From 0dcfa88c2991c25cb6d3eec315f071a6739a95bc Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Wed, 22 Mar 2023 23:24:11 -0700
Subject: [PATCH] wip

---
 dither-image.js | 85 +++++++++++++++++++++++++------------------------
 1 file changed, 44 insertions(+), 41 deletions(-)

diff --git a/dither-image.js b/dither-image.js
index 7ecd29d..f804df8 100644
--- a/dither-image.js
+++ b/dither-image.js
@@ -28,6 +28,17 @@ function fromLinear(val) {
     return unit * 255;
 }
 
+function toSRGB(val) {
+    val /= 255;
+    if (val <= 0.0031308) {
+        val *= 12.92;
+    } else {
+        val = (val * 1.055) ** (1.0 / 2.4) - 0.055;
+    }
+    val *= 255;
+    return val;
+}
+
 class RGB {
     constructor(r, g, b) {
         this.r = r;
@@ -46,41 +57,32 @@ class RGB {
         return new RGB(r,g,b);
     }
 
-    toLinear() {
+    map(callback) {
         return new RGB(
-            toLinear(this.r),
-            toLinear(this.g),
-            toLinear(this.b)
+            callback(this.r),
+            callback(this.g),
+            callback(this.b)
         );
     }
 
+    toLinear() {
+        return this.map(toLinear);
+    }
+
     fromLinear() {
-        return new RGB(
-            fromLinear(this.r),
-            fromLinear(this.g),
-            fromLinear(this.b)
-        );
+        return this.map(fromLinear);
     }
 
-    cap() {
-        if (this.r < 0) {
-            this.r = 0;
-        }
-        if (this.g < 0) {
-            this.g = 0;
-        }
-        if (this.b < 0) {
-            this.b = 0;
-        }
-        if (this.r > 255) {
-            this.r = 255;
-        }
-        if (this.g > 255) {
-            this.g = 255;
-        }
-        if (this.b > 255) {
-            this.b = 255;
-        }
+    toSRGB() {
+        return this.map(toSRGB);
+    }
+
+    clamp() {
+        return this.map((val) => {
+            if (val < 0) return 0;
+            if (val > 255) return 255;
+            return val;
+        });
     }
 
     inc(other) {
@@ -90,11 +92,11 @@ class RGB {
         return this;
     }
 
-    static add(a, b) {
+    add(other) {
         return new RGB(
-            a.r + b.r,
-            a.g + b.g,
-            a.b + b.b
+            this.r + other.r,
+            this.g + other.g,
+            this.b + other.b
         );
     }
 
@@ -399,6 +401,7 @@ let atariRGB = [
     0xfffa84,
     0xffff99,
 ].map((hex) => RGB.fromHex(hex).toLinear());
+//].map((hex) => RGB.fromHex(hex));
 
 /**
  * Dither RGB input data with a target palette size.
@@ -430,10 +433,9 @@ function decimate(input, palette, n) {
     let inputPixel = (x, error) => {
         let rgb = input[x].clone();
         if (error) {
-            rgb.inc(error.cur[x]);
+            rgb = rgb.add(error.cur[x]);
         }
-        rgb.cap();
-        return rgb;
+        return rgb.clamp();
     };
 
     // Apply dithering with given palette and collect color usage stats
@@ -585,7 +587,7 @@ function decimate(input, palette, n) {
         let lumas = bucket.map((rgb) => rgb.luma());
         let brightest = Math.max(...lumas);
         if (avg_luma > 0) {
-            rgb = rgb.multiply(brightest / avg_luma);
+            rgb = rgb.multiply(brightest / avg_luma).clamp();
         }
 
     
@@ -740,7 +742,7 @@ async function convert(source) {
             .slice(y * width, (y + 1) * width);
         if (y > 0) {
             let error = lines[y - 1].error;
-            inputLine = inputLine.map((rgb, x) => RGB.add(rgb, error[x]));
+            inputLine = inputLine.map((rgb, x) => rgb.add(error[x]));
         }
         let line = decimate(inputLine, allColors, 4, y);
         lines.push(line);
@@ -897,11 +899,12 @@ async function saveImage(width, height, lines, dest) {
             if (i >= width) {
                 throw new Error('i >= width');
             }
-            let rgb = atariRGB[palette[output[i]]];
+            //let rgb = atariRGB[palette[output[i]]].fromLinear();
+            let rgb = atariRGB[palette[output[i]]].toSRGB();
 
-            rgba[y * stride + x * 4 + 0] = fromLinear(rgb.r);
-            rgba[y * stride + x * 4 + 1] = fromLinear(rgb.g);
-            rgba[y * stride + x * 4 + 2] = fromLinear(rgb.b);
+            rgba[y * stride + x * 4 + 0] = rgb.r;
+            rgba[y * stride + x * 4 + 1] = rgb.g;
+            rgba[y * stride + x * 4 + 2] = rgb.b;
             rgba[y * stride + x * 4 + 3] = 255;
         }
     }