, 9-to-5, and 9-to-3 tables.

tmc3/geometry_octree.h

@@ -137,7 +137,7 @@ inline NeighPattern64toX&
 neighPattern64toR1(const GeometryParameterSet& gps)
 {
   if (!gps.neighbour_context_restriction_flag)
-    return kNeighPattern64to10;
+    return kNeighPattern64to9;
   return kNeighPattern64to6;
 }
 
@@ -162,14 +162,14 @@ struct CtxModelOctreeOccupancy {
 class CtxMapOctreeOccupancy {
 public:
   struct CtxIdxMap {
-    uint8_t b0[10];
-    uint8_t b1[20];
-    uint8_t b2[39];
-    uint8_t b3[76];
-    uint8_t b4[149];
-    uint8_t b5[294];
-    uint8_t b6[391];
-    uint8_t b7[520];
+    uint8_t b0[9];
+    uint8_t b1[18];
+    uint8_t b2[35];
+    uint8_t b3[68];
+    uint8_t b4[69];
+    uint8_t b5[134];
+    uint8_t b6[135];
+    uint8_t b7[136];
   };
 
   CtxMapOctreeOccupancy();

tmc3/geometry_octree_decoder.cpp

@@ -62,7 +62,7 @@ public:
     int mappedOccAdjGt1);
 
   int decodeOccupancyNeighNZ(
-    int neighPattern10,
+    int neighPattern,
     int mappedOccIsPredicted,
     int mappedOccPrediction,
     int mappedOccAdjGt0,
@@ -205,14 +205,22 @@ GeometryOctreeDecoder::decodeOccupancyNeighZ(
 
 int
 GeometryOctreeDecoder::decodeOccupancyNeighNZ(
-  int neighPattern10,
+  int neighPattern,
   int mappedOccIsPredicted,
   int mappedOccPrediction,
   int mappedOccAdjGt0,
   int mappedOccAdjGt1)
 {
-  int neighPattern7 = kNeighPattern10to7[neighPattern10];
-  int neighPattern5 = kNeighPattern7to5[neighPattern7];
+  // code occupancy using the neighbour configuration context
+  // with reduction from 64 states to 9 (or 6).
+  int neighPatternR1 = _neighPattern64toR1[neighPattern];
+
+  //  int neighPattern9 = kNeighPattern64to9[neighPattern];
+  int neighPattern5 = kNeighPattern9to5[neighPatternR1];
+  int neighPattern3 = kNeighPattern9to3[neighPatternR1];
+
+  //  int neighPattern7 = kNeighPattern10to7[neighPattern10];
+  //  int neighPattern5 = kNeighPattern7to5[neighPattern7];
 
   int occupancy = 0;
   int partialOccupancy = 0;
@@ -221,17 +229,18 @@ GeometryOctreeDecoder::decodeOccupancyNeighNZ(
   // NB: offsets are added since ctxIdxMap is shared between Z and NZ cases.
   for (int i = 0; i < 8; i++) {
     int idx;
-    if (i < 6) {
-      idx = ((neighPattern10 - 1) << i) + partialOccupancy + i + 1;
+    if (i < 4) {
+      idx = ((neighPatternR1 - 1) << i) + partialOccupancy + i + 1;
+    } else if (i < 6) {
+      idx = ((neighPattern5 - 1) << i) + partialOccupancy + i + 1;
     } else if (i == 6) {
-      idx = ((neighPattern7 - 1) << i) + partialOccupancy + i + 1;
+      idx = ((neighPattern3 - 1) << i) + partialOccupancy + i + 1;
     } else if (i == 7) {
-      idx = ((neighPattern5 - 1) << i) + partialOccupancy + i + 1;
+      idx = partialOccupancy + i + 1;
     } else {
       // work around clang -Wsometimes-uninitialized fault
       break;
     }
-
     // NB: if firt 7 bits are 0, then the last is implicitly 1.
     int bit = 1;
     int bitIsPredicted = (mappedOccIsPredicted >> kOccBitCodingOrder[i]) & 1;
@@ -272,11 +281,8 @@ GeometryOctreeDecoder::decodeOccupancyBitwise(
       mappedOccAdjGt1);
   }
 
-  // code occupancy using the neighbour configuration context
-  // with reduction from 64 states to 10 (or 6).
-  int neighPatternR1 = _neighPattern64toR1[neighPattern];
   return decodeOccupancyNeighNZ(
-    neighPatternR1, mappedOccIsPredicted, mappedOccPrediction, mappedOccAdjGt0,
+    neighPattern, mappedOccIsPredicted, mappedOccPrediction, mappedOccAdjGt0,
     mappedOccAdjGt1);
 }
 

tmc3/geometry_octree_encoder.cpp

@@ -63,7 +63,7 @@ public:
     int mappedOccAdjGt1);
 
   void encodeOccupancyNeighNZ(
-    int neighPattern10,
+    int neighPattern,
     int mappedOccupancy,
     int mappedOccIsPredicted,
     int mappedOccPrediction,
@@ -208,27 +208,37 @@ GeometryOctreeEncoder::encodeOccupancyNeighZ(
 
