Archive for Internet

Image Optimization Guide

On the forum I administer, I am forced to run a tight attachment policy. Disk space doesn’t grow on trees. Occasionally this leads to questions about the small attachment size limit of 50 KiB. This guide is intended to clarify that this is not nearly as tiny as you might think. Note that although I’ll mention commands without much explanation for the sake of brevity, you’re always recommended to further explore the possibilities offered by those commands with the --help flag as well as by running man the-command-here.

First you need to ask yourself what kind of file type is appropriate, if you have the choice. On screenshots, the main purpose of attachments on my forum, you’ll often encounter large areas of uniform background colors. PNG is therefore almost invariably the right choice. Crop out everything but what’s relevant. JPEG is appropriate for more dynamic pictures such as photographs. If you want to do a lot with photographs, you might want to consider an external hosting service. My wife likes SmugMug. Still, for thumbnails you might be able to do a fair bit more within a few hundred KiB than you might think. Finally, the vector graphics in SVG result in pictures that always look sharp. You’ll typically have drawn these in a program like Inkscape or Adobe Illustrator.

Table of Contents

  1. 1. Optimizing JPEG
  2. 2. Optimizing PNG
  3. 3. Optimizing SVG
  4. Addendum A: Scanned Documents
  5. Addendum B: Video

1. Optimizing JPEG

Often you’ll want to crop your file. Do not edit your JPEG followed by resaving it because this will result in reduced quality! You can crop losslessly with cropgui. On Windows you can use IrfanView.

If you don’t want to crop, and also potentially for some post-cropgui optimization, use jpegtran -copy none -progressive -optimize file.jpg > file-opt.jpg. Note that this will get rid of all metadata, which may be undesirable. If so, use jpegtran -copy all -progressive -optimize file.jpg > file-opt.jpg.

Of course if you want to scale down your JPEG there’s no point in mucking about with lossless cropping first. After scaling down, check how long your quality can go (also see a little helper script I wrote). In any case, you should avoid introducing any unnecessary compression steps with associated quality loss. Here are some results:

  • The original 11.jpg at 2.19 MB.
  • Losslessly cropped 11-crop.jpg at 1.11 MB.
  • Optimized with -copy all -progressive -optimize 11-crop-opt.jpg at 1.04 MB. -copy none would’ve saved an extra whopping 40-some KiB, which on this kind of filesize has little benefit, and besides, I quite like the metadata. For thumbnail-sized files the balance is likely to be different. For example, the 52.2 KiB SmugMug auto-generated thumbnail below can be insignificantly reduced to 51.1 KiB with --copy all, but to 48.2 KiB with --copy none. I think an 8% reduction is not too shabby, plus it brings the file size down to under the arbitrary 50 KiB limit on my forum.

2. Optimizing PNG

As I wrote in the introduction, for screenshots PNG is typically the right choice. If you want to use lossless PNG, use optipng -o7. In my experience it’s ever so slightly smaller than other solutions like pngcrush. But as long as you use a PNG optimizer it shouldn’t much matter which one you fancy. Also see this comparison.

If you don’t care about potentially losing some color accuracy, use pngquant instead. To top it off, if you really want to squeeze out your PNG, you can pass quality settings with --quality min-max, meaning you can pass --quality 30-50 or just --quality 10. Here are some quick results for the screenshot in the SVG section below, but be sure to check out the pngquant website for some impressive examples.

$ du -h --apparent-size inkscape-plain-svg.png
27K	inkscape-plain-svg.png

$ du -h --apparent-size inkscape-plain-svg-fs8\ default.png 
7.6K	inkscape-plain-svg-fs8 default.png

$ du -h --apparent-size inkscape-plain-svg-fs8\ quality\ 10.png 
4.3K	inkscape-plain-svg-fs8 quality 10.png

In this case there is no visual distinction between the original PNG and the default pngquant settings. The quality 10 result is almost imperceptibly worse unless you look closely, so I didn’t bother to include a sample.

3. Optimizing SVG

For using SVG on the web, I imagine I don’t have to tell you that in Inkscape, you should save your file as Plain SVG.

Save as Plain SVG in Inkscape.

