Add chroma phase control.

To be precise, this is a rotation applied to the I/Q or U/V components
after filtering and demodulation but (for PAL) before the V-switch.

For NTSC it acts as a hue control. For PAL, it can be adjusted to
minimise Hanover bars when using the Simple PAL decoder.

The full adjustment range (-180 to +180 degrees) is allowed, but since
the adjustment will generally be small in practice, the slider in
ld-analyse uses a non-linear scale.

tools/ld-analyse/chromadecoderconfigdialog.cpp

@@ -26,6 +26,36 @@
 #include "chromadecoderconfigdialog.h"
 #include "ui_chromadecoderconfigdialog.h"
 
+#include <cmath>
+
+/*
+ * These two functions provide a non-linear mapping for sliders that control
+ * phase adjustments in degrees. The maximum range is from -180 to +180
+ * degrees, but phase errors are usually < 10 degrees so we need more precise
+ * adjustment in the middle.
+ */
+
+static constexpr double DEGREE_SLIDER_POWER = 3.0;
+static constexpr qint32 DEGREE_SLIDER_SCALE = 1000;
+
+static double degreesToSliderPos(double degrees) {
+    double sliderPos = pow(abs(degrees) / 180, 1 / DEGREE_SLIDER_POWER) * DEGREE_SLIDER_SCALE;
+    if (degrees < 0) {
+        return -sliderPos;
+    } else {
+        return sliderPos;
+    }
+}
+
+static double sliderPosToDegrees(double sliderPos) {
+    double degrees = pow(abs(sliderPos) / DEGREE_SLIDER_SCALE, DEGREE_SLIDER_POWER) * 180;
+    if (sliderPos < 0) {
+        return -degrees;
+    } else {
+        return degrees;
+    }
+}
+
 ChromaDecoderConfigDialog::ChromaDecoderConfigDialog(QWidget *parent) :
     QDialog(parent),
     ui(new Ui::ChromaDecoderConfigDialog)
@@ -36,6 +66,9 @@ ChromaDecoderConfigDialog::ChromaDecoderConfigDialog(QWidget *parent) :
     ui->chromaGainHorizontalSlider->setMinimum(0);
     ui->chromaGainHorizontalSlider->setMaximum(200);
 
+    ui->chromaPhaseHorizontalSlider->setMinimum(-DEGREE_SLIDER_SCALE);
+    ui->chromaPhaseHorizontalSlider->setMaximum(DEGREE_SLIDER_SCALE);
+
     ui->thresholdHorizontalSlider->setMinimum(0);
     ui->thresholdHorizontalSlider->setMaximum(100);
 
@@ -65,13 +98,15 @@ void ChromaDecoderConfigDialog::setConfiguration(bool _isSourcePal, const PalCol
     outputConfiguration = _outputConfiguration;
 
     palConfiguration.chromaGain = qBound(0.0, palConfiguration.chromaGain, 2.0);
+    palConfiguration.chromaPhase = qBound(-180.0, palConfiguration.chromaPhase, 180.0);
     palConfiguration.transformThreshold = qBound(0.0, palConfiguration.transformThreshold, 1.0);
     palConfiguration.yNRLevel = qBound(0.0, yNRLevel, 10.0);
     ntscConfiguration.cNRLevel = qBound(0.0, ntscConfiguration.cNRLevel, 10.0);
     ntscConfiguration.yNRLevel = qBound(0.0, yNRLevel, 10.0);
 
     // For settings that both decoders share, the PAL default takes precedence
     ntscConfiguration.chromaGain = palConfiguration.chromaGain;
+    ntscConfiguration.chromaPhase = palConfiguration.chromaPhase;
 
