commit 88c57a25cf91b6a69848940a36d9303b929c8837
author Ram Mohan <ram.mohan@ittiam.com> Mon Jul 24 16:04:46 2023 +0530
committer Dichen Zhang <dichenzhang@google.com> Wed Aug 02 22:26:19 2023 +0000
tree 99efa1c0af349059926b1dffef9103ce53019f9e
parent c1d4244a623121acd75ac335a1be671199320f9a

ultrahdr: correct offset used during look ups

The offset that is used during look ups, has a bias. This is corrected.

Bug: 294199334
Test: ./libultrahdr_test

Change-Id: Ib8f5fbefd93a6d9afaa5db3f845746becd0fcce1

libs/ultrahdr/gainmapmath.cpp

diff --git a/libs/ultrahdr/gainmapmath.cpp b/libs/ultrahdr/gainmapmath.cpp
index e1c5085..ae9c4ca 100644
--- a/libs/ultrahdr/gainmapmath.cpp
+++ b/libs/ultrahdr/gainmapmath.cpp
@@ -168,7 +168,7 @@
 
 // See IEC 61966-2-1, Equations F.5 and F.6.
 float srgbInvOetfLUT(float e_gamma) {
-  uint32_t value = static_cast<uint32_t>(e_gamma * kSrgbInvOETFNumEntries);
+  uint32_t value = static_cast<uint32_t>(e_gamma * (kSrgbInvOETFNumEntries - 1) + 0.5);
   //TODO() : Remove once conversion modules have appropriate clamping in place
   value = CLIP3(value, 0, kSrgbInvOETFNumEntries - 1);
   return kSrgbInvOETF[value];
@@ -288,7 +288,7 @@
 }
 
 float hlgOetfLUT(float e) {
-  uint32_t value = static_cast<uint32_t>(e * kHlgOETFNumEntries);
+  uint32_t value = static_cast<uint32_t>(e * (kHlgOETFNumEntries - 1) + 0.5);
   //TODO() : Remove once conversion modules have appropriate clamping in place
   value = CLIP3(value, 0, kHlgOETFNumEntries - 1);
 
@@ -315,7 +315,7 @@
 }
 
 float hlgInvOetfLUT(float e_gamma) {
-  uint32_t value = static_cast<uint32_t>(e_gamma * kHlgInvOETFNumEntries);
+  uint32_t value = static_cast<uint32_t>(e_gamma * (kHlgInvOETFNumEntries - 1) + 0.5);
   //TODO() : Remove once conversion modules have appropriate clamping in place
   value = CLIP3(value, 0, kHlgInvOETFNumEntries - 1);
 
@@ -344,7 +344,7 @@
 }
 
 float pqOetfLUT(float e) {
-  uint32_t value = static_cast<uint32_t>(e * kPqOETFNumEntries);
+  uint32_t value = static_cast<uint32_t>(e * (kPqOETFNumEntries - 1) + 0.5);
   //TODO() : Remove once conversion modules have appropriate clamping in place
   value = CLIP3(value, 0, kPqOETFNumEntries - 1);
 
@@ -376,7 +376,7 @@
 }
 
 float pqInvOetfLUT(float e_gamma) {
-  uint32_t value = static_cast<uint32_t>(e_gamma * kPqInvOETFNumEntries);
+  uint32_t value = static_cast<uint32_t>(e_gamma * (kPqInvOETFNumEntries - 1) + 0.5);
   //TODO() : Remove once conversion modules have appropriate clamping in place
   value = CLIP3(value, 0, kPqInvOETFNumEntries - 1);
 

libs/ultrahdr/include/ultrahdr/gainmapmath.h

diff --git a/libs/ultrahdr/include/ultrahdr/gainmapmath.h b/libs/ultrahdr/include/ultrahdr/gainmapmath.h
index 50b4d2f..9f1238f 100644
--- a/libs/ultrahdr/include/ultrahdr/gainmapmath.h
+++ b/libs/ultrahdr/include/ultrahdr/gainmapmath.h
@@ -172,7 +172,7 @@
   }
 
   float getGainFactor(float gain) {
-    uint32_t idx = static_cast<uint32_t>(gain * (kGainFactorNumEntries - 1));
+    uint32_t idx = static_cast<uint32_t>(gain * (kGainFactorNumEntries - 1) + 0.5);
     //TODO() : Remove once conversion modules have appropriate clamping in place
     idx = CLIP3(idx, 0, kGainFactorNumEntries - 1);
     return mGainTable[idx];