Added linear weight function, which yields the best SNR in case of sh…

…ot noise. Edges are smoothly clipped, to account for readout and compression noise. See Grandos2010 for analysis. Note that triangular weight is rather suboptimal and should not be the default.
Beep6581 · Mar 21, 2021 · 4821fd4 · 4821fd4
1 parent 0d159a2
commit 4821fd4
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Showing 6 changed files with 53 additions and 8 deletions.
diff --git a/src/Common/CommonFunctions.cpp b/src/Common/CommonFunctions.cpp
@@ -460,6 +460,8 @@ QString getQString(libhdr::fusion::WeightFunctionType wf) {
             return QObject::tr("Gaussian");
         case WEIGHT_FLAT:
             return QObject::tr("Flat");
+        case WEIGHT_LINEAR:
+            return QObject::tr("Linear");
     }
 
     return QString();

diff --git a/src/HdrCreation/weights.cpp b/src/HdrCreation/weights.cpp
@@ -20,8 +20,8 @@ WeightFunctionType WeightFunction::fromString(const std::string &type) {
     typedef map<string, WeightFunctionType, pfs::utils::StringUnsensitiveComp>
         Dict;
     static Dict v = map_list_of("triangular", WEIGHT_TRIANGULAR)(
-        "gaussian", WEIGHT_GAUSSIAN)("plateau", WEIGHT_PLATEAU)("flat",
-                                                                WEIGHT_FLAT);
+        "gaussian", WEIGHT_GAUSSIAN)("plateau", WEIGHT_PLATEAU)(
+        "flat", WEIGHT_FLAT)("linear", WEIGHT_LINEAR);
 
     Dict::const_iterator it = v.find(type);
     if (it != v.end()) {
@@ -128,6 +128,38 @@ static float maxTrustedValueFlat() {
     return 1.f + std::numeric_limits<float>::epsilon();
 }
 
+namespace {
+static const float s_linearThreshold = 0.00025f;
+}
+
+static float getWeightLinear(float input) {
+    if ((input < s_linearThreshold) ||
+        (input > (1.f - s_linearThreshold))) {
+        return 0.f;
+    }
+    /* Clipping is such that weights rise quadratically on both edges
+       and the quadratic part reaches 1 at clipWidth away from edges. */
+    const float clipWidth = 0.07f;
+    float clipDark = 1.f - exp(-input / (clipWidth * clipWidth));
+    float clipBright = 1.f - exp(-pow((1.f - input) / clipWidth, 2));
+    return input * clipDark * clipBright;
+}
+
+static void fillWeightLinear(WeightFunction::WeightContainer &weight) {
+    size_t divider = (weight.size() - 1);
+    for (size_t i = 0; i < weight.size(); ++i) {
+        weight[i] = getWeightLinear((float)i / divider);
+    }
+}
+
+static float minTrustedValueLinear() {
+    return 0.f - std::numeric_limits<float>::epsilon();
+}
+static float maxTrustedValueLinear() {
+    return 1.f + std::numeric_limits<float>::epsilon();
+}
+
+
 void WeightFunction::setType(WeightFunctionType type) {
     typedef void (*WeightFunctionCalculator)(WeightContainer &);
     typedef float (*WeightTrustedValue)();
@@ -146,13 +178,16 @@ void WeightFunction::setType(WeightFunctionType type) {
     WeightFunctionFiller fillter_g = {&fillWeightGaussian,
                                       &minTrustedValueGaussian,
                                       &maxTrustedValueGaussian};
-    WeightFunctionFiller fillter_p = {
-        &fillWeightPlateau, &minTrustedValuePlateau, &maxTrustedValuePlateau};
+    WeightFunctionFiller fillter_p = {&fillWeightPlateau,
+                                      &minTrustedValuePlateau,
+                                      &maxTrustedValuePlateau};
     WeightFunctionFiller fillter_f = {&fillWeightFlat, &minTrustedValueFlat,
                                       &maxTrustedValueFlat};
+    WeightFunctionFiller fillter_l = {&fillWeightLinear, &minTrustedValueLinear,
+                                      &maxTrustedValueLinear};
     static WeightFunctionFunc funcs =
         map_list_of(WEIGHT_TRIANGULAR, fillter_t)(WEIGHT_GAUSSIAN, fillter_g)(
-            WEIGHT_PLATEAU, fillter_p)(WEIGHT_FLAT, fillter_f);
+            WEIGHT_PLATEAU, fillter_p)(WEIGHT_FLAT, fillter_f)(WEIGHT_LINEAR, fillter_l);
 
     WeightFunctionType type_ = WEIGHT_TRIANGULAR;
     WeightFunctionFiller func_ = {&fillWeightTriangular,

diff --git a/src/HdrCreation/weights.h b/src/HdrCreation/weights.h
@@ -34,7 +34,8 @@ enum WeightFunctionType {
     WEIGHT_TRIANGULAR = 0,
     WEIGHT_GAUSSIAN = 1,
     WEIGHT_PLATEAU = 2,
-    WEIGHT_FLAT = 3
+    WEIGHT_FLAT = 3,
+    WEIGHT_LINEAR = 4
 };
 
 class WeightFunction {

diff --git a/src/HdrWizard/HdrWizard.cpp b/src/HdrWizard/HdrWizard.cpp
@@ -70,7 +70,7 @@ static const FusionOperator models_in_gui[] = {DEBEVEC, ROBERTSON,
                                                ROBERTSON_AUTO};
 
 static const WeightFunctionType weights_in_gui[] = {
-    WEIGHT_TRIANGULAR, WEIGHT_GAUSSIAN, WEIGHT_PLATEAU, WEIGHT_FLAT};
+    WEIGHT_TRIANGULAR, WEIGHT_GAUSSIAN, WEIGHT_PLATEAU, WEIGHT_FLAT, WEIGHT_LINEAR};
 
 namespace {
 

diff --git a/src/HdrWizard/HdrWizard.ui b/src/HdrWizard/HdrWizard.ui
@@ -719,6 +719,11 @@ p, li { white-space: pre-wrap; }
                 <string>Flat</string>
                </property>
               </item>
+              <item>
+               <property name="text">
+                <string>Linear</string>
+               </property>
+              </item>
              </widget>
             </item>
             <item row="7" column="1" colspan="2">

diff --git a/src/MainCli/commandline.cpp b/src/MainCli/commandline.cpp
@@ -177,7 +177,7 @@ int CommandLineInterfaceManager::execCommandLineParams() {
             .constData());
     hdr_desc.add_options()(
         "hdrWeight", po::value<std::string>(),
-        tr("weight = triangular|gaussian|plateau|flat (Default is triangular)")
+        tr("weight = triangular|gaussian|plateau|flat|linear (Default is triangular)")
             .toUtf8()
             .constData())("hdrResponseCurve", po::value<std::string>(),
                           tr("response curve = from_file|linear|gamma|log|srgb "
@@ -550,6 +550,8 @@ reinhard02|\nreinhard05|mai|mantiuk06|mantiuk08|\nvanhateren|lischinski] (Defaul
                 hdrcreationconfig.weightFunction = WEIGHT_PLATEAU;
             else if (strcmp(value, "flat") == 0)
                 hdrcreationconfig.weightFunction = WEIGHT_FLAT;
+            else if (strcmp(value, "linear") == 0)
+                hdrcreationconfig.weightFunction = WEIGHT_LINEAR;
             else
                 printErrorAndExit(
                     tr("Error: Unknown weight function specified."));