From 07a65fecbff0be2a1e89399ed38bb5cf46dac33b Mon Sep 17 00:00:00 2001
From: Allan Sandfeld Jensen <allan.jensen@qt.io>
Date: Thu, 25 Feb 2021 12:42:08 +0100
Subject: [PATCH] Fix logic problems with table based grayscale ICC profiles

White-point was calculated wrongly and some tables could cause bad
behavior in the tables.

Change-Id: I24e8f5f3cc1306f5f898a4acbf7b008e26bd04e2
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
(cherry picked from commit f493d41722fc76a04f699ea26128fdf3d215d913)
---
 src/gui/painting/qcolortransfertable_p.h | 8 ++++----
 src/gui/painting/qicc.cpp                | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/gui/painting/qcolortransfertable_p.h b/src/gui/painting/qcolortransfertable_p.h
index fdf68b78da6..2d8f41e0860 100644
--- a/src/gui/painting/qcolortransfertable_p.h
+++ b/src/gui/painting/qcolortransfertable_p.h
@@ -136,7 +136,7 @@ public:
             return 1.0f;
         if (!m_table16.isEmpty()) {
             float v = x * 65535.0f;
-            uint32_t i = std::floor(resultLargerThan * (m_tableSize - 1)) + 1;
+            uint32_t i = std::floor(resultLargerThan * (m_tableSize - 1));
             for ( ; i < m_tableSize; ++i) {
                 if (m_table16[i] > v)
                     break;
@@ -145,14 +145,14 @@ public:
                 return 1.0f;
             float y1 = m_table16[i - 1];
             float y2 = m_table16[i];
-            Q_ASSERT(x >= y1 && x < y2);
+            Q_ASSERT(v >= y1 && v <= y2);
             float fr = (v - y1) / (y2 - y1);
             return (i + fr) * (1.0f / (m_tableSize - 1));
 
         }
         if (!m_table8.isEmpty()) {
             float v = x * 255.0f;
-            uint32_t i = std::floor(resultLargerThan * (m_tableSize - 1)) + 1;
+            uint32_t i = std::floor(resultLargerThan * (m_tableSize - 1));
             for ( ; i < m_tableSize; ++i) {
                 if (m_table8[i] > v)
                     break;
@@ -161,7 +161,7 @@ public:
                 return 1.0f;
             float y1 = m_table8[i - 1];
             float y2 = m_table8[i];
-            Q_ASSERT(x >= y1 && x < y2);
+            Q_ASSERT(v >= y1 && v <= y2);
             float fr = (v - y1) / (y2 - y1);
             return (i + fr) * (1.0f / (m_tableSize - 1));
         }
diff --git a/src/gui/painting/qicc.cpp b/src/gui/painting/qicc.cpp
index 0acd458eff3..028e800c48e 100644
--- a/src/gui/painting/qicc.cpp
+++ b/src/gui/painting/qicc.cpp
@@ -759,7 +759,7 @@ bool fromIccProfile(const QByteArray &data, QColorSpace *colorSpace)
         } else {
             colorspaceDPtr->primaries = QColorSpace::Primaries::Custom;
             // Calculate chromaticity from xyz (assuming y == 1.0f).
-            float y = 1.0f / (1.0f + whitePoint.z - whitePoint.x);
+            float y = 1.0f / (1.0f + whitePoint.z + whitePoint.x);
             float x = whitePoint.x * y;
             QColorSpacePrimaries primaries(QColorSpace::Primaries::SRgb);
             primaries.whitePoint = QPointF(x,y);