ascii-cat.ts

/**
 * MIT License
 *
 * Copyright (c) 2024 Trevor Manz
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
import * as cli from "jsr:@std/[email protected]";
import { Image } from "https://deno.land/x/[email protected]/mod.ts";

let ASCII_CHARS = " .:-=+*#%@" as const;
let CHAR_ASPECT_RATIO = 0.45 as const;
let BRIGHTNESS_THRESHOLD = 200 as const; // thresh whether image is bright

function getAsciiChar(
	r: number,
	g: number,
	b: number,
	invert: boolean,
): string {
	let value = (r + g + b) / 3;
	let index = Math.floor(value / 25.6);
	return invert
		? ASCII_CHARS[ASCII_CHARS.length - 1 - index]
		: ASCII_CHARS[index];
}

function calcAverageBrightness(image: Image): number {
	let totalBrightness = 0;
	for (let y = 1; y <= image.height; y++) {
		for (let x = 1; x <= image.width; x++) {
			let [r, g, b] = image.getRGBAAt(x, y);
			totalBrightness += (r + g + b) / 3;
		}
	}
	let avgBrightness = totalBrightness / (image.width * image.height);
	return avgBrightness;
}

async function imageToAscii(
	path: string,
	options: { width: number },
): Promise<string> {
	let image = await Image.decode(await Deno.readFile(path));
	let aspectRatio = image.width / image.height / CHAR_ASPECT_RATIO;
	let out = image.resize(
		options.width,
		Math.floor(options.width / aspectRatio),
	);
	let invert = calcAverageBrightness(out) > BRIGHTNESS_THRESHOLD;

	let text = "";
	for (let y = 1; y <= out.height; y++) {
		for (let x = 1; x <= out.width; x++) {
			let [r, g, b] = out.getRGBAAt(x, y);
			text += getAsciiChar(r, g, b, invert);
		}
		text += "\n";
	}
	return text;
}

if (import.meta.main) {
	let args = cli.parseArgs(Deno.args, {
		string: ["width"],
		default: { width: "100" },
	});
	let path = args._[0];
	let width = parseInt(args.width);
	if (!path) {
		console.error(
			"Usage: deno run -R -N ascii-cat.ts <image-path> [--width <width>]",
		);
		Deno.exit(1);
	}
	try {
		let text = await imageToAscii(String(path), { width });
		Deno.stdout.writeSync(new TextEncoder().encode(text));
	} catch (error) {
		console.error("Error: " + error.message);
		Deno.exit(1);
	}
}