     // Select the tab corresponding to the current standard automatically
     if (isSourcePal) {
@@ -108,6 +143,12 @@ void ChromaDecoderConfigDialog::updateDialog()
 
     ui->chromaGainValueLabel->setEnabled(true);
     ui->chromaGainValueLabel->setText(QString::number(palConfiguration.chromaGain, 'f', 2));
+
+    ui->chromaPhaseHorizontalSlider->setEnabled(true);
+    ui->chromaPhaseHorizontalSlider->setValue(static_cast<qint32>(degreesToSliderPos(palConfiguration.chromaPhase)));
+
+    ui->chromaPhaseValueLabel->setEnabled(true);
+    ui->chromaPhaseValueLabel->setText(QString::number(palConfiguration.chromaPhase, 'f', 1) + QChar(0xB0));
 
     double yNRLevel = isSourcePal ? palConfiguration.yNRLevel : ntscConfiguration.yNRLevel;
 
@@ -205,6 +246,14 @@ void ChromaDecoderConfigDialog::on_chromaGainHorizontalSlider_valueChanged(int v
     emit chromaDecoderConfigChanged();
 }
 
+void ChromaDecoderConfigDialog::on_chromaPhaseHorizontalSlider_valueChanged(int value)
+{
+    palConfiguration.chromaPhase = sliderPosToDegrees(static_cast<double>(value));
+    ntscConfiguration.chromaPhase = palConfiguration.chromaPhase;
+    ui->chromaPhaseValueLabel->setText(QString::number(palConfiguration.chromaPhase, 'f', 1) + QChar(0xB0));
+    emit chromaDecoderConfigChanged();
+}
+
 void ChromaDecoderConfigDialog::on_palFilterButtonGroup_buttonClicked(QAbstractButton *button)
 {
     if (button == ui->palFilterPalColourRadioButton) {

tools/ld-analyse/chromadecoderconfigdialog.h

@@ -56,6 +56,7 @@ class ChromaDecoderConfigDialog : public QDialog
 
 private slots:
     void on_chromaGainHorizontalSlider_valueChanged(int value);
+    void on_chromaPhaseHorizontalSlider_valueChanged(int value);
 
     void on_palFilterButtonGroup_buttonClicked(QAbstractButton *button);
     void on_thresholdModeCheckBox_clicked();

tools/ld-analyse/chromadecoderconfigdialog.ui

@@ -41,6 +41,33 @@
      </property>
     </widget>
    </item>
+   <item>
+    <widget class="QLabel" name="chromaPhaseLabel">
+     <property name="text">
+      <string>Chroma phase:</string>
+     </property>
+    </widget>
+   </item>
+   <item>
+    <widget class="QSlider" name="chromaPhaseHorizontalSlider">
+     <property name="maximum">
+      <number>200</number>
+     </property>
+     <property name="orientation">
+      <enum>Qt::Horizontal</enum>
+     </property>
+    </widget>
+   </item>
+   <item>
+    <widget class="QLabel" name="chromaPhaseValueLabel">
+     <property name="text">
+      <string>0.0°</string>
+     </property>
+     <property name="alignment">
+      <set>Qt::AlignCenter</set>
+     </property>
+    </widget>
+   </item>
    <item>
     <widget class="QLabel" name="yNRLabel">
      <property name="text">

tools/ld-chroma-decoder/comb.cpp

@@ -181,7 +181,7 @@ void Comb::decodeFrames(const QVector<SourceField> &inputFields, qint32 startInd
         currentFrameBuffer->doYNR();
 
         // Transform I/Q to U/V
-        currentFrameBuffer->transformIQ(configuration.chromaGain);
+        currentFrameBuffer->transformIQ(configuration.chromaGain, configuration.chromaPhase);
 
         // Overlay the map if required
         if (configuration.dimensions == 3 && configuration.showMap) {
@@ -710,11 +710,12 @@ void Comb::FrameBuffer::doYNR()
 }
 
 // Transform I/Q into U/V, and apply chroma gain
-void Comb::FrameBuffer::transformIQ(double chromaGain)
+void Comb::FrameBuffer::transformIQ(double chromaGain, double chromaPhase)
 {
     // Compute components for the rotation vector
-    const double bp = sin((33 * M_PI) / 180) * chromaGain;
-    const double bq = cos((33 * M_PI) / 180) * chromaGain;
+    const double theta = ((33 + chromaPhase) * M_PI) / 180;
+    const double bp = sin(theta) * chromaGain;
+    const double bq = cos(theta) * chromaGain;
 
