diff --git a/poptimal.js b/poptimal.js
index 80b7414..bbbb058 100644
--- a/poptimal.js
+++ b/poptimal.js
@@ -19,7 +19,9 @@ const CELL = 10;
 const MAG = 2;
 const WIDTH = 20;
 const HEIGHT = WIDTH;
-const VISIBLE_DOG = 1000;
+// number of pixels which have to be visible for a colour to be
+// mentioned in the alt text
+const VISIBLE_DOG = 400;
 
 function randomise_params() {
 	const palette_name = random.choice(Array.from(PALETTES.keys()));
@@ -190,16 +192,19 @@ async function main() {
 	const cfjson = await promises.readFile(argv.c);
   	const cf = JSON.parse(cfjson);
 
+        const ts = String(Date.now());
 
-
-  	const fn = argv.o || String(Date.now()) + '.png';
+  	const fn = (argv.o || ts) + '.png';
+	const jsfn = (argv.o || ts) + '.json';
 
   	const imgfile = cf['working_dir'] + '/' + fn;
+	const paramsfile = cf['working_dir'] + '/' + jsfn;
 
 	const params = randomise_params();
 	const colourf = params.palette === 'grayscale' ? cf['grayscale'] : cf['colour'];
 
 	const namer = new ColourNamer();
+	console.log(`Loading colours ${colourf}`);
 	await namer.load_colours(colourf);
 
 
@@ -216,7 +221,6 @@ async function main() {
  	const pngData = resvg.render();
   	const pngBuffer = pngData.asPng();
 
-
   	await promises.writeFile(imgfile, pngBuffer);
 
   	// generate the alt_text last to check the image file histogram
@@ -224,6 +228,7 @@ async function main() {
   	const hist = await get_histogram(imgfile);
 	const alt_text = image_description(namer, params, hist);
 
+	await promises.writeFile(paramsfile, JSON.stringify(params));
 	console.log(alt_text);
 	console.log(imgfile);
   	if( cf['base_url'] ) {