wip

better handling of reserved color

Makefile

@@ -20,4 +20,7 @@ all : sample0.xex \
 clean :
 	rm -f *.o
 	rm -f *.s.png
+	rm -f sample[0-9].s
+	rm -f fruit.s mapclock.s sailboat.s sunset.s train404.s
+	rm -f potato.s selfie.s kitty.s meme.s
 	rm -f *.xex

dither-image.js

@@ -28,6 +28,17 @@ function fromLinear(val) {
     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;
     if (val <= 0.0031308) {
@@ -57,6 +68,39 @@ class RGB {
         return new RGB(r,g,b);
     }
 
+    static fromGTIA(val) {
+        // This seems off from what Atari800 does
+        // https://forums.atariage.com/topic/107853-need-the-256-colors/page/2/#comment-1312467
+        let cr = (val >> 4) & 15;
+        let lm = val & 15;
+        let crlv = cr ? 50 : 0;
+
+        /*
+        let phase = ((cr - 1) * 25 - 58) * (2 * Math.PI / 360);
+
+        let y = 255 * (lm + 1) / 16;
+        let i = crlv * Math.cos(phase);
+        let q = crlv * Math.sin(phase);
+
+        let r = y + 0.956 * i + 0.621 * q;
+        let g = y - 0.272 * i - 0.647 * q;
+        let b = y - 1.107 * i + 1.704 * q;
+        */
+
+        // PAL
+        let phase = ((cr - 1) * 25.7 - 15) * (2 * Math.PI / 360);
+
+        let y = 255 * (lm + 1) / 16;
+        let i = crlv * Math.cos(phase);
+        let q = crlv * Math.sin(phase);
+
+        let r = y + 0.956 * i + 0.621 * q;
+        let g = y - 0.272 * i - 0.647 * q;
+        let b = y - 1.107 * i + 1.704 * q;
+
+        return new RGB(r, g, b).clamp().fromSRGB();
+    }
+
     map(callback) {
         return new RGB(
             callback(this.r),
@@ -65,14 +109,18 @@ class RGB {
         );
     }
 
-    toLinear() {
+    fromNTSC() {
         return this.map(toLinear);
     }
 
-    fromLinear() {
+    toNTSC() {
         return this.map(fromLinear);
     }
 
+    fromSRGB() {
+        return this.map(fromSRGB);
+    }
+
     toSRGB() {
         return this.map(toSRGB);
     }
@@ -134,13 +182,24 @@ class RGB {
             this.b * this.b;
     }
 
+    sum() {
+        return this.r + this.g + this.b;
+    }
+
+    lumaScale() {
+        return new RGB(
+            this.r * 0.299,
+            this.g * 0.586,
+            this.b * 0.114
+        );
+    }
+
     luma() {
-        return this.r * 0.299 + this.g * 0.587 + this.b * 0.114;
+        return this.lumaScale().sum();
     }
 }
 
-const maxDist = (new RGB(255, 255, 255)).magnitude();
+/*
-
 // snarfed from https://lospec.com/palette-list/atari-8-bit-family-gtia
 // which was calculated with Retrospecs App's Atari 800 emulator
 let atariRGB = [
@@ -400,8 +459,16 @@ let atariRGB = [
     0xf6e46f,
     0xfffa84,
     0xffff99,
-].map((hex) => RGB.fromHex(hex).toLinear());
+].map((hex) => RGB.fromHex(hex).fromNTSC());
 //].map((hex) => RGB.fromHex(hex));
+*/
+
+let atariRGB = [];
+for (let i = 0; i < 256; i++) {
+    atariRGB[i] = RGB.fromGTIA(i);
+}
+
+
 
 /**
  * Dither RGB input data with a target palette size.
@@ -414,19 +481,6 @@ let atariRGB = [
  * @returns {{output: number[], palette: number[], error: RGB[]}}
  */
 function decimate(input, palette, n) {
-    // to brute-force, the possible palettes are:
-    // 255 * 254 * 253 = 16,386,810
-    //
-    // we could brute force it but that's a lot :D
-    // but can do some bisection :D
-    //
-    // need a fitness metric.
-    // each pixel in the dithered line gives a distance
-    // sum/average them? median? maximum?
-    // summing evens out the ups/downs from dithering
-    // but doesn't distinguish between two close and two distant options
-    // consider median, 90th-percentile, and max of abs(distance)
-    // consider doing the distance for each channel?
 
     let width = input.length;
 