What you may not know is that just like there are lossy PNGs, you can also create what amounts to lossy SVGs. There are some command-line tools to optimize SVGs, including (partially thanks to this SO answer):

  • Scour is probably the best command line tool for some quick optimization. You can just use the defaults like scour < in.svg > out.svg or scour -i in.svg -o out.svg. But I recommend you go further.
  • SVGO (SVG Optimizer)
  • SVG-optimiser (by Peter Collingridge)
  • SVG-editor (by Peter Collingridge

My personal preference for squeezing out every last byte goes toward the web-based version of the SVG-editor by Peter Collingridge. By running it in a browser with inferior SVG support such as Firefox, you’ll be sure that your optimized SVG still works properly afterward. The command line tools can only safely be used for basic optimizations, whereas the effects of going lossy (such as lowering precision) can only be fully appreciated graphically.

Addendum A: Scanned Documents

Scanned documents are a different item altogether. The best format for private use is DjVu, but for public sharing PDF is probably preferable. To achieve the best results, you should scan your documents in TIFF or PNG, followed by processing with unpaper or ScanTailor. If you’ve already got a PDF you’d like to improve, you can use pdfsandwich or my own readablepdf.

Addendum B: Video

I’m not aware of any lossless optimization for video compression such as offered by jpegtran, but you can often losslessly cut video. In the general purpose Avidemux, simply make sure both video and audio are set to copy. There is also a dedicated cross-platform app for lossless trimming of videos called, unsurprisingly, LosslessCut. If you do want to introduce loss for a smaller file size you can use the very same Avidemux with a different setting, ffmpeg, mpv, VLC, and so forth. You can get reasonable quality that’ll play many places with something like:

ffmpeg -i input-file.ext -c:v libx264 -crf 19 -preset slow -c:a libfaac -b:a 192k -ac 2 output-file.mp4

For the open WebM format, you can use along these lines:

ffmpeg -i input.mp4 -c:v libvpx -b:v 1M -c:a libvorbis output.webm

More examples on the ffmpeg wiki. Note that in many cases you should just copy the audio using -acodec copy, but of course that’s not always an option. Extra compression artifacts in audio detract significantly more from the experience than low-quality video.


Failing Automation is (Almost) Always Fun

Just so long as you don’t depend on it. In this case we’ve got Gmail’s automated translation feature, which I’ve probably only used once or twice in the past decade in order to see how it worked. Today it had the nice idea to suggest interference in English.

The original message. Must be French!
After translation. Yup, removing that one word really helped me understand this mysterious language.

There is in fact French text hiding in the conversation history. Funny thing though — there’s no suggestion to translate on any of the preceding or following messages that are actually in French. So it goes.

Comments (1)Tags:

Switching to FreshRSS

QuiteRSS is a terrific piece of software. It only has one flaw, which is that it only runs on my desktop. Unfortunately this has led to me increasingly getting behind on the things I like to read. Sometimes this is fine, like when I can read a book instead, but other times it’s mildly frustrating.

QuiteRSS in three-column mode.

It would seem that none of the online feeds readers, whether self-hosted or SaaS, support the paradigm I’m used to. They’re all following the “golden standard” of nightmarish, thankfully-it’s-gone Google Reader. Basically I use feeds like emails. Most I delete after reading. Those I want to keep for reference I keep around, marked read.

But not so with these feedreaders. Feeds you want to keep for later reading should preferably be favorited, bookmarked, or maybe saved to a system like Wallabag. This has advantages too, of course. By centralizing your to-read list in one location, like Wallabag or Pocket, you don’t have the problem of remembering what’s where, or that you have loads of unread open tabs in various browsers.

Long story short, after sampling a whole bunch of feedreaders I opted for FreshRSS. It suffers from the omnipresent “no pages” disease. Got a feed with a thousand items? (Yes, they exist.) You can go to the start or the beginning by sorting in ascending or descending order, but reading things somewhere down the middle? Forget it.

These minor inconveniences are worth it, however. This way I can easily read my feeds from any computer anywhere in the world. The feeds are always updated, provided you set up a cron job. I don’t have to start up my computer or risk missing anything if I’m on vacation for a few days. I can quickly check them on my cellphone during an otherwise wasted moment. Overall I’m happy. Goodbye, QuiteRSS. You were a good friend after Opera died, but it’s time to move on.

PS Here are some feed-related links that should go along nicely with any feed reader.

  • Feed Creator allows you to create feeds for webpages that are missing them.
  • So does RSS-Bridge, but since it’s self-hosted it fits perfectly next to FreshRSS in the kluit spirit.
  • Tubes is a tool I wrote a few years back that can filter and fix up feeds. Useful if a website happens to have a feed, but not on a per-category basis or some such. Or of course because you might want to subscribe to an hourly news podcast, but only get the news once a day.

