Flip direction of y axis

Thanks https://mastodon.social/@jgilbert/113029443306185312

Author: simonw

gemini-bbox.html

@@ -171,7 +171,7 @@
 
                     // Y-axis labels and ticks
                     for (let i = 0; i <= 1000; i += 100) {
-                        const y = 20 + (1000 - i) / 1000 * image.height;
+                        const y = 20 + i / 1000 * image.height;
                         ctx.fillText(i.toString(), 75, y + 5);
                         ctx.beginPath();
                         ctx.moveTo(75, y);