commit f6eaa159d74fc95b8cb28d7afa37ce0cb03aa9d3
author David Michael Barr <b@rr-dav.id.au> Wed Jul 19 19:42:28 2017 +0900
committer David Michael Barr <b@rr-dav.id.au> Sat Jul 29 00:44:42 2017 +0000
tree 9a18fbfb9b2a554f3f4d9df45d6b52de01b12781
parent 9136ab7ded3b404c64288da89152ecbe609be6b9

[CFL] Uniform Q3 alpha grid with extent [-2, 2]

Expand the range of alpha to [-2, 2] in Q3.
Jointly signal the signs, including zeros.
Use the signs to give context for each quadrant
and half-axis. The (0, 0) point is excluded.
Symmetry in alpha_u == alpha_v yields 6 contexts.

Results on Subset1 (Compared to 9136ab7d with CFL enabled)

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0792 | -0.7535 | -0.7574 |  -0.0639 | -0.0843 | -0.0665 |    -0.3324

Change-Id: I250369692e92a91d9c8d174a203d441217d15063
Signed-off-by: David Michael Barr <b@rr-dav.id.au>

av1/common/cfl.c

diff --git a/av1/common/cfl.c b/av1/common/cfl.c
index 7c88dd0..aff6b7d 100644
--- a/av1/common/cfl.c
+++ b/av1/common/cfl.c
@@ -227,17 +227,14 @@
   assert(a <= MAX_NUM_TXB);
 }
 
-static INLINE int cfl_idx_to_alpha(int alpha_idx, CFL_SIGN_TYPE alpha_sign,
+static INLINE int cfl_idx_to_alpha(int alpha_idx, int joint_sign,
                                    CFL_PRED_TYPE pred_type) {
-  const int mag_idx = cfl_alpha_codes[alpha_idx][pred_type];
-  const int abs_alpha_q3 = cfl_alpha_mags_q3[mag_idx];
-  if (alpha_sign == CFL_SIGN_POS) {
-    return abs_alpha_q3;
-  } else {
-    assert(abs_alpha_q3 != 0);
-    assert(cfl_alpha_mags_q3[mag_idx + 1] == -abs_alpha_q3);
-    return -abs_alpha_q3;
-  }
+  const int alpha_sign = (pred_type == CFL_PRED_U) ? CFL_SIGN_U(joint_sign)
+                                                   : CFL_SIGN_V(joint_sign);
+  if (alpha_sign == CFL_SIGN_ZERO) return 0;
+  const int abs_alpha_q3 =
+      (pred_type == CFL_PRED_U) ? CFL_IDX_U(alpha_idx) : CFL_IDX_V(alpha_idx);
+  return (alpha_sign == CFL_SIGN_POS) ? abs_alpha_q3 + 1 : -abs_alpha_q3 - 1;
 }
 
 // Predict the current transform block using CfL.
@@ -255,8 +252,8 @@
   const uint8_t *y_pix = cfl->y_down_pix;
 
   const int dc_pred = cfl->dc_pred[plane - 1];
-  const int alpha_q3 = cfl_idx_to_alpha(
-      mbmi->cfl_alpha_idx, mbmi->cfl_alpha_signs[plane - 1], plane - 1);
+  const int alpha_q3 =
+      cfl_idx_to_alpha(mbmi->cfl_alpha_idx, mbmi->cfl_alpha_signs, plane - 1);
 
   const int avg_row =
       (row << tx_size_wide_log2[0]) >> tx_size_wide_log2[tx_size];