Roll skia/third_party/skcms 4028d14..8e64fbf (1 commits)

https://skia.googlesource.com/skcms.git/+log/4028d14..8e64fbf

2018-04-24 brianosman@google.com skcms_EnsureUsableAsDestinationWithSingleCurve


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TBR=stani@google.com

Change-Id: I4847f6687e95aca7e1b98b9bb24bcd12ed0fa2cd
Reviewed-on: https://skia-review.googlesource.com/123399
Reviewed-by: skcms-skia-autoroll <skcms-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/third_party/skcms/src/Transform.c b/third_party/skcms/src/Transform.c
index b3a6b55705..16cfaec0a2 100644
--- a/third_party/skcms/src/Transform.c
+++ b/third_party/skcms/src/Transform.c
@@ -6,6 +6,7 @@
  */
 
 #include "../skcms.h"
+#include "GaussNewton.h"
 #include "LinearAlgebra.h"
 #include "Macros.h"
 #include "PortableMath.h"
@@ -643,3 +644,46 @@ void skcms_EnsureUsableAsDestination(skcms_ICCProfile* profile, const skcms_ICCP
     *profile = ok;
     assert_usable_as_destination(profile);
 }
+
+static float max_roundtrip_error(const skcms_TransferFunction* inv_tf, const skcms_Curve* curve) {
+    int N = curve->table_entries ? (int)curve->table_entries : 256;
+    const float x_scale = 1.0f / (N - 1);
+    float err = 0;
+    for (int i = 0; i < N; i++) {
+        float x = i * x_scale,
+              y = skcms_eval_curve(x, curve);
+        err = fmaxf_(err, fabsf_(x - skcms_TransferFunction_eval(inv_tf, y)));
+    }
+    return err;
+}
+
+void skcms_EnsureUsableAsDestinationWithSingleCurve(skcms_ICCProfile* profile,
+                                                    const skcms_ICCProfile* fallback) {
+    // Operate on a copy of profile, so we can choose the best TF for the original curves
+    skcms_ICCProfile result = *profile;
+    skcms_EnsureUsableAsDestination(&result, fallback);
+
+    int best_tf = 0;
+    float min_max_error = INFINITY_;
+    const skcms_ICCProfile* ref = profile->has_trc ? profile : fallback;
+    for (int i = 0; i < 3; i++) {
+        skcms_TransferFunction inv;
+        skcms_TransferFunction_invert(&result.trc[i].parametric, &inv);
+
+        float err = 0;
+        for (int j = 0; j < 3; ++j) {
+            err = fmaxf_(err, max_roundtrip_error(&inv, &ref->trc[j]));
+        }
+        if (min_max_error > err) {
+            min_max_error = err;
+            best_tf = i;
+        }
+    }
+
+    for (int i = 0; i < 3; i++) {
+        result.trc[i].parametric = result.trc[best_tf].parametric;
+    }
+
+    *profile = result;
+    assert_usable_as_destination(profile);
+}