diff --git a/Outputs/OpenGL/ScanTarget.cpp b/Outputs/OpenGL/ScanTarget.cpp
index e1f093701..26edb868e 100644
--- a/Outputs/OpenGL/ScanTarget.cpp
+++ b/Outputs/OpenGL/ScanTarget.cpp
@@ -167,20 +167,21 @@ void ScanTarget::setup_pipeline() {
 		set_uniforms(ShaderType::QAMSeparation, *qam_separation_shader_);
 	}
 
-	// Pick a single zoom level to apply to the output, given the intended aspect ratio compared to the 4/3 this
-	// scan target halways uses, and the required output dimensions.
+	// Select whichever of a letterbox or pillarbox avoids cropping.
 	constexpr float output_ratio = 4.0f / 3.0f;
 	const float aspect_ratio_stretch = modals.aspect_ratio / output_ratio;
-	const float zoom = modals.visible_area.appropriate_zoom(aspect_ratio_stretch);
 
-	// TODO: Adjust origin to recentre content, given the zoom.
 	auto adjusted_rect = modals.visible_area;
-//	adjusted_rect.origin.x = (aspect_ratio_stretch * zoom - modals.visible_area.size.width) * 0.5f;
-//	adjusted_rect.origin.y -= (zoom - modals.visible_area.size.height) * 0.5f;
+	const float letterbox_scale = adjusted_rect.size.height / (adjusted_rect.size.width * aspect_ratio_stretch);
+	if(letterbox_scale > 1.0f) {
+		adjusted_rect.scale(letterbox_scale, 1.0f);
+	} else {
+		adjusted_rect.scale(1.0f, 1.0f / letterbox_scale);
+	}
 
 	// Provide to shader.
 	output_shader_->set_uniform("origin", adjusted_rect.origin.x, adjusted_rect.origin.y);
-	output_shader_->set_uniform("size", zoom, zoom / aspect_ratio_stretch);
+	output_shader_->set_uniform("size", 1.0f / adjusted_rect.size.width, 1.0f / adjusted_rect.size.height);
 
 	// Establish an input shader.
 	if(!existing_modals_ || existing_modals_->input_data_type != modals.input_data_type) {
diff --git a/Outputs/ScanTarget.hpp b/Outputs/ScanTarget.hpp
index c3146b09d..dbe82a646 100644
--- a/Outputs/ScanTarget.hpp
+++ b/Outputs/ScanTarget.hpp
@@ -40,7 +40,7 @@ struct Rect {
 		return size.width == 0.0f || size.height == 0.0f;
 	}
 
-	void expand(const float min_x, const float max_x, const float min_y, float max_y) {
+	void expand(const float min_x, const float max_x, const float min_y, const float max_y) {
 		origin.x = std::min(origin.x, min_x);
 		size.width = std::max(size.width, max_x - origin.x);
 
@@ -48,6 +48,18 @@ struct Rect {
 		size.height = std::max(size.height, max_y - origin.y);
 	}
 
+	/// Scales a rectange around its centre.
+	void scale(const float scale_x, const float scale_y) {
+		const float centre[] = {
+			origin.x + size.width * 0.5f,
+			origin.y + size.height * 0.5f,
+		};
+		size.width *= scale_x;
+		size.height *= scale_y;
+		origin.x = centre[0] - size.width * 0.5f;
+		origin.y = centre[1] - size.height * 0.5f;
+	}
+
 	float appropriate_zoom(const float aspect_ratio_stretch) const {
 		const float width_zoom = 1.0f / (size.width * aspect_ratio_stretch);
 		const float height_zoom = 1.0f / size.height;