Fix YUV444 lossless mode unit test

Properly scale the chroma component size per color plane.

Change-Id: Ibf192d0e99f2fc3611beb82a3a9951ad09b292d3

av1/common/onyxc_int.h

@@ -739,6 +739,23 @@ static INLINE int is_chroma_reference(const int mi_row, const int mi_col,
 
   return ref_pos;
 }
+
+static INLINE BLOCK_SIZE scale_chroma_bsize(const BLOCK_SIZE bsize,
+                                            const int subsampling_x,
+                                            const int subsampling_y) {
+  BLOCK_SIZE bs = bsize;
+
+  if (bs < BLOCK_8X8) {
+    if (subsampling_x == 1 && subsampling_y == 1)
+      bs = BLOCK_8X8;
+    else if (subsampling_x == 1)
+      bs = BLOCK_8X4;
+    else if (subsampling_y == 1)
+      bs = BLOCK_4X8;
+  }
+
+  return bs;
+}
 #endif
 
 #if CONFIG_EXT_PARTITION_TYPES

av1/encoder/encodemb.c

@@ -940,11 +940,14 @@ void av1_encode_sb(AV1_COMMON *cm, MACROBLOCK *x, BLOCK_SIZE bsize,
 
   for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
 #if CONFIG_CB4X4 && !CONFIG_CHROMA_2X2
-    if (!is_chroma_reference(mi_row, mi_col, bsize,
-                             xd->plane[plane].subsampling_x,
-                             xd->plane[plane].subsampling_y))
+    const int subsampling_x = xd->plane[plane].subsampling_x;
+    const int subsampling_y = xd->plane[plane].subsampling_y;
+
+    if (!is_chroma_reference(mi_row, mi_col, bsize, subsampling_x,
+                             subsampling_y))
       continue;
-    if (plane) bsize = AOMMAX(bsize, BLOCK_8X8);
+
+    bsize = scale_chroma_bsize(bsize, subsampling_x, subsampling_y);
 #else
     (void)mi_row;
     (void)mi_col;

av1/encoder/rdopt.c

@@ -3754,7 +3754,9 @@ static int super_block_uvrd(const AV1_COMP *const cpi, MACROBLOCK *x,
 
 #if CONFIG_CB4X4 && !CONFIG_CHROMA_2X2
   if (x->skip_chroma_rd) return is_cost_valid;
-  bsize = AOMMAX(BLOCK_8X8, bsize);
+
+  bsize = scale_chroma_bsize(bsize, xd->plane[1].subsampling_x,
+                             xd->plane[1].subsampling_y);
 #endif  // CONFIG_CB4X4 && !CONFIG_CHROMA_2X2
 
 #if !CONFIG_PVQ