From c93dfd7db7f7283b1f651bc65616f7f226686740 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 17 Jan 2026 22:50:35 -0500
Subject: [PATCH] Experiment with but discover that 'real' FIRs remain out of
 reach.

---
 Components/9918/Implementation/Fetch.hpp      |  3 +-
 .../ScanTarget/Shaders/ComputeKernels.metal   |  2 +-
 Outputs/ScanTargets/FilterGenerator.cpp       | 65 +++++++++++--------
 3 files changed, 40 insertions(+), 30 deletions(-)

diff --git a/Components/9918/Implementation/Fetch.hpp b/Components/9918/Implementation/Fetch.hpp
index 9a9062c66..652afa84f 100644
--- a/Components/9918/Implementation/Fetch.hpp
+++ b/Components/9918/Implementation/Fetch.hpp
@@ -286,7 +286,8 @@ private:
 
 		const AddressT graphic_location = base->sprite_generator_table_address_ & bits<11>(AddressT((name << 3) | sprite.row));
 		sprite.image[0] = base->ram_[graphic_location];
-		sprite.image[1] = base->ram_[graphic_location+16];
+		sprite.image[1] = base->ram_[graphic_location+16];	// TODO: occasional out-of-bounds accesses here. Check
+															// uninitialised Master System.
 
 		if constexpr (SpriteBuffer::test_is_filling) {
 			if(slot == ((mode == SpriteMode::Mode2) ? 7 : 3)) {
diff --git a/OSBindings/Mac/Clock Signal/ScanTarget/Shaders/ComputeKernels.metal b/OSBindings/Mac/Clock Signal/ScanTarget/Shaders/ComputeKernels.metal
index 2b43aa9b9..89e74199c 100644
--- a/OSBindings/Mac/Clock Signal/ScanTarget/Shaders/ComputeKernels.metal	
+++ b/OSBindings/Mac/Clock Signal/ScanTarget/Shaders/ComputeKernels.metal	
@@ -173,7 +173,7 @@ kernel void separateLumaKernel15(
 
 	return setSeparatedLumaChroma(
 		luminanceChrominance,
-		centreSample.gb - half2(0.5),
+		centreSample.gb - half2(0.5f),
 		centreSample.a,
 		outTexture,
 		gid,
diff --git a/Outputs/ScanTargets/FilterGenerator.cpp b/Outputs/ScanTargets/FilterGenerator.cpp
index 0d52aa736..fb2516ff2 100644
--- a/Outputs/ScanTargets/FilterGenerator.cpp
+++ b/Outputs/ScanTargets/FilterGenerator.cpp
@@ -30,32 +30,35 @@ float FilterGenerator::radians_per_sample() const {
 FilterGenerator::FilterPair FilterGenerator::separation_filter() {
 	FilterPair result{};
 
-	// Luminance: box.
+	// Luminance.
 	result.luma =
-//		SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
-//			max_kernel_size_,
-//			samples_per_line_,
-//			0.0f,
-//			subcarrier_frequency_ * 0.25f
-//		);
 		SignalProcessing::Box::filter<SignalProcessing::ScalarType::Float>(
 			radians_per_sample(),
 			std::numbers::pi_v<float> * 2.0f
 		);
 
-	// Chrominance: compute as subcarrier - luminance.
-
-	// TODO: attempting a notch as below seems to introduce a phase shift or time delay.
-	// I'm not smart enough currently to understand why.
-	// I need to fix or, at the minimum, predict it for correction later.
+//	Usually provides a better luminance filter, but has issues with in-phase NTSC colour:
+//
+//		SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
+//			max_kernel_size_,
+//			samples_per_line_,
+//			0.0f,
+//			subcarrier_frequency_ * 0.5f
+//		);
 
+	// Chrominance.
 	result.chroma = SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
 		max_kernel_size_,
 		samples_per_line_,
 		subcarrier_frequency_,
 		samples_per_line_
 	);
-	result.luma.copy_to<SignalProcessing::FIRFilter<SignalProcessing::ScalarType::Float>::iterator>(
+	SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
+		max_kernel_size_,
+		samples_per_line_,
+		0.0f,
+		subcarrier_frequency_
+	).copy_to<SignalProcessing::FIRFilter<SignalProcessing::ScalarType::Float>::iterator>(
 		result.chroma.begin(),
 		result.chroma.end(),
 		[](const auto iterator, const float value) {
@@ -69,30 +72,36 @@ FilterGenerator::FilterPair FilterGenerator::separation_filter() {
 FilterGenerator::FilterPair FilterGenerator::demouldation_filter() {
 	FilterPair result{};
 
-	result.chroma =
-		SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
-			max_kernel_size_,
-			samples_per_line_,
-			40.0f,
-			subcarrier_frequency_ * 0.5f
-		)
-		* (decoding_path_ == DecodingPath::SVideo ? 2.0f : 0.5f);
-
-	// S-Video: don't filter luminance at all.
 	if(decoding_path_ == DecodingPath::SVideo) {
+		// S-Video: don't filter luminance at all.
 		const float identity[] = { 1.0f };
 		result.luma =
 			SignalProcessing::FIRFilter<SignalProcessing::ScalarType::Float>(
 				std::begin(identity),
 				std::end(identity)
 			);
-		return result;
+	} else {
+		// Composite: sharpen the luminance a touch.
+		result.luma =
+			SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
+				max_kernel_size_, samples_per_line_, 100.0f, subcarrier_frequency_);
 	}
 
-	// Composite: sharpen the luminance a touch.
-	result.luma =
-		SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
-			max_kernel_size_, samples_per_line_, 10.0f, subcarrier_frequency_);
+	result.chroma =
+		SignalProcessing::Box::filter<SignalProcessing::ScalarType::Float>(
+			radians_per_sample(),
+			std::numbers::pi_v<float> * 2.0f
+		)
+		* (decoding_path_ == DecodingPath::SVideo ? 2.0f : 0.5f);
+
+//	Usually provides a better chroma filter, but has issues with in-phase NTSC colour:
+//
+//		SignalProcessing::KaiserBessel::filter<SignalProcessing::ScalarType::Float>(
+//			max_kernel_size_,
+//			samples_per_line_,
+//			0.0f,
+//			subcarrier_frequency_ * 0.5f
+//		)
 
 	return result;
 }