NTSC filters: recreate and use more accurate values

src/Makefile.am

@@ -15,8 +15,8 @@ applentsc.cpp card.cpp cassette.cpp cassettein.cpp cassetteout.cpp \
 clipboardhandler.cpp clockcard.cpp \
 configep2.cpp cpu.cpp diskbytes.cpp diskcontroller.cpp drive.cpp drivemotor.cpp \
 emptyslot.cpp emulator.cpp firmwarecard.cpp gui.cpp hypermode.cpp \
-keyboard.cpp keyboardbuffermode.cpp languagecard.cpp lowpass_1_5_mhz.cpp \
-lowpass_3_58_mhz.cpp lss.cpp main.cpp memory.cpp paddlebuttonstates.cpp \
+keyboard.cpp keyboardbuffermode.cpp languagecard.cpp filterchroma.cpp \
+filterluma.cpp lss.cpp main.cpp memory.cpp paddlebuttonstates.cpp \
 paddles.cpp picturegenerator.cpp powerupreset.cpp raminitializer.cpp \
 screenimage.cpp slots.cpp speakerclicker.cpp standardin.cpp \
 standardinproducer.cpp standardout.cpp steppermotor.cpp textcharacters.cpp \
@@ -30,8 +30,8 @@ noinst_HEADERS = a2colorsobserved.h addressbus.h analogtv.h apple2.h applentsc.h
 card.h cassette.h cassettein.h cassetteout.h \
 clipboardhandler.h clockcard.h configep2.h cpu.h diskbytes.h \
 diskcontroller.h drive.h drivemotor.h e2const.h emptyslot.h emulator.h firmwarecard.h font3x5.h gui.h \
-hypermode.h keyboardbuffermode.h keyboard.h languagecard.h lowpass_1_5_mhz.h \
-lowpass_3_58_mhz.h lss.h memory.h paddlebuttonstates.h paddles.h picturegenerator.h \
+hypermode.h keyboardbuffermode.h keyboard.h languagecard.h filterchroma.h \
+filterluma.h lss.h memory.h paddlebuttonstates.h paddles.h picturegenerator.h \
 powerupreset.h raminitializer.h screenimage.h slots.h speakerclicker.h \
 standardin.h standardinproducer.h standardout.h steppermotor.h \
 textcharacterimages.h textcharacters.h timable.h util.h \

src/analogtv.cpp

@@ -29,8 +29,8 @@
 #include "analogtv.h"
 #include "screenimage.h"
 #include "applentsc.h"
-#include "lowpass_3_58_mhz.h"
-#include "lowpass_1_5_mhz.h"
+#include "filterluma.h"
+#include "filterchroma.h"
 
 #include <map>
 
@@ -494,7 +494,7 @@ CB AnalogTV::get_cb(int lineno)
 }
 
 
-std::map<CB,IQ> cacheCB;
+static std::map<CB,IQ> cacheCB;
 
 const double AnalogTV::IQ_OFFSET_DEGREES = 33;
 const double AnalogTV::IQ_OFFSET_RADIANS = AnalogTV::IQ_OFFSET_DEGREES * 3.1415927 / 180;
@@ -538,26 +538,21 @@ IQ AnalogTV::get_iq_factor(const CB& cb)
 
 const int AnalogTV::IQINTOFF(130);
 
-void AnalogTV::ntsc_to_yiq(const int isignal, const int siglen, const IQ& iq_factor, int yiq[])
-{
-	Lowpass_3_58_MHz filterY;
-	Lowpass_1_5_MHz filterI;
-	Lowpass_1_5_MHz filterQ;
-	for (int off = 0; off < siglen; ++off)
-	{
+void AnalogTV::ntsc_to_yiq(const int isignal, const int siglen, const IQ& iq_factor, int yiq[]) {
+    FilterLuma filterY;
+    FilterChroma filterI;
+    FilterChroma filterQ;
+    for (int off = 0; off < siglen; ++off) {
         const int sig = this->signal[isignal + off];
-		const int y = filterY.next(sig); // + 40; // to show blacker-than-black levels
+        const int y = filterY.next(sig);
         int i;
         int q;
-		if (y < -2)
-		{
+        if (y < -2) {
             i = 0;
             q = 0;
-		}
-		else
-		{
-			i = filterI.next((int)(sig * iq_factor.get(off & 3)));
-			q = filterQ.next((int)(sig * iq_factor.get((off + 3) & 3)));
+        } else {
+            i = filterI.next(sig * iq_factor.get(off & 3));
+            q = filterQ.next(sig * iq_factor.get((off + 3) & 3));
         }
 
         yiq[off] = (((q+IQINTOFF)&0xff) << 16) | (((i+IQINTOFF)&0xff) << 8) | ((y+IQINTOFF)&0xff);

src/filterchroma.cpp

@@ -15,37 +15,29 @@
     You should have received a copy of the GNU General Public License
     along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
-#ifndef LOWPASS_1_5_MHZ_H
-#define LOWPASS_1_5_MHZ_H
+#include "filterchroma.h"
 
