As I wrote just a few posts ago I had discovered Qtpfsgui – an open source High Dynamic Range (HDR) image processing software that runs on Linux – and on Windows and MacOS too.

Now I had the chance to give it a try. Here it is how it went.

First of all I installed a fresh Ubuntu 7.04 (Feisty Fawn) replacing my oldish Debian Sarge on my Dell Latitude C400. I had no joy with the normal desktop install CD because the video controller of this old laptop requires some extra care but the alternate install CD was working fine running the installation in text mode. Don´t worry the installed operating system is fully graphical.

I needed Ubuntu because I wanted an easy ride with installing Qtpfsgui, and after reading it´s Website I learnt that Cyril Lavier has packaged Qtpfsgui for Ubuntu and installing the package is easy like a pie. And it was indeed…

The HDR work-flow in Qtpfsgui is quite similar to the one of Photomatix meaning that it has two major steps:

• creating the HDR image
• tone mapping the HDR image to LDR

Creating the HDR image in Qtpfsgui is quite straightforward: you click on the New HDR icon and select your input image or images.

You might modify a few mystic settings for creating the HDR but it is not really necessary:

Click on the Next button and you are set: your HDR image is generated.

Before you can go to the fun part – the tone mapping – you have to save the generated HDR image.

Tone mapping in Qtpfsgui – that can be started by clicking on the Tonemap the HDR button – has way much more possibilities than you find in Photomatix. Qtpfsgui implements several tone mapping algorithms (so called operators) that you can choose from. Furthermore you have the possibility to display several differently tone mapped images on the screen at the same time.
Just click on any of the tabs of the different operators, play around with the sliders and then click on Apply and your tone mapped image will appear.
The title of the image window holds the name of the operator and the values of each parameter you used to create the image. The same meaningful info is offered in the filename when you save your tone mapped LDR image.

I put here a sample screenshot that I captured when working with a HDR image generated from a single raw file (NEF actually since it was coming out of my Nikon D80).

With this single input image I got the most appealing results with the Fattal algorithm.

My original plan was to try to create a tone mapped image in Qtpfsgui that is similar to the one I created with Photomatix. Then I realized that it´s not possible due to the fact that the two tools are using different algorithms for tone mapping. However see below the closest matches:

For playing around with the different operators in Qtpfsgui I was using an output resolution of 512x… to save some time with the image generation. (Tone mapping can be quite CPU intensive.) When I was satisfied with the result of the Fattal tone mapping operator above I wanted to create the LDR image in its original size (10 megapixel). It took extremely long time – due to the poor resources of my old laptop – and I was pretty surprised because the resulted colours of the big picture were quite different from the small one´s.

This was Sunday morning when I wrote an email to Guiseppe Rota – who was writing and is still maintaining Qtpfsgui – asking him what I did wrong. When I was checking my email Sunday afternoon his answer was already in my mailbox. He suggested reading two threads on the topic on the Flickr Qtpfsgui discussion forum about this phenomena here and here. Could I have such a support for a commercial software?

Qtpfsgui resources:

• The official Qtpfsgui Web site on Sourceforge.net
• Online manual
• Tutorial on HDR and Qtpfsgui in Ubuntu