Best Free High Dynamic Range (HDR) Software

You needn't have bothered. Your digital photograph will be a flop. Either the painting will be dark and barely visible, or the window will appear as a glaring and dominant white area that is hardly recognizable as a window. Or both.

Digital photography is a wonderful technology, but it's not very good at handling scenes that are comprised of both very dark and very brightly-lit areas. The human eye is superb at this, but the sensors in digital cameras are not.

But, there is way to overcome this problem; It's called HDR photography. HDR photography works by combining several photos of the same scene, taken at different exposure settings, into one photo. The details of dark areas (from a longer-duration exposure) are combined with the details of brightly lit areas (from a shorter-duration exposure). The result is a single photo that is correctly exposed in both the dark and light areas; it not only looks like it is correctly exposed, it also looks more dimensional.

There is a related technique called tone mapping. I won't attempt to explain this, but you can read more about that here. I'm also aware that the newer concept is to tone map just a single image, and most of the available HDR software will allow you to do this.  The unfortunate thing is that it has become fashionable to have high saturation on tone mapping and I think this spoils an image.

To create HDR photographs you will need to do two things. First, it would be wise to use a tripod when you take your series of differently exposed photos, which will ensure that all of the photos are identically composed. Second, you need to combine the series of photos by using special HDR software. HDR is now part of the camera's features, like the new Pentax K-7.  I haven't seen how this works personally, but I suspect it is using several ev settings, but the sensors are also getting more sophisticated and will allow you to acknowledge different variations in light and adjust accordingly.

Taking the multiple shots may be easy, because most modern cameras have a "bracketing mode" that will allow you to automatically take a picture repeatedly at different exposures. However, if your camera doesn't have this "automatic" feature, you can do it manually. Check your camera's guidebook.

There are several free HDR software packages, and I've had the opportunity to review most of them. Selecting the best was not easy.

Qtpfsgui came out slightly ahead. It has great tone-mapping and aligning facilities, allows 8,16 and 32 bit channels and two means of manually manipulating the image. Qtpfsgui creates a wonderful range of tone-mapped HDR images. When loaded, the images can be aligned either automatically and manually. Click next and a wizard walks you through recommended profiles or you can change this to get the best profile for your image. It gives you choices for ghosting and response curves, and if these are not to your liking you can tick the custom configuration. After the generated image has been achieved, you have at your disposal a good array of tone-mapped filters and the ability to adjust tone-mapping manually. Here's the big hint; if your computer is struggling create the image in the smallest size. After you adjust your levels and find that you are satisfied with the finished image, delete it (yes, that's right, delete it!) and create your large one. This is not just Windows software; it can be used on Linux and Mac operating systems with support for RAW format.

Picturenaut provides (all automatically) image alignment, exposure correction, color balancing, noise level compensation, and derivation of the camera curve from the source images. Although it doesn't support bracketed RAW images, the many HDR formats it does support are:
PFM (Portable Float Map)
HDR (Radiance)
EXR (OpenEXR)
TIFF (32-bit Floating Point)
TIFF (LogLuv)
LDR
JPEG
TIFF (only RGB color space)
TGA (Targa, no alpha channel)

What is interesting is that this software provides a choice of "weighting" when you have loaded your images, offering options "Derivative", "+hat1", and "+hat2".

Simply explained, weighting defines the values between dark pixels and light pixels. Dark pixels have noise in them and light pixels are usually over-exposed; instead of dropping these pixels, they are assigned a weight value. Depending on your image, the weight function may help you obtain a better result. The EV (Exposure Value) can be taken from the EXIF information attached to the image, or assigned a manual value (this is excellent for cheating HDR's). As a modular piece of software, its most important functions can all be accessed from a command line. The downside is that you cannot alter the alignment of the image, but I have done tests on auto alignments and Picturenaut came out the best.  If you are looking for straight forward images without excessive tone mapping this has to be your top software.

FDRTools Basic was close to being my first choice because you are able to use the RAW format, and alter the image alignment. The supported import image formats are: JPEG, TIFF, Radiance RGBE, OpenEXR, Integrated RAW converter plus DCRAW for direct import of virtually all digital camera RAW formats. The supported export image formats are : Radiance RGBE, OpenEXR, TIFF, PNG, PPM, BMP and JPEG. There are four windows that you can view: display of menu with images and adjustments, preview area, progress and navigator. When you choose to align the images, the application automatically compensates for any 'slight' camera wobble. Once the images are aligned, you may manually adjust to create a slight misalignment for image creativity (sometimes a slight misalignment can create a better HDR image by giving it more depth). It provides two tone-mapping options: 'Simplex' – adjusting histogram, gamma and saturation,  and 'Receptor', which is identical, but with the added bonus of compression and brightness. Personally, I work on 'Receptor' because it gives the greater effect if needed. Please delve into the 'Preferences', rather than work with the applications defaults, as this will acquaint you with the settings, allow you to specify your own final-image format, and select a destination file for your finished images. An excellent program.

Essential HDR Community Edition is a fantastic free HDR software that blows the others out of the water when it comes to tone mapping.  Their goal is to better Photomatix, which has made itself the bench mark of HDR software.  It has an easy interface that allows you to manipulate the image by tone mapping, histogram and color balance.  The best way to get a good result really is by using a tripod, however, it does have the ability for alignment if you have hand held the photograph.  Don't hold your breath here, I have found its not that brilliant.  Yes it is FREE, but the limitations of this software allows a maximum image size of 1mb.  To give you an example I took 3 images on different EV values 2592 x 1944 px (5 MP, 4:3).  After combing the images the results were:
.tiff gave me a size 858 x 647 px – 2,187.9 KB
.jpg gave me a size 858 x 647 px – 842.9 KB
Obviously to get the most out of it is to save as TIFF, it's enough for use on the internet or a decent A5 image.  For this reason its not my top choice.  You also have to remove the small watermark at the bottom of the image, not a lot to spoil it.

Result image can be saved in the following formats

    * Jpeg: 8-bit per channel RGB
    * BMP: 8-bit per channel RGB
    * PNG: 8-bit per channel RGB
    * TIFF: 8-bit and 16-bit per channel RGB
    * