commit 34f2b74d530a99318df61e5011a555b0d750a768
author Rupert Swarbrick <rupert.swarbrick@argondesign.com> Mon Oct 30 11:52:13 2017 +0000
committer Debargha Mukherjee <debargha@google.com> Mon Oct 30 18:49:58 2017 +0000
tree 98f9e0a95aba4e78491639b87395177b89baf4e8
parent cf842ad2676c5a98fdc6b3adf1dfba282f35da56

Correct scaling in av1_loop_restoration_corners_in_sb

I'd got the scaling backwards. This gets it right and adds a comment
explaining the calculation.

Change-Id: Ife2913700cc73996c09b702b394832799c449a8c

av1/common/restoration.c

diff --git a/av1/common/restoration.c b/av1/common/restoration.c
index e93ca49..6e60ae4 100644
--- a/av1/common/restoration.c
+++ b/av1/common/restoration.c
@@ -1680,8 +1680,16 @@
   const int mi_rel_col1 = mi_rel_col0 + mi_size_wide[bsize];
 
 #if CONFIG_FRAME_SUPERRES
-  const int mi_to_num = MI_SIZE * SCALE_NUMERATOR;
-  const int denom = cm->superres_scale_denominator;
+  // Write m for the relative mi column or row, D for the superres denominator
+  // and N for the superres numerator. If u is the upscaled (called "unscaled"
+  // elsewhere) pixel offset then we can write the downscaled pixel offset in
+  // two ways as:
+  //
+  //   MI_SIZE * m = N / D u
+  //
+  // from which we get u = D * MI_SIZE * m / N
+  const int mi_to_num = MI_SIZE * cm->superres_scale_denominator;
+  const int denom = SCALE_NUMERATOR;
 #else
   const int mi_to_num = MI_SIZE;
   const int denom = 1;