From 2384a876626c04c0223d89b56592a26073eebfc4 Mon Sep 17 00:00:00 2001
From: Julian Waller <git@julusian.co.uk>
Date: Thu, 15 Aug 2024 22:44:18 +0100
Subject: [PATCH] wip: add more constants

---
 src/lib/converters/colorConstants.ts | 12 +++++++++---
 src/lib/converters/yuv422ToRgba.ts   |  3 +--
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/lib/converters/colorConstants.ts b/src/lib/converters/colorConstants.ts
index 67990ed3..bddb8bec 100644
--- a/src/lib/converters/colorConstants.ts
+++ b/src/lib/converters/colorConstants.ts
@@ -13,6 +13,9 @@ export interface ColorConvertConstants {
 	readonly YOffset: number
 	readonly CbCrOffset: number
 
+	readonly KRKRioKG: number
+	readonly KBKBioKG: number
+
 	readonly KRoKBi: number
 	readonly KGoKBi: number
 	readonly KBoKRi: number
@@ -20,10 +23,10 @@ export interface ColorConvertConstants {
 }
 
 function createColorConvertConstants(KR: number, KB: number): ColorConvertConstants {
-	const KG = 1 - KR - KB
+	const KG = 1 - KR - KB // 0.7152
 
-	const KRi = 1 - KR
-	const KBi = 1 - KB
+	const KRi = 1 - KR // 0.7874 -> 1.5748
+	const KBi = 1 - KB // 0.9278 -> 1.8556
 
 	const YRange = 219
 	const CbCrRange = 224
@@ -44,6 +47,9 @@ function createColorConvertConstants(KR: number, KB: number): ColorConvertConsta
 		YOffset: 16 << 8,
 		CbCrOffset: 128 << 8,
 
+		KRKRioKG: (KR * KRi * 2) / KG,
+		KBKBioKG: (KB * KBi * 2) / KG,
+
 		KRoKBi: (KR / KBi) * HalfCbCrRange,
 		KGoKBi: (KG / KBi) * HalfCbCrRange,
 		KBoKRi: (KB / KRi) * HalfCbCrRange,
diff --git a/src/lib/converters/yuv422ToRgba.ts b/src/lib/converters/yuv422ToRgba.ts
index 38ac5552..e66fd56d 100644
--- a/src/lib/converters/yuv422ToRgba.ts
+++ b/src/lib/converters/yuv422ToRgba.ts
@@ -33,8 +33,7 @@ export function convertYUV422ToRGBA(width: number, height: number, data: Buffer)
 		a10: number
 	): [r: number, g: number, b: number, a: number] => {
 		const r = clamp(Math.round(y8 + constants.KRi * cr8))
-		// TODO - use more constants
-		const g = clamp(Math.round(y8 - ((0.2126 * 1.5748) / 0.7152) * cr8 - ((0.0722 * 1.8556) / 0.7152) * cb8))
+		const g = clamp(Math.round(y8 - constants.KRKRioKG * cr8 - constants.KBKBioKG * cb8))
 		const b = clamp(Math.round(y8 + constants.KBi * cb8))
 		const a = Math.round(a10)