 /*
     Generated by the utility at http://www-users.cs.york.ac.uk/~fisher/mkfilter
-	then hand modified by Chris Mosher.
+    3rd order low-pass Butterworth filter at 1500000 Hz.
+    (sample rate 14318182 Hz)
 */
-class Lowpass_1_5_MHz
-{
-public:
-	Lowpass_1_5_MHz()
-	{
-		x[0] = x[1] = x[2] = 0;
-		y[0] = y[1] = y[2] = y[3] = y[4] = 0;
-	}
-	~Lowpass_1_5_MHz() { }
+#define GAIN 4.910093226e+01
 
-	int x[3];
-	int y[5];
-
-	int next(const int v)
-	{
-		x[0] = x[1]; x[1] = x[2];
-		x[2] = v >> 3;
-
-		y[0] = y[1]; y[1] = y[2]; y[2] = y[3]; y[3] = y[4];
-		y[4] = x[0]+x[2]+(y[1]>>2)-y[2]+y[3]+(y[3]>>1);
-
-		return y[4];
+FilterChroma::FilterChroma() {
+    xv[0]=xv[1]=xv[2]=xv[3]=0;
+    yv[0]=yv[1]=yv[2]=yv[3]=0;
 }
 
-};
+FilterChroma::~FilterChroma() {
+}
 
-#endif
+float FilterChroma::next(const float v) {
+    xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3];
+    xv[3] = v / GAIN;
+    yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3];
+    yv[3] =   (xv[0] + xv[3]) + 3 * (xv[1] + xv[2])
+        + (  0.2608994296 * yv[0]) + ( -1.1262209208 * yv[1])
+        + (  1.7023917944 * yv[2]);
+    return yv[3];
+}

src/filterchroma.h

@@ -15,4 +15,18 @@
     You should have received a copy of the GNU General Public License
     along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
-#include "lowpass_3_58_mhz.h"
+#ifndef FILTERCHROMA
+#define FILTERCHROMA
+
+class FilterChroma {
+    private:
+        float xv[4];
+        float yv[4];
+
+    public:
+        FilterChroma();
+        ~FilterChroma();
+        float next(const float v);
+};
+
+#endif

src/filterluma.cpp

@@ -0,0 +1,44 @@
+/*
+    epple2
+    Copyright (C) 2008 by Christopher A. Mosher <cmosher01@gmail.com>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY, without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+#include "filterluma.h"
+
+/*
+    Generated by the utility at http://www-users.cs.york.ac.uk/~fisher/mkfilter
+    3rd order low-pass Butterworth filter at 4500000 Hz with extra zero at 3500000 Hz.
+    (sample rate 14318182 Hz)
+*/
+
+#define GAIN 6.715664173
+
+FilterLuma::FilterLuma() {
+    xv[0]=xv[1]=xv[2]=xv[3]=xv[4]=xv[5]=0;
+    yv[0]=yv[1]=yv[2]=yv[3]=0;
+}
+
+FilterLuma::~FilterLuma() {
+}
+
+float FilterLuma::next(const float v) {
+    xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; xv[3] = xv[4]; xv[4] = xv[5];
+    xv[5] = v / GAIN;
+    yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3];
+    yv[3] =   (xv[0] + xv[5]) +   2.9302009676 * (xv[1] + xv[4]) +   3.7906029028 * (xv[2] + xv[3])
+        + ( -0.0757751449 * yv[0]) + ( -0.4803383261 * yv[1])
+        + ( -0.7432283875 * yv[2]);
+    return yv[3];
+}

src/filterluma.h

@@ -15,4 +15,18 @@
     You should have received a copy of the GNU General Public License
     along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
-#include "lowpass_1_5_mhz.h"
+#ifndef FILTERLUMA
+#define FILTERLUMA
+
+class FilterLuma {
+    private:
+        float xv[6];
+        float yv[4];
+
+    public:
+        FilterLuma();
+        ~FilterLuma();
+        float next(const float v);
+};
+
+#endif

src/lowpass_3_58_mhz.h

@@ -1,50 +0,0 @@
-/*
-    epple2
-    Copyright (C) 2008 by Christopher A. Mosher <cmosher01@gmail.com>
-
-    This program is free software: you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY, without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program. If not, see <http://www.gnu.org/licenses/>.
-*/
-#ifndef LOWPASS_3_58_MHZ_H
-#define LOWPASS_3_58_MHZ_H
-
-/*
-	Generated by the utility at http://www-users.cs.york.ac.uk/~fisher/mkfilter
-	then hand modified by Chris Mosher.
-*/
-class Lowpass_3_58_MHz
-{
-	int x[5];
-	int y[5];
-
-public:
-	Lowpass_3_58_MHz()
-	{
-		x[0] = x[1] = x[2] = x[3] = x[4] = 0;
-		y[0] = y[1] = y[2] = y[3] = y[4] = 0;
-	}
-	~Lowpass_3_58_MHz() { }
-
-	int next(const int v)
-	{
-		x[0] = x[1]; x[1] = x[2]; x[2] = x[3]; x[3] = x[4];
-		x[4] = v/6;
-
-		y[0] = y[1]; y[1] = y[2]; y[2] = y[3]; y[3] = y[4];
-		y[4] = x[0]+x[4]+((x[1]+x[2]+x[3])<<1)-(y[3]>>2);
-
-		return y[4];
-	}
-};
-
-#endif