 void
 GeometryOctreeEncoder::encodeOccupancyNeighNZ(
-  int neighPattern10,
+  int neighPattern,
   int mappedOccupancy,
   int mappedOccIsPredicted,
   int mappedOccPrediction,
   int mappedOccAdjGt0,
   int mappedOccAdjGt1)
 {
-  int neighPattern7 = kNeighPattern10to7[neighPattern10];
-  int neighPattern5 = kNeighPattern7to5[neighPattern7];
+  // code occupancy using the neighbour configuration context
+  // with reduction from 64 states to 9 (or 6).
+  int neighPatternR1 = _neighPattern64toR1[neighPattern];
+
+  //  int neighPattern9 = kNeighPattern64to9[neighPattern];
+  int neighPattern5 = kNeighPattern9to5[neighPatternR1];
+  int neighPattern3 = kNeighPattern9to3[neighPatternR1];
+
+  //  int neighPattern7 = kNeighPattern10to7[neighPattern10];
+  //  int neighPattern5 = kNeighPattern7to5[neighPattern7];
 
   uint32_t partialOccupancy = 0;
 
   // NB: it is impossible for pattern to be 0 (handled in Z case).
   for (int i = 0; i < 8; i++) {
     int idx;
-    if (i < 6) {
-      idx = ((neighPattern10 - 1) << i) + partialOccupancy + i + 1;
+    if (i < 4) {
+      idx = ((neighPatternR1 - 1) << i) + partialOccupancy + i + 1;
+    } else if (i < 6) {
+      idx = ((neighPattern5 - 1) << i) + partialOccupancy + i + 1;
     } else if (i == 6) {
-      idx = ((neighPattern7 - 1) << i) + partialOccupancy + i + 1;
+      idx = ((neighPattern3 - 1) << i) + partialOccupancy + i + 1;
     } else if (i == 7) {
-      idx = ((neighPattern5 - 1) << i) + partialOccupancy + i + 1;
+      idx = partialOccupancy + i + 1;
     } else {
       // work around clang -Wsometimes-uninitialized fault
       break;
@@ -272,11 +282,8 @@ GeometryOctreeEncoder::encodeOccupancyBitwise(
     return;
   }
 
-  // code occupancy using the neighbour configuration context
-  // with reduction from 64 states to 10 (or 6).
-  int neighPatternR1 = _neighPattern64toR1[neighPattern];
   encodeOccupancyNeighNZ(
-    neighPatternR1, mappedOccupancy, mappedOccIsPredicted, mappedOccPrediction,
+    neighPattern, mappedOccupancy, mappedOccIsPredicted, mappedOccPrediction,
     mappedOccAdjGt0, mappedOccAdjGt1);
 }
 

tmc3/tables.cpp

@@ -38,16 +38,20 @@
 // indicates impossible values in the following table
 static const int x = 0;
 
-const uint8_t pcc::kNeighPattern64to10[64] = {
-  0, 1, 1, 2, 1, 3, 3, 4, 1, 3, 3, 4, 2, 4, 4, 5, 1, 3, 3, 4, 3, 6,
-  6, 7, 3, 6, 6, 7, 4, 7, 7, 8, 1, 3, 3, 4, 3, 6, 6, 7, 3, 6, 6, 7,
-  4, 7, 7, 8, 2, 4, 4, 5, 4, 7, 7, 8, 4, 7, 7, 8, 5, 8, 8, 9};
+const uint8_t pcc::kNeighPattern64to9[64] = {
+  0, 1, 1, 1, 1, 2, 2, 3, 1, 2, 2, 3, 1, 3, 3, 4, 1, 2, 2, 3, 2, 5,
+  5, 6, 2, 5, 5, 6, 3, 6, 6, 7, 1, 2, 2, 3, 2, 5, 5, 6, 2, 5, 5, 6,
+  3, 6, 6, 7, 1, 3, 3, 4, 3, 6, 6, 7, 3, 6, 6, 7, 4, 7, 7, 8};
 
 const uint8_t pcc::kNeighPattern64to6[64] = {
   0, 4, 4, x, 4, 2, 2, x, 4, 2, 2, x, x, x, x, x, 5, 3, 3, x, 3, 1,
   1, x, 3, 1, 1, x, x, x, x, x, 5, 3, 3, x, 3, 1, 1, x, 3, 1, 1, x,
   x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x};
 
+const uint8_t pcc::kNeighPattern9to5[9] = {0, 1, 2, 3, 1, 2, 3, 4, 4};
+
+const uint8_t pcc::kNeighPattern9to3[9] = {0, 1, 1, 2, 2, 1, 2, 2, 2};
+
 const uint8_t pcc::kNeighPattern10to7[10] = {0, 1, 2, 3, 4, 5, 3, 4, 5, 6};
 
 const uint8_t pcc::kNeighPattern7to5[7] = {0, 1, 2, 1, 4, 4, 3};

tmc3/tables.h

@@ -40,8 +40,10 @@
 namespace pcc {
 
 // Symmetry reduction of 64 neighbour pattern to 10
-extern const uint8_t kNeighPattern64to10[64];
+extern const uint8_t kNeighPattern64to9[64];
 extern const uint8_t kNeighPattern64to6[64];
+extern const uint8_t kNeighPattern9to5[9];
+extern const uint8_t kNeighPattern9to3[9];
 extern const uint8_t kNeighPattern10to7[10];
 extern const uint8_t kNeighPattern7to5[7];