naviquan

A new set of source images
(from top: EV 0, EV -2,
EV +2)

Qtpfsgui HDR Wizard -
Load Images dialog box

Qtpfsgui HDR Wizard -
Editing Tool

Qtpfsgui HDR Wizard - HDR
creation settings

Qtpfsgui HDR tone
mapping dialog box

Qtpfsgui HDR - Fattal tone mapping

Qtpfsgui HDR - Mantiuk tone mapping

Qtpfsgui HDR - Mantiuk tone mapping with minor
additional adjustments in Photoshop

HDR with Photomatix Pro Details Enhancer tone
mapping

No serious fan of HDR can skip Qtpfsgui - an open source software offering the "true" HDR workflow for image processing (if you are not sure what I mean by "true" HDR, please read High Dynamic Range Photography - "HDR Look" and Pseudo HDR vs. HDR). Since late April of 2009, a new version of Qtpfsgui, Ver. 1.9.3, is available.

As anything else, Qtpfsgui has pluses and minuses. Its big plus that it's completely free (distributed under GNU GENERAL PUBLIC LICENSE Ver. 2) and can be downloaded here. On the other hand, it offers all regular tools requited for effective handling of all steps associated with HDR process: (1) creating an HDR image, saving and loading it, and (2) tone mapping it to obtain LDR. In addition, the package allows for rotate and resize HDR images as well as applying projective transformations to HDR images. Tone mapping an HDR is done through a separate dialog box, called "Interactive Tone Mapping window" which uses the HDR as a source to create an LDR. See on the right side screenshots of various Qtpfsgui windows to generate HDR images and apply tone mapping.

As usually with this series of articles, I do not go into a laundry list of many features available in this HDR software (for example, source image alignment, anti-ghosting, etc.) and do not want to make comments on such features. Instead, I prefer to focus on big picture. And one of the unique features of this software is that it offers a number of methods (or operators as they are called) for tone mapping. They are (1) Mantiuk, (2) Fattal, (3) Drago, (4) Durand, (5) Reinhard '02 and '05, (6) Ashikhmin, (7) Pattanaik. I consider this feature as a big plus since it gives plenty of opportunity and options for tone mapping, a fun part of HDR. Unfortunately, I (or software) failed with Durand - a tone mapping method that is supposed to deliver the most realistic pictures.

As often the case with HDR, numerous settings in Tone Mapping window are quite intimidating, and information about their meaning is scarce. The tool authors (specialists of the highest order in HDR) answer this question in the following way: "To answer precisely this question one would have to explain the inner workings of the tone mapping operator X, in terms of the original research paper. At the end of the day all that matters (to some people, at least) is to fiddle with the settings until you obtain a nice result."

Whether it's minus or not, but tone mapping process does not offer a preview; instead, another approach is implemented to facilitate that fiddling with parameters. In particular, you can generate different sizes of LDR images where the smallest one, 256x170 can be processed very quickly. In addition, when you change a setting, Qtpfsgui tone mapping does not override the LDR images generated with other settings. Instead, it adds images to the workspace so that you have a chance to compare all of them. At first, this approach seemed odd, but I quickly developed a taste for it.

Basically, I ended up in generating quickly a series of small images with different settings - that can be as many as 20 - 30 images (it all depends on how many parameters are available for a tone mapping operator). The View option of the main menu allows to tile or cascade them so that you can very quickly identify the range of values which produces results you like most. Then, you can refined settings with generating bigger images (like 768x510). I found this process (of narrowing down settings to what you like and what is good for a particular picture) a good substitution for previewing and in many cases even more practical. What helps in this process is that you do not need to take notes of which LDR image was created with what settings - window titles list conveniently all values (as seen here). Add to this, there is an option of Save All that allows to save all LDR images in the current workspace with files names that start with the tone mapping name and all values of settings used. There is one caveat with all this you need to keep in mind - you cannot rely automatically on the assumption that bigger LDR image produced with same settings as its smaller version will be simply its enlarged copy. This is because the size of the image itself is usually a parameter used in tone mapping process.

In my view, out seven tone mapping operators, most photographers (who are after that special HDR look) will find two of them most interesting: Mantiuk and Fattal. By the way, for this installment of the article, I decided to abandon for a moment that dull image of dark room, and decided to use something more exciting - pictures of Great Falls, Virginia. You can see source images on the left side (top) and results obtained with Qtpfsgui and its Mantiuk and Fattal tone mapping operators on the right side. Click on thumbnails to enlarge them - you will have to agree that indeed the HDR look is there.

Obviously, both results are very far from reality. But if that's what you want, I would recommend to spend most your time playing with Fattal tone mapping used by most users to produce pictures with stunning effects. Not a surprise, one of the reasons for that are smaller details significantly amplified by Fattal. One of the unwanted consequences of this is that noise will be amplified as well - keep this in mind when trying to use this method with noisy photos. Here are quick tips regarding Fattal settings:

• Alpha - increasing the value will result in accentuated details
• Beta - decreasing beta you will increase the effectiveness of the algorithm: meaning that low values result in details more pronounced over the rest of the image. Increasing beta will result in more realistic picture.
• Color saturation - lower values result in less saturated colors
• Noise reduction is what it says. Keep in mind that even minor increase in noise reduction setting will significantly impact the result (effectively offsetting the detail accentuating properties of the tone mapping method). My recommendation - keep it at zero or in any case do not go beyond 0.001 or 0.002

To finish discussion about parameters for Fattal (and for that matter for any other tone mapping method) - my recommendation is to start with default values they are usually produce good results.

Based on my experience with using Qtpfsgui tone mapping, here are two tips I can give you:
     - Do not forget about a small button called "Adjust Levels..." (available on the tool bar); it can significantly change and improve your LDR
     - Nobody prevents you from further processing of your LDR images in Photoshop. In fact, on my right side bar I should how Mantuik tone mapping (interesting but still not exciting) can be improved in seconds with several click in Photoshop (in this case adjusting levels and color balance - imagine what could be done with more clicks!).

Finally, I cannot but try to compare somehow results obtained with Qtpfsgui 1.9.3 (Fattal and Mantiuk) and Photomatix Pro 3.1. To this end, I used same source images with Details Enhancer. I never tried to perfect output in either case - I just wanted to be practical to see what can be done quickly. Well, you decide what you like more - see images on the right side bar - as far as I am concerned, all of them are weird.

Part I - High Dynamic Range Photography Simplified
Part II - High Dynamic Range Photography - Photomatix Pro
Part III - High Dynamic Range Photography - "HDR Look" and Pseudo HDR vs. HDR