From fe6314e2a0852959172a0d1ae7f1ccb79c4f16a5 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Fri, 24 Mar 2023 00:28:07 -0700
Subject: [PATCH] just use srgb for consistency with the pngs

---
 dither-image.js | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/dither-image.js b/dither-image.js
index ee313d0..2c9e252 100644
--- a/dither-image.js
+++ b/dither-image.js
@@ -13,6 +13,7 @@ function zeroes(n) {
     return arr;
 }
 
+/*
 function toLinear(val) {
     // use a 2.4 gamma approximation
     // this is BT.1886 compatible
@@ -27,6 +28,18 @@ function fromLinear(val) {
     unit **= (1 / 2.4);
     return unit * 255;
 }
+*/
+
+function fromSRGB(val) {
+    val /= 255;
+    if (val <= 0.04045) {
+        val /= 12.92;
+    } else {
+        val = ((val + 0.055) / 1.055) ** 2.4;
+    }
+    val *= 255;
+    return val;
+}
 
 function toSRGB(val) {
     val /= 255;
@@ -65,6 +78,7 @@ class RGB {
         );
     }
 
+    /*
     toLinear() {
         return this.map(toLinear);
     }
@@ -72,6 +86,11 @@ class RGB {
     fromLinear() {
         return this.map(fromLinear);
     }
+    */
+
+    fromSRGB() {
+        return this.map(fromSRGB);
+    }
 
     toSRGB() {
         return this.map(toSRGB);
@@ -410,7 +429,7 @@ let atariRGB = [
     0xf6e46f,
     0xfffa84,
     0xffff99,
-].map((hex) => RGB.fromHex(hex).toLinear());
+].map((hex) => RGB.fromHex(hex).fromSRGB());
 //].map((hex) => RGB.fromHex(hex));
 
 /**
@@ -667,7 +686,7 @@ function imageToLinearRGB(rgba) {
             rgba[i + 0],
             rgba[i + 1],
             rgba[i + 2]
-        ).toLinear());
+        ).fromSRGB());
     }
     return input;
 }