Working Version

2026-04-14 12:29:30 -07:00 · 2022-12-16 09:27:34 -05:00
commit ee6a9dc1a5
2 changed files with 77 additions and 0 deletions
--- a/index.html
+++ b/index.html
@@ -0,0 +1,77 @@
+<!DOCTYPE html>
+<html>
+
+<style>
+    .canvasstyle {
+        width: 90%;
+        object-fit: contain;
+        border: 1px solid black;
+    }
+</style>
+
+<script>
+
+    function dither(imageData) {
+        let output = new ImageData(imageData.width, imageData.height)
+        for (i = 0; i < imageData.data.length; i += 4) {
+            output.data[i] = output.data[i + 1] = output.data[i + 2] = Math.floor(imageData.data[i] * 0.3 + imageData.data[i + 1] * 0.59 + imageData.data[i + 2] * 0.11)
+            output.data[i + 3] = imageData.data[i + 3]
+        }
+        console.log("grey")
+
+
+        let slidingErrorWindow = [new Float32Array(imageData.width), new Float32Array(imageData.width), new Float32Array(imageData.width)]
+        const offsets = [[1, 0], [2, 0], [-1, 1], [0, 1], [1, 1], [0, 2]]
+
+        for (let y = 0, limY = imageData.height; y < limY; ++y) {
+            for (let x = 0, limX = imageData.width; x < limX; ++x) {
+                let i = ((y * limX) + x) * 4;
+                let accumulatedError = Math.floor(slidingErrorWindow[0][x])
+                let expectedMono = output.data[i] + accumulatedError
+                let monoValue = expectedMono
+                if (monoValue <= 127) {
+                    monoValue = 0
+                } else {
+                    monoValue = 255
+                }
+                let error = (expectedMono - monoValue) / 8.0
+                for (let q = 0; q < offsets.length; ++q) {
+                    let offsetX = offsets[q][0] + x
+                    let offsetY = offsets[q][1] + y
+                    if ((offsetX >= 0) && (offsetX < slidingErrorWindow[0].length))
+                        slidingErrorWindow[offsets[q][1]][offsetX] += error
+                }
+
+                output.data[i] = output.data[i + 1] = output.data[i + 2] = monoValue
+            }
+            // move the sliding window
+            slidingErrorWindow.push(slidingErrorWindow.shift())
+            slidingErrorWindow[2].fill(0, 0, slidingErrorWindow[2].length)
+        }
+        console.log("done")
+        return output
+    }
+
+    function setImage(src, target) {
+        let image = new Image()
+        image.onload = () => {
+            let gc = target.getContext("2d")
+            gc.drawImage(image, 0, 0, target.width, target.height)
+            let original = gc.getImageData(0, 0, target.width, target.height)
+
+            let dithered = dither(original)
+            gc.putImageData(dithered, 0, 0)
+        }
+        image.src = src
+    }
+
+    window.addEventListener("load", (e) => {
+        setImage("test.jpg", document.getElementById("drawing"))
+    })
+</script>
+
+<body>
+    <canvas id="drawing" class="canvasstyle" width="800" height="600"></canvas>
+</body>
+
+</html>
--- a/test.jpg
+++ b/test.jpg