     // Apply the vector to all the samples
     for (qint32 lineNumber = videoParameters.firstActiveFrameLine; lineNumber < videoParameters.lastActiveFrameLine; lineNumber++) {

tools/ld-chroma-decoder/comb.h

@@ -5,7 +5,7 @@
     ld-chroma-decoder - Colourisation filter for ld-decode
     Copyright (C) 2018 Chad Page
     Copyright (C) 2018-2019 Simon Inns
-    Copyright (C) 2020 Adam Sampson
+    Copyright (C) 2020-2021 Adam Sampson
     Copyright (C) 2021 Phillip Blucas
 
     This file is part of ld-decode-tools.
@@ -47,6 +47,7 @@ class Comb
     // Comb filter configuration parameters
     struct Configuration {
         double chromaGain = 1.0;
+        double chromaPhase = 0.0;
         bool colorlpf = false;
         bool colorlpf_hq = true;
         qint32 dimensions = 2;
@@ -100,7 +101,7 @@ class Comb
         void adjustY();
         void doCNR();
         void doYNR();
-        void transformIQ(double chromaGain);
+        void transformIQ(double chromaGain, double chromaPhase);
 
         void overlayMap(const FrameBuffer &previousFrame, const FrameBuffer &nextFrame);
 

tools/ld-chroma-decoder/main.cpp

@@ -157,6 +157,12 @@ int main(int argc, char *argv[])
                                         QCoreApplication::translate("main", "number"));
     parser.addOption(chromaGainOption);
 
+    // Option to specify chroma phase
+    QCommandLineOption chromaPhaseOption(QStringList() << "chroma-phase",
+                                        QCoreApplication::translate("main", "Phase rotation applied to chroma components (degrees; default 0.0)"),
+                                        QCoreApplication::translate("main", "number"));
+    parser.addOption(chromaPhaseOption);
+
     // Option to select the output format (-p)
     QCommandLineOption outputFormatOption(QStringList() << "p" << "output-format",
                                        QCoreApplication::translate("main", "Output format (rgb, yuv, y4m; default rgb); RGB48, YUV444P16, GRAY16 pixel formats are supported"),
@@ -324,6 +330,12 @@ int main(int argc, char *argv[])
         }
     }
 
+    if (parser.isSet(chromaPhaseOption)) {
+        const double value = parser.value(chromaPhaseOption).toDouble();
+        palConfig.chromaPhase = value;
+        combConfig.chromaPhase = value;
+    }
+
     bool bwMode = parser.isSet(setBwModeOption);
     if (bwMode) {
         palConfig.chromaGain = 0.0;

tools/ld-chroma-decoder/palcolour.cpp

@@ -286,9 +286,11 @@ void PalColour::decodeField(const SourceField &inputField, const double *chromaD
         // Detect the colourburst from the composite signal
         detectBurst(line, compPtr);
 
-        // Scale line.bp/line.bq to apply gain adjustment
-        line.bp *= configuration.chromaGain;
-        line.bq *= configuration.chromaGain;
+        // Rotate and scale line.bp/line.bq to apply gain and phase adjustment
+        const double oldBp = line.bp, oldBq = line.bq;
+        const double theta = (configuration.chromaPhase * M_PI) / 180;
+        line.bp = (oldBp * cos(theta) - oldBq * sin(theta)) * configuration.chromaGain;
+        line.bq = (oldBp * sin(theta) + oldBq * cos(theta)) * configuration.chromaGain;
 
         if (configuration.chromaFilter == palColourFilter) {
             // Decode chroma and luma from the composite signal

tools/ld-chroma-decoder/palcolour.h

@@ -56,6 +56,7 @@ class PalColour
 
     struct Configuration {
         double chromaGain = 1.0;
+        double chromaPhase = 0.0;
         double yNRLevel = 0.5;
         bool simplePAL = false;
         ChromaFilterMode chromaFilter = palColourFilter;