Reto's Weblog

Optimizing PNG Compression

reto — Sun, 06 Jan 2008 22:49:56 +0100

While creating some screenshots and saving them with the GIMP, I felt the PNG files were rather big and I was looking for a tool that would do better compression. PNG files usually are saved with lossless compression, not like JPEG files, where you always loose some image information with every percent of higher compression.

As usual googling helped and I quickly found the two very handy command line tools pngcrush and pngnq. pngcrush is an optimizer for PNG files and tries to create optimized PNG files without compromising their quality (e.g. as small as possible but lossless). pngnq on the other hand creates quantized PNG images, which means that the compression is not lossless anymore.

Both tools are available for various platforms such as Linux, Windows and Mac. As usual the ~~ubuntu-way~~ debian-way is straight forward and as easy as:

$ apt-get install pngnq pngcrush

The screenshots below illustrate the different qualities and file sizes to expect with default settings on all three tools. In some occasions individual tweaking may result in even better results, but the default settings work for me just fine in this case.

Summary on a 957x957 pixel screenshot:
Original (The GIMP, level 9): ~287 kb
Processed by pngcrush: ~284kb
Processed by pngnq: ~82kb

Screenshot saved with GIMP 2.4.2, compression level 9 (default/maximum) ~287kb:

Screenshot saved with GIMP and optimized with pngcrush ~284kb:

Screenshot saved with GIMP and quantized with pngnq ~82kb:

Conclusion: The GIMP has a rather effizient compression on level 9 as pngcrush could not achieve much better results (only about 1% reduced filesize). But you are limited to use lossless compression with the GIMP. So using pngnq may be usefull in some situations. The filesize reduction is usually significant (up to 70% as compared to the output of the GIMP).

Tweaking Firefox Tabs

reto — Tue, 23 Jan 2007 21:50:43 +0100

I found it quite annoying that the close-tab buttons () on each tab disappear if tabs get shrinked to the minimum (e.g. if horizontal scrolling of tabs gets activated because of the number of open tabs in one window).

Luckily FF let's you configure about anything related to the UI. It's only a matter of editing two config values to leave the close buttons visible all the time!

Open a new, empty tab and type about:config into the address bar. Search the two config entries "Browser.tabs.tabMinWidth" (defaults to 100) and "Browser.tab.tabClipWidth" (defaults to 140). While tabMinWidth defines the minimum width a tab can be shrinked to, tabClipWidth defines the minimum width where the close button is still displayed on unfocused tabs. If you change tabMinWidth to 101 and tabClipWidth to 100 tabs are always closeable with just one click. See the screenshots below for a better understanding of the issue.

Default Firefox 2.0 setting:

Custom Firefox 2.0 (tabs can always be closed with one click):

The setting in the about:config:

Enjoy!

Ubuntu PXE install via Windows

reto — Sat, 23 Dec 2006 23:10:21 +0100

This article expains in step by step instruction how to install Ubuntu over the network (although it's easy to adapt the how-to to other linux distros) via a Windows 2000/XP client.

Introduction

The Preboot Execution Environment (PXE) is nothing new, but rarely used in home office environments because it's most of the time easier to install any operating system from a CD, DVD or even a USB storage device. But what, if you have neither optical drives nor USB storage devices? The only requisites for a PXE installation are a working computer (any OS with TFTP Servers available will do) and Internet access.

The Problem

With the new Intel Southbridge (ICH8R) parallel ATA Drives are no longer supported by the chipset natively, which means most motherboard manufacturers add third party controllers on their boards to provide p-ata interfaces. These third party controllers however are not well supported on Linux at the moment. Especially not directly in the kernel, which means you would have to pre-compile your own installer to access any p-ata CD-Rom. Another reason for using PXE might be subnotebooks without CD/DVD-ROM. The only option you have there is an installation via USB or over the network (PXE).

Step 1: Prerequisites

First get yourself a copy of the free TFTP server by Philippe Jounin. Second we need the ubuntu installer files. Of course it doesn't make much sense to download one of the ubuntu CD images if we only need the small installer. The installer will choose the nearest mirror and download all the files needed automatically during the installation.
The browsable Ubuntu archives are at http://archive.ubuntu.com/ubuntu/dists/. But as we only need the installer, we can ftp to ftp://archive.ubuntu.com/ubuntu/dists/edgy/main/installer-i386/current/images/ and download the folder netboot (ignore any symlinks, they may give you errors during the download).
That's all we need to boot our Ubuntu installer over the network. Let's setup the TFTP server.