CommentsTags: , , ,

SSH publickey denied?

I was suddenly having trouble connecting to GitHub, after pulling in an OpenSSH update to version 7. Chances are that means the problem is security-related, meaning it’s worthwhile to take the time to investigate the cause.

$ git pull
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

A little debugging showed the following:

$ ssh -vT
OpenSSH_7.1p2 Debian-2, OpenSSL 1.0.2f  28 Jan 2016
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to [] port 22.
debug1: Connection established.
debug1: Skipping ssh-dss key /home/frans/.ssh/id_dsa for not in PubkeyAcceptedKeyTypes
debug1: No more authentication methods to try.
Permission denied (publickey).

Of course I could quickly fix the problem by adding PubkeyAcceptedKeyTypes ssh-dss to ~/.ssh/config, but checking tells me that “OpenSSH 7.0 and greater similarly disables the ssh-dss (DSA) public key algorithm. It too is weak and we recommend against its use.” So, although I could obviously re-enable it easily, I guess I’ll have to generate a new key. I hope GitHub’s guide is accurate for generating something sufficiently secure, because I’m kind of ticked off that something I generated in 2013 is already considered “legacy.” I hope I’m to blame and not an earlier version of GitHub’s guide.

Incidentally, to change the passphrase one would use the -p option, e.g.:

ssh-keygen -f id_rsa -p


Custom page number count in Prince

Prince makes it really easy to do all of the usual things with page numbers, like a different numbering scheme in the front matter and whatnot. Unfortunately you can’t counter-increment on @page, but thanks to Prince.addScriptFunc() you’ve got something better.

h2 {counter-reset: page 50}

@page {
	@bottom-left {
		content: prince-script(fixpagenum, counter(page));
		margin-left: 2cm;

In this CSS, instead of passing regular generated content, we’re passing a prince-script. That script has to be defined somewhere, like this.

Prince.addScriptFunc("fixpagenum", function(pagenum) {
	pagenum = Number(pagenum);
	pagenum = pagenum + pagenum - 50;
	return pagenum;

The rationale in this case was to generate two separate documents, starting at page 50, one only left pages and the other only right pages. (Of course, the other one started at page 51.) I combined them with pdftk’s shuffle command.

pdftk left.pdf right.pdf shuffle output combined.pdf

I don’t think there’s a way to do something like this purely in Prince using CSS, but I’d love to be proved wrong.


Connecting to Belgacom FON: It’s Still Possible

I was happily using Belgacom FON Autologin instead of the behemoth of an official Belgacom app, but ever since Belgacom updated their portal code I’ve barely been able to connect at all. That’s Belgacom’s fault, not the app’s. I haven’t been able to connect through the web interface or the official app either, because it just times out or gives mysterious errors. Unfortunately Belgacom FON Autologin pretends to be a browser by sending information over the HTTP protocol, so it equally fails to connect.

Luckily I just came across FON AccessFon, an app that utilizes the WISPr protocol. In a magnificent 33 kB it manages to connect to Belgacom FON quickly and efficiently, and for every FON router rather than just Belgacom’s to boot.


How I Put Real Firefox on Debian

With a bit of trial and error it worked out like this. Alternatively you could use /opt.

Create a file called something like firefox.desktop in /home/username/.local/share/applications/

In that file, put:

[Desktop Entry]
GenericName=Web Browser
X-GNOME-FullName=Firefox Web Browser
Exec=/home/username/programs/firefox/firefox %u

To make it the default system-wide, manually add it to Xfce’s Preferred applications or your window manager’s equivalent. Also add it to Debian’s alternative system.

$ sudo update-alternatives --install /usr/bin/x-www-browser x-www-browser /home/username/programs/firefox/firefox 20
[sudo] password for username: 
$ sudo update-alternatives --config x-www-browser
There are 2 choices for the alternative x-www-browser (providing /usr/bin/x-www-browser).

  Selection    Path                                   Priority   Status
* 0            /usr/bin/iceweasel                      70        auto mode
  1            /home/monkey/programs/firefox/firefox   20        manual mode
  2            /usr/bin/iceweasel                      70        manual mode

Press enter to keep the current choice[*], or type selection number: 1
update-alternatives: using /home/monkey/programs/firefox/firefox to provide /usr/bin/x-www-browser (x-www-browser) in manual mode

It’s not very pretty, but it does the trick.


