Fix logic problems with table based grayscale ICC profiles

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

Pick-to: 6.1 6.0 5.15
Change-Id: I24e8f5f3cc1306f5f898a4acbf7b008e26bd04e2
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

2 files changed, 6 insertions, 6 deletions

diff --git a/src/gui/painting/qcolortransfertable_p.h b/src/gui/painting/qcolortransfertable_p.h
index 2812ed5685..bbc9f08dcc 100644
--- a/src/gui/painting/qcolortransfertable_p.h
+++ b/src/gui/painting/qcolortransfertable_p.h
@@ -119,7 +119,7 @@ public:
         x = std::clamp(x, 0.0f, 1.0f);
         x *= m_tableSize - 1;
         const uint32_t lo = static_cast<uint32_t>(std::floor(x));
-        const uint32_t hi = std::min(lo + 1, m_tableSize);
+        const uint32_t hi = std::min(lo + 1, m_tableSize - 1);
         const float frac = x - lo;
         if (!m_table16.isEmpty())
             return (m_table16[lo] * (1.0f - frac) + m_table16[hi] * frac) * (1.0f/65535.0f);
@@ -138,28 +138,28 @@ public:
             return 1.0f;
         if (!m_table16.isEmpty()) {
             const float v = x * 65535.0f;
-            uint32_t i = static_cast<uint32_t>(std::floor(resultLargerThan * (m_tableSize - 1))) + 1;
+            uint32_t i = static_cast<uint32_t>(std::floor(resultLargerThan * (m_tableSize - 1)));
             auto it = std::lower_bound(m_table16.cbegin() + i, m_table16.cend(), v);
             i = it - m_table16.cbegin();
             if (i >= m_tableSize - 1)
                 return 1.0f;
             const float y1 = m_table16[i - 1];
             const float y2 = m_table16[i];
-            Q_ASSERT(x >= y1 && x < y2);
+            Q_ASSERT(v >= y1 && v <= y2);
             const float fr = (v - y1) / (y2 - y1);
             return (i + fr) * (1.0f / (m_tableSize - 1));
 
         }
         if (!m_table8.isEmpty()) {
             const float v = x * 255.0f;
-            uint32_t i = static_cast<uint32_t>(std::floor(resultLargerThan * (m_tableSize - 1))) + 1;
+            uint32_t i = static_cast<uint32_t>(std::floor(resultLargerThan * (m_tableSize - 1)));
             auto it = std::lower_bound(m_table8.cbegin() + i, m_table8.cend(), v);
             i = it - m_table8.cbegin();
             if (i >= m_tableSize - 1)
                 return 1.0f;
             const float y1 = m_table8[i - 1];
             const float y2 = m_table8[i];
-            Q_ASSERT(x >= y1 && x < y2);
+            Q_ASSERT(v >= y1 && v <= y2);
             const 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 bacf76997f..25389121f3 100644
--- a/src/gui/painting/qicc.cpp
+++ b/src/gui/painting/qicc.cpp
@@ -757,7 +757,7 @@ 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);