HDR preparations

ui/gfx/color_transform.cc

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/color_transform.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 270 matching lines @@
       v = fmax(0.0f, v);
       float a = 1.055f;
       float b = 0.0031308f;
       if (v < b) {
         return 12.92f * v;
       } else {
         return a * powf(v, 1.0f / 2.4f) - (a - 1.0f);
       }
     }
     case ColorSpace::TransferID::SMPTEST2084: {
+      // Go from scRGB levels to 0-1.
+      v *= 80.0f / 10000.0f;
       v = fmax(0.0f, v);
       float m1 = (2610.0f / 4096.0f) / 4.0f;
       float m2 = (2523.0f / 4096.0f) * 128.0f;
       float c1 = 3424.0f / 4096.0f;
       float c2 = (2413.0f / 4096.0f) * 32.0f;
       float c3 = (2392.0f / 4096.0f) * 32.0f;
       return powf((c1 + c2 * powf(v, m1)) / (1.0f + c3 * powf(v, m1)), m2);
     }
 
     case ColorSpace::TransferID::SMPTEST428_1:
       v = fmax(0.0f, v);
       return powf(48.0f * v + 52.37f, 1.0f / 2.6f);
 
     // Spec: http://www.arib.or.jp/english/html/overview/doc/2-STD-B67v1_0.pdf
     case ColorSpace::TransferID::ARIB_STD_B67: {
       const float a = 0.17883277f;
       const float b = 0.28466892f;
       const float c = 0.55991073f;
-      const float Lmax = 12.0f;
-      v = Lmax * fmax(0.0f, v);
+      v = fmax(0.0f, v);
       if (v <= 1)
         return 0.5f * sqrtf(v);
       else
         return a * log(v - b) + c;
     }
 
     // Chrome-specific values below
     case ColorSpace::TransferID::GAMMA24:
       v = fmax(0.0f, v);
       return powf(v, 1.0f / 2.4f);
@@ skipping 95 matching lines @@
       }
     }
 
     case ColorSpace::TransferID::SMPTEST2084: {
       v = fmax(0.0f, v);
       float m1 = (2610.0f / 4096.0f) / 4.0f;
       float m2 = (2523.0f / 4096.0f) * 128.0f;
       float c1 = 3424.0f / 4096.0f;
       float c2 = (2413.0f / 4096.0f) * 32.0f;
       float c3 = (2392.0f / 4096.0f) * 32.0f;
-      return powf(
+      v = powf(
           fmax(powf(v, 1.0f / m2) - c1, 0) / (c2 - c3 * powf(v, 1.0f / m2)),
           1.0f / m1);
+      // This matches the scRGB definition that 1.0 means 80 nits.
+      // TODO(hubbe): It would be *nice* if 1.0 meant more than that, but
+      // that might be difficult to do right now.
+      v *= 10000.0f / 80.0f;
+      return v;
     }
 
     case ColorSpace::TransferID::SMPTEST428_1:
       return (powf(v, 2.6f) - 52.37f) / 48.0f;
 
     // Chrome-specific values below
     case ColorSpace::TransferID::GAMMA24:
       v = fmax(0.0f, v);
       return powf(v, 2.4f);
 
     case ColorSpace::TransferID::SMPTEST2084_NON_HDR:
       v = fmax(0.0f, v);
       return fmin(2.3f * pow(v, 2.8f), v / 5.0f + 0.8f);
 
     // Spec: http://www.arib.or.jp/english/html/overview/doc/2-STD-B67v1_0.pdf
     case ColorSpace::TransferID::ARIB_STD_B67: {
       v = fmax(0.0f, v);
       const float a = 0.17883277f;
       const float b = 0.28466892f;
       const float c = 0.55991073f;
-      const float Lmax = 12.0f;
       float v_ = 0.0f;
       if (v <= 0.5f) {
         v_ = (v * 2.0f) * (v * 2.0f);
       } else {
         v_ = exp((v - c) / a) + b;
       }
-      return v_ / Lmax;
+      return v_;
     }
   }
 
   v = fmax(0.0f, v);
   float a = 1.099296826809442f;
   float b = 0.018053968510807f;
   if (v < FromLinear(ColorSpace::TransferID::BT709, b)) {
     return v / 4.5f;
   } else {
     return powf((v + a - 1.0f) / a, 1.0f / 0.45f);
@@ skipping 585 matching lines @@
       to_profile ? ColorSpace::CreateXYZD50() : to, intent, &builder);
   if (to_profile) {
     builder.Append(std::unique_ptr<ColorTransformInternal>(
         new QCMSColorTransform(GetXYZD50Profile(), to_profile)));
   }
 
   return builder.GetTransform();
 }
 
 }  // namespace gfx