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chroma-encoder: Add NTSC wideband Y'UV encoding
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Adds the '--chroma-mode' option to select wideband-yuv or wideband-yiq
chroma encoding.  Y'IQ encoding is obsolete, so make Y'UV the default.
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@ifb @atsampson
ifb authored and atsampson committed Jun 8, 2022
1 parent 51a900d commit ff2bc55
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Showing 3 changed files with 60 additions and 19 deletions.
23 changes: 22 additions & 1 deletion tools/ld-chroma-decoder/encoder/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,12 @@ int main(int argc, char *argv[])
QCoreApplication::translate("main", "system"));
parser.addOption(systemOption);

// Option to select chroma mode (--chroma-mode)
QCommandLineOption chromaOption(QStringList() << "chroma-mode",
QCoreApplication::translate("main", "NTSC only. Chroma encoder mode to use (wideband-yuv, wideband-yiq; default: wideband-yuv)"),
QCoreApplication::translate("main", "chroma-mode"));
parser.addOption(chromaOption);

// -- Positional arguments --

// Positional argument to specify input video file
Expand Down Expand Up @@ -126,6 +132,21 @@ int main(int argc, char *argv[])
}
}

ChromaMode chromaMode = WIDEBAND_YUV;
QString chromaName;
if (parser.isSet(chromaOption)) {
chromaName = parser.value(chromaOption);
if (chromaName == "wideband-yiq") {
chromaMode = WIDEBAND_YIQ;
} else if (chromaName == "wideband-yuv") {
chromaMode = WIDEBAND_YUV;
} else {
// Quit with error
qCritical("Unsupported chroma encoder mode");
return -1;
}

}
// Open the input file
QFile rgbFile(inputFileName);
if (inputFileName == "-") {
Expand All @@ -150,7 +171,7 @@ int main(int argc, char *argv[])
// Encode the data
LdDecodeMetaData metaData;
if( system == NTSC ) {
NTSCEncoder encoder(rgbFile, tbcFile, metaData);
NTSCEncoder encoder(rgbFile, tbcFile, metaData, chromaMode);
if (!encoder.encode()) {
return -1;
}
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44 changes: 29 additions & 15 deletions tools/ld-chroma-decoder/encoder/ntscencoder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -50,8 +50,8 @@
#include <array>
#include <cmath>

NTSCEncoder::NTSCEncoder(QFile &_rgbFile, QFile &_tbcFile, LdDecodeMetaData &_metaData)
: rgbFile(_rgbFile), tbcFile(_tbcFile), metaData(_metaData)
NTSCEncoder::NTSCEncoder(QFile &_rgbFile, QFile &_tbcFile, LdDecodeMetaData &_metaData, ChromaMode &_chromaMode)
: rgbFile(_rgbFile), tbcFile(_tbcFile), metaData(_metaData), chromaMode(_chromaMode)
{
// NTSC subcarrier frequency [Poynton p511]
videoParameters.fSC = 315.0e6 / 88.0;
Expand Down Expand Up @@ -114,8 +114,8 @@ NTSCEncoder::NTSCEncoder(QFile &_rgbFile, QFile &_tbcFile, LdDecodeMetaData &_me

// Resize the output buffers.
Y.resize(videoParameters.fieldWidth);
I.resize(videoParameters.fieldWidth);
Q.resize(videoParameters.fieldWidth);
C1.resize(videoParameters.fieldWidth);
C2.resize(videoParameters.fieldWidth);
}

bool NTSCEncoder::encode()
Expand Down Expand Up @@ -369,27 +369,34 @@ void NTSCEncoder::encodeLine(qint32 fieldNo, qint32 frameLine, const quint16 *rg
burstAmplitude = 0.0;
}