@@ -440,7 +494,6 @@ function decimate(input, palette, n) {
 
     // Apply dithering with given palette and collect color usage stats
     let dither = (palette) => {
-        let fitness = zeroes(width);
         let error = {
             cur: [],
             next: [],
@@ -467,7 +520,7 @@ function decimate(input, palette, n) {
 
             for (let i = 0; i < palette.length; i++) {
                 let diff = rgb.difference(atariRGB[palette[i]]);
-                let dist = diff.magnitude2();
+                let dist = diff.magnitude();
                 if (dist < shortest) {
                     nextError = diff;
                     shortest = dist;
@@ -484,21 +537,10 @@ function decimate(input, palette, n) {
             error.next[x - 1]?.inc(share(3));
             error.next[x    ]?.inc(share(5));
             error.next[x + 1]?.inc(share(1));
-
-            let mag = nextError.magnitude();
-            fitness[x] = maxDist / mag;
-            // 442 is the 3d distance across the rgb cube
-            //fitness[x] = 442 - (nextError.magnitude());
-            //fitness[x] = 442 / (442 - nextError.magnitude());
-            fitness[x] = 255 / (256 - Math.max(0, nextError.r, nextError.g, nextError.b));
-
-            let mag2 = nextError.magnitude2();
-            distance2 += mag2;
         }
         return {
             output,
             palette,
-            fitness,
             distance2,
             popularity,
             error: error.next
@@ -538,7 +580,11 @@ function decimate(input, palette, n) {
 
     // Median cut!
     // https://en.wikipedia.org/wiki/Median_cut
-    let buckets = [input.slice()];
+    //let buckets = [input.slice()];
+
+    // preface the reserved bits
+    let buckets = reserved.slice().map((c) => [atariRGB[c]]).concat([input.slice()]);
+
     let medianCut = (bucket, range) => {
         if (bucket.length < 2) {
             console.log(bucket);
@@ -571,8 +617,23 @@ function decimate(input, palette, n) {
             );
         });
         let topRanges = ranges.map((rgb) => Math.max(rgb.r, rgb.g, rgb.b));
-        let greatest = Math.max(...topRanges);
+        //let greatest = Math.max(...topRanges);
-        let index = topRanges.indexOf(greatest);
+        //let index = topRanges.indexOf(greatest);
+        let greatest = 0;
+        let index = -1;
+        for (let i = 0; i < topRanges.length; i++) {
+            if (topRanges[i] >= greatest) {
+                greatest = topRanges[i];
+                index = i;
+            }
+        }
+        if (index == -1) {
+            // We just ran out of colors! Pad the buckets.
+            while (buckets.length < n) {
+                buckets.push([new RGB(0, 0, 0)]);
+            }
+            break;
+        }
         let [lo, hi] = medianCut(buckets[index], ranges[index]);
         buckets.splice(index, 1, lo, hi);
     }
@@ -604,9 +665,11 @@ function decimate(input, palette, n) {
         //let rgb = bucket[bucket.length - 1];
 
         // Take the luma-brightest color in the bucket
+        // wrong? bad
         //let rgb = bucket.slice().sort((a, b) => b.luma() - a.luma())[bucket.length - 1];
 
         // Take the median color in the bucket
+        // bad
         //let rgb = bucket[bucket.length >> 1];
 
         // Combine the brightest of each channel
@@ -682,7 +745,7 @@ function imageToLinearRGB(rgba) {
             rgba[i + 0],
             rgba[i + 1],
             rgba[i + 2]
-        ).toLinear());
+        ).fromSRGB());
     }
     return input;
 }

video/combine.sh

@@ -0,0 +1,9 @@
+ffmpeg \
+    -r 60000/1001 \
+    -i 'frames/dither-%04d.png' \
+    -i 'colamath-audio.wav' \
+    -ac 2 \
+    -ar 48000 \
+    -vf 'pad=w=640:h=360:x=52:y=20' \
+    -pix_fmt yuv420p \
+    -y colamath-dither.mp4

video/extract.sh

@@ -0,0 +1,17 @@
+set -a
+
+mkdir -p frames
+
+ffmpeg \
+    -i colamath-dv.avi \
+    -vf 'yadif=1,scale=160:200,crop=h=160' \
+    -an \
+    -y 'frames/colamath-%04d.png'
+
+ffmpeg \
+    -i colamath-dv.avi \
+    -vn \
+    -ac 1 \
+    -ar 15734 \
+    -acodec pcm_u8 \
+    -y 'colamath-audio.wav'

video/video.sh

@@ -0,0 +1,15 @@
+set -e
+
+for frame in frames/colamath-[0-9][0-9][0-9][0-9].png
+do
+    n="${frame#frames/colamath-}"
+    n="${n%.png}"
+    out="frames/dither-${n}"
+    last="${n:0-1}"
+    node ../dither-image.js "$frame" "$out" &
+    if (( last == 9 ))
+    then
+        wait
+    fi
+done
+wait