Stop Hijacking Annoyances

Here’s another rescue from My Opera. The script was compiled by the user pehage on February 3, 2012, after a quick pointer by me. It is Opera UserJS, so it won’t work in any other browser. Don’t forget to enable User JavaScript on HTTPS if you so desire. In Opera 12 it no longer pops up a warning all the time.

// ==UserScript==
// @name Stop Hijacking Annoyances
// @include *
// ==/UserScript==

var annoyances = ["focus", "focusin", "focusout", /*"click",*/ "dblclick", "mousedown", "mouseup", "mousemove", "mouseover", "mouseout", "mouseenter", "mouseleave", "select", "submit", "keydown", "keypress", "keyup"];

for (var i=0; i<annoyances.length; i++) {
	window.opera.addEventListener("BeforeEventListener." + annoyances[i], function (e) {
	}, false);

And here is a simple testcase I created.

<!DOCTYPE html>
<title>keypress hijacker</title>
document.addEventListener('keypress', function(e){alert('document.addEventlistener on keypress ' + String.fromCharCode(e.which))}, false);
window.onkeydown = function(e){alert('window.onkeydown ' + String.fromCharCode(e.which))}
This page hijacks keypress events in order to display an alert message.


Data URI Bookmarklet

This is a repost of something I wrote on My Opera forums on 8 January 2013. The My Opera forums will be shutting down on 1 March 2014.

The easiest method [to base64 encode an image] might be to use the newly supported (since v12) FileReader object, which has a readAsDataURL method. I wrote a quick proof of concept using XHR because I’m not really sure how else to get data to it (aside from a file input which is no good here). Alternatively you could load the image in a canvas and call toDataURL, but then you’ll lose stuff like metadata and I’m not even sure if the compression and such will remain the same.

var xhr = new XMLHttpRequest(),
	reader = new FileReader();'GET', location.href, true);
xhr.responseType = 'blob';
xhr.addEventListener('load', function () {
	if (xhr.status === 200) {
		reader.addEventListener('load', function (e) {
			location.href =;
		var responseWithMimeType = new Blob(new Array(xhr.response), {
			'type': xhr.getResponseHeader('Content-Type')

It does seem a bit roundabout, so I’d love to hear it if anyone has more efficient suggestions.

I just realized you may not be aware of how to make a bookmarklet. To save myself the effort of removing comments and such I used to obtain the following result:


Create a new bookmark, paste that into the URL and give it a nickname of your choice.

Easier still, just drag this or right-click, bookmark link: To Data URI. There might be some security restrictions on MyOpera against javascript links, so I’m not sure if it’ll work.

But for local files a simple page would do just fine. All you need is input type=”file” and a tiny bit of scripting similar to the above. Something like this should do:

<!DOCTYPE html>
<title>File to Data URL</title>

<input type="file">

var file = document.querySelector('input[type=file]'), reader = new FileReader();

file.addEventListener('change', function(e) {

reader.addEventListener('load', function(e) {
	location.href =;



Adding a User Font Size Preference to Simple Machines

Users should be able to choose their default font size easily through their browser, and their choice should be respected. But because all browsers default to 16px and most people never change the default, many sites—including Wikipedia—set their font-size to about 80% of that value to end up at a font size of 12px or 13px. Thus users might be prevented from lowering their font size on a site that actually respects their preferences if they so desire.

Because I don’t believe that either joining the 80% crowd or specifying a size in pixels is generally the right answer, I decided to add a user preference that overrides the font-size on the HTML element. For this to work as intended, your stylesheet needs to be entirely in percentages, em, rem, or use equivalent keywords like small and large.

First, in Admin > Configuration > Core Features, enable Advanced Profile Fields. Then, you can add custom profile fields in Admin > Configuration > Features and Options > Profile Fields. I added one named “Font size” with an input mask of /^[0-9]{1,3}(\.[0-9]{1,2})?(em|pt|px|%)$/.

Assuming your theme is based on the default, start editing index.template.php. Then, under the linked stylesheets you can put the override:

	// Custom user font-size
	if ($context['user']['is_logged']) {
		global $user_profile;
		if (!empty($user_profile[$context['user']['id']]['options']['cust_fontsi'])) {
			echo '
	<style>', 'html {font-size: ', $user_profile[$context['user']['id']]['options']['cust_fontsi'], '}', '</style>';

To find out exactly what kind of useful values you can obtain from e.g. $context and $user_profile, you can use var_dump($user_profile).


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