color: Do not enforce T(0)=0 and T(1)=1 constraints in approxmation

ui/gfx/icc_profile.cc

 // Copyright 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/icc_profile.h"
 
 #include <list>
 
 #include "base/containers/mru_cache.h"
 #include "base/lazy_instance.h"
 #include "base/synchronization/lock.h"
 #include "third_party/skia/include/core/SkColorSpaceXform.h"
 #include "third_party/skia/include/core/SkICC.h"
 #include "ui/gfx/color_transform.h"
 #include "ui/gfx/skia_color_space_util.h"
 
 namespace gfx {
 
 const uint64_t ICCProfile::test_id_adobe_rgb_ = 1;
 const uint64_t ICCProfile::test_id_color_spin_ = 2;
 const uint64_t ICCProfile::test_id_generic_rgb_ = 3;
 const uint64_t ICCProfile::test_id_srgb_ = 4;
 const uint64_t ICCProfile::test_id_no_analytic_tr_fn_ = 5;
 const uint64_t ICCProfile::test_id_a2b_only_ = 6;
+const uint64_t ICCProfile::test_id_overshoot_ = 7;
 
 namespace {
 
 // Allow keeping around a maximum of 8 cached ICC profiles. Beware that
 // we will do a linear search thorugh currently-cached ICC profiles,
 // when creating a new ICC profile.
 const size_t kMaxCachedICCProfiles = 8;
 
 struct Cache {
   Cache() : id_to_icc_profile_mru(kMaxCachedICCProfiles) {}
@@ skipping 164 matching lines @@
       SkColorSpaceTransferFn fn;
       // First try to get a numerical transfer function from the profile.
       if (sk_icc->isNumericalTransferFn(&fn)) {
         parametric_color_space_is_accurate = true;
       } else {
         // If that fails, try to approximate the transfer function.
         float fn_max_error = 0;
         bool got_approximate_fn =
             SkApproximateTransferFn(sk_icc, &fn_max_error, &fn);
         if (got_approximate_fn) {
-          float kMaxError = 3.f / 256.f;
+          float kMaxError = 2.f / 256.f;
           if (fn_max_error < kMaxError) {
             parametric_color_space_is_accurate = true;
           } else {
             DLOG(ERROR) << "ICCProfile transfer function approximation "
                         << "inexact, error: " << 256.f * fn_max_error << "/256";
           }
         } else {
           // And if that fails, just say that the transfer function was sRGB.
           DLOG(ERROR) << "Failed to approximate ICCProfile transfer function.";
           gfx::ColorSpace::CreateSRGB().GetTransferFunction(&fn);
@@ skipping 30 matching lines @@
 
   // Add to the cache.
   {
     Cache& cache = g_cache.Get();
     base::AutoLock lock(cache.lock);
     cache.id_to_icc_profile_mru.Put(id_, *this);
   }
 }
 
 }  // namespace gfx