Remove the 'Threshold' node's "Luminance Calculation" parameter

editor/src/messages/portfolio/document/node_graph/node_properties.rs

@@ -1647,16 +1647,9 @@ pub(crate) fn threshold_properties(node_id: NodeId, context: &mut NodeProperties
 
 	let params: &[(ParameterRef, Color, f64)] = &[(MinLuminanceInput.into(), Color::BLACK, 50.), (MaxLuminanceInput.into(), Color::WHITE, 100.)];
 
-	let mut layout = Vec::with_capacity(3);
+	let mut layout = Vec::with_capacity(2);
 	build_shared_spectrum_section(node_id, context, params, &mut layout);
 
-	let luminance_calc = {
-		let mut info = ParameterWidgetsInfo::new(node_id, LuminanceCalcInput, true, context);
-		info.exposable = false;
-		enum_choice::<LuminanceCalculation>().for_socket(info).property_row()
-	};
-	layout.push(luminance_calc);
-
 	layout
 }
 

editor/src/messages/portfolio/document_migration.rs

@@ -2182,6 +2182,19 @@ fn migrate_node(node_id: &NodeId, node: &DocumentNode, network_path: &[NodeId],
 		}
 	}
 
+	// The Threshold node's luminance calculation input was retired
+	if reference == DefinitionIdentifier::ProtoNode(graphene_std::raster_nodes::adjustments::threshold::IDENTIFIER) && inputs_count == 4 {
+		let mut node_template = resolve_document_node_type(&reference)?.default_node_template();
+		document.network_interface.replace_implementation(node_id, network_path, &mut node_template);
+
+		let old_inputs = document.network_interface.replace_inputs(node_id, network_path, &mut node_template)?;
+
+		for (i, input) in old_inputs.iter().enumerate().take(3) {
+			document.network_interface.set_input(&InputConnector::node_at_index(*node_id, i), input.clone(), network_path);
+		}
+		inputs_count = 3;
+	}
+
 	if reference == DefinitionIdentifier::ProtoNode(graphene_std::repeat::repeat_on_points::IDENTIFIER) && inputs_count == 2 {
 		let mut node_template = resolve_document_node_type(&reference)?.default_node_template();
 		document.network_interface.replace_implementation(node_id, network_path, &mut node_template);

node-graph/nodes/raster/src/adjustments.rs

@@ -576,39 +576,61 @@ fn invert<T: Adjust<Color>>(
 #[node_macro::node(category("Raster: Adjustment"), properties("threshold_properties"), shader_node(PerPixelAdjust))]
 fn threshold<T: Adjust<Color>>(
 	_: impl Ctx,
-	#[implementations(
-		Raster<CPU>,
-		Color,
-		Gradient,
-	)]
+	#[implementations(Raster<CPU>, Color, Gradient)]
 	#[gpu_image]
 	image: Item<T>,
 	#[default(50.)] min_luminance: Item<PercentageF32>,
 	#[default(100.)] max_luminance: Item<PercentageF32>,
-	luminance_calc: Item<LuminanceCalculation>,
 ) -> Item<T> {
 	let mut image = image;
-	let min_luminance = min_luminance.into_element();
-	let max_luminance = max_luminance.into_element();
-	let luminance_calc = luminance_calc.into_element();
+	let min_luminance = min_luminance.into_element() / 100.;
+	let max_luminance = max_luminance.into_element() / 100.;
 
 	image.element_mut().adjust(|color| {
-		let min_luminance = srgb_to_linear(min_luminance / 100.);
-		let max_luminance = srgb_to_linear(max_luminance / 100.);
-
-		let luminance = match luminance_calc {
-			LuminanceCalculation::SRGB => color.luminance_rec_709(),
-			LuminanceCalculation::Perceptual => color.luminance_perceptual(),
-			LuminanceCalculation::AverageChannels => color.average_rgb_channels(),
-			LuminanceCalculation::MinimumChannels => color.minimum_rgb_channels(),
-			LuminanceCalculation::MaximumChannels => color.maximum_rgb_channels(),
-		};
+		// For PSD interop, we compare this 14-bit fixed-point Rec. 601 luma against the level unrounded
+		let [r, g, b, _] = color.to_gamma_srgb_channels();
+		let luminance = (4915. * r + 9667. * g + 1802. * b) / 16384.;
 
-		if luminance >= min_luminance && luminance <= max_luminance { Color::WHITE } else { Color::BLACK }
+		let output = if luminance >= min_luminance && luminance <= max_luminance { Color::WHITE } else { Color::BLACK };
+		output.with_alpha(color.a())
 	});
 	image
 }
 
+#[cfg(all(feature = "std", test))]
+mod threshold_tests {
+	use super::*;
+
+	/// Whether one gamma-space RGB value (0..255) ends up white at the given threshold level (0..255).
+	fn is_white(input: [f32; 3], level: f32) -> bool {
+		let pixel = Color::from_gamma_srgb_channels(input[0] / 255., input[1] / 255., input[2] / 255., 1.);
+		let result = threshold((), Item::new_from_element(pixel), (level / 255. * 100.).into(), 100_f32.into());
+		result.into_element().r() == 1.
+	}
+
+	#[test]
+	fn rec_601_luma_is_compared_as_an_8_bit_level() {
+		assert!(!is_white([200., 100., 40.], 128.));
+		assert!(!is_white([125., 130., 120.], 128.));
+		assert!(is_white([0., 255., 0.], 128.));
+		assert!(!is_white([255., 0., 0.], 128.));
+		assert!(is_white([128., 128., 128.], 128.));
+		assert!(!is_white([127., 127., 127.], 128.));
+		assert!(is_white([200., 100., 40.], 123.));
+		assert!(!is_white([200., 100., 40.], 124.));
+	}
+
+	#[test]
+	fn ties_follow_the_unrounded_fixed_point_luma() {
+		// Half-level lumas in 0.3/0.59/0.11 stay below the level either way, and the 14-bit weights pull a whole-level red or blue luma just under it
+		assert!(!is_white([189., 120., 0.], 128.));
+		assert!(!is_white([248., 90., 0.], 128.));
+		assert!(!is_white([135., 100., 0.], 100.));
+		assert!(!is_white([255., 0., 50.], 82.));
+		assert!(is_white([0., 200., 0.], 118.));
+	}
+}
+
 // Aims for interoperable compatibility with:
 // https://www.adobe.com/devnet-apps/photoshop/fileformatashtml/#:~:text=%27grdm%27%20%3D%20Gradient%20Map
 // https://www.adobe.com/devnet-apps/photoshop/fileformatashtml/#:~:text=Gradient%20settings%20(Photoshop%206.0)