Step 2: Setting up a TFTP Server on Windows

Create a directory, preferably on your C Drive. We'll name it tftp for now.
copy the tftpd32.exe to c:tftp
Start the server by clicking on the exe
switch to the tab "DHCP Server" and fill in your network setup. Note that the PC you want to boot must be in the same Subnet. Enter pxelinux.0 as the boot file. The Screenshot on the right shows my setup.

Now we need to copy the Ubuntu netboot installer over to our tftp root directory:

copy the folder ubuntu-installer to c:tftp
copy the folder pxelinux.cfg from ubuntu-installer/i386/ to c:tftp
copy the file pxelinux.0 from ubuntu-installer/i386/ to c:tftp

This is how your tftp folder should look like:

c:tftppxelinux.cfgdefault
c:tftpubuntu-installeri386<some more files/folders>
c:tftppxelinux.0
c:tftptftpd32.exe

Step 3: Booting Ubuntu

To boot from tftp you may need to activate booting from the network interface in the BIOS. This may be done in the boot sequence settings or directly in the onboard ethernet device settings. After that, restart, lean back and watch the activities in the log viewer tab of the tftpd.

Note: Ubuntu will let you choose a mirror and download all the files you need. The whole procedure will work with any other debian flavour almost identically. There is a nice how to on doing a PXE install via Linux instead of windows at the CCC Wiki.

Googlebot and Site Redirects

reto — Thu, 02 Oct 2003 19:45:34 +0200

At a first glance it seems like there is nothing on the web, that can hide from beeing indexed by Google. Not only html but twelve(!) other filetypes are getting indexed at the moment.
But Google is much pickier as one could assume, whereas its reasons are evident and reasonable:

1. Redirects
Googlebot (Google's Spider) doesn't follow the "http/1.1 302 Found" status code (resource temporarily moved). Instead you should use a "http/1.1 301 Moved Permanently" header to make Google follow the redirect.
To make the long story short: If you're using PHP to do the redirect (and many are using PHP these days) you should add the status code header manually because PHP sends a 302 Found status code by default.

This stops Google and therefore is only usefull if your site is really under maintenance at the moment:


<?php

    header('Location: http://www.foo.com/bar/');

?>

This makes Google follow the redirect and index the Site:


<?php

  header('HTTP/1.1 301 Moved Permanently');

  header('Location: http://www.foo.com/bar/');

?>

If you prefer to do the redirects within an .htaccess file (on Apache, of course), you could do it like this. Every Request to foo.com/ is redirected to foo.com/bar/:


 #Redirect (this will result in a 301 permanently moved status code)

 RedirectMatch permanent ^/$ http://www.foo.com/bar/

I expect it's faster and less resource intensive to set up an .htaccess file because there is no need to parse any php code at all. Though it won't matter in most cases anyway. (untested assumption)

2. Sessions
Google doesn't follow links with a session attached. If you've enabled session.use_trans_sid in your php.ini you should check if Google is requesting the page. If your site displays fine without the use of sessions simply don't start one if google is visiting. ;-)


<?php

    // session is not started to serve google

    if( stristr( $_SERVER['HTTP_USER_AGENT'], 'google') === false )

    {

        session_start();

    }

?>

Add as many search engine bots as you like. A more sophisticated method (like regular expressions) is not needed here, but would of course work, too.

Some Tips and Tricks for your EPOC Device

reto — Tue, 22 Aug 2000 19:43:25 +0200

Shortcut Shift+Ctrl+Fn+S:
Creates a screenshot in mbm format.
Shortcut Fn+'app':
Creates a new file (e.g. type Fn+'Word' for a new Word file)
Shortcut Ctrl+Shift+E:
'Kills' the marked application if you are in the "open files / programs" dialog.
Shortcut: Ctrl+Tab:
Drive 'z' (ROM) is now browseable.
Extras bar:
If you rearrange the Extras bar, make sure you save the settings in the Shell.ini. Simply go to the Control Panel, hit "Extras bar" or "Enter" and close the dialog with "OK". Otherwise you will loose the settings when you do a soft reset.
User dictionary:
You can find the User.dic in c:\system\data\. It is a plain txt-file, which you can import in Word, edit and then export again.