// Clear Y'IQ buffers. Values in these are scaled so that 0.0 is black and
// Clear output buffers. Values in these are scaled so that 0.0 is black and
// 1.0 is white.
Y.fill(0.0);
I.fill(0.0);
Q.fill(0.0);
C1.fill(0.0);
C2.fill(0.0);

if (rgbData != nullptr) {
// Convert the R'G'B' data to Y'IQ form [Poynton p367 eq 30.2]
// Convert the R'G'B' data to component form
for (qint32 i = 0; i < activeWidth; i++) {
const double R = rgbData[i * 3] / 65535.0;
const double G = rgbData[(i * 3) + 1] / 65535.0;
const double B = rgbData[(i * 3) + 2] / 65535.0;
qint32 x = activeLeft + i;
Y[x] = (R * 0.299) + (G * 0.587) + (B * 0.114);
I[x] = (R * 0.595901) + (G * -0.274557) + (B * -0.321344);
Q[x] = (R * 0.211537) + (G * -0.522736) + (B * 0.311200);
if (chromaMode == WIDEBAND_YUV) {
// Y'UV [Poynton p337 eq 28.5]
C1[x] = (R * -0.147141) + (G * -0.288869) + (B * 0.436010);
C2[x] = (R * 0.614975) + (G * -0.514965) + (B * -0.100010);
} else {
// Y'IQ [Poynton p367 eq 30.2]
C1[x] = (R * 0.595901) + (G * -0.274557) + (B * -0.321344);
C2[x] = (R * 0.211537) + (G * -0.522736) + (B * 0.311200);
}
}

// Low-pass filter I and Q to 1.3 MHz [Poynton p342]
uvFilter.apply(I);
uvFilter.apply(Q);
// Low-pass filter chroma components to 1.3 MHz [Poynton p342]
uvFilter.apply(C1);
uvFilter.apply(C2);
}

for (qint32 x = 0; x < outputLine.size(); x++) {
Expand All @@ -400,8 +407,15 @@ void NTSCEncoder::encodeLine(qint32 fieldNo, qint32 frameLine, const quint16 *rg
// Generate colorburst
const double burst = sin(a + burstOffset) * burstAmplitude / 2.0;

// Encode the chroma signal [Poynton p368]
const double chroma = Q[x] * sin(a + 33.0) + I[x] * cos(a + 33.0);
// Encode the chroma signal
double chroma;
if (chromaMode == WIDEBAND_YUV) {
// Y'UV [Poynton p338]
chroma = C1[x] * sin(a - 33.0 - 123.0) + C2[x] * cos(a - 33.0 - 123.0);
} else {
// Y'IQ [Poynton p368]
chroma = C2[x] * sin(a + 33.0) + C1[x] * cos(a + 33.0);
}

// Combine everything to make up the composite signal
const double burstGate = raisedCosineGate(t, burstStartTime, burstEndTime, halfBurstRiseTime);
Expand Down
12 changes: 9 additions & 3 deletions tools/ld-chroma-decoder/encoder/ntscencoder.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,10 +32,15 @@

#include "lddecodemetadata.h"

enum ChromaMode {
WIDEBAND_YUV = 0, // Y'UV
WIDEBAND_YIQ, // Y'IQ
};

class NTSCEncoder
{
public:
NTSCEncoder(QFile &rgbFile, QFile &tbcFile, LdDecodeMetaData &metaData);
NTSCEncoder(QFile &rgbFile, QFile &tbcFile, LdDecodeMetaData &metaData, ChromaMode &chromaMode);

// Encode RGB stream to NTSC.
// Returns true on success; on failure, prints an error and returns false.
Expand All @@ -49,6 +54,7 @@ class NTSCEncoder
QFile &rgbFile;
QFile &tbcFile;
LdDecodeMetaData &metaData;
ChromaMode chromaMode;

LdDecodeMetaData::VideoParameters videoParameters;
qint32 activeWidth;
Expand All @@ -58,8 +64,8 @@ class NTSCEncoder

QByteArray rgbFrame;
QVector<double> Y;
QVector<double> I;
QVector<double> Q;
QVector<double> C1;
QVector<double> C2;
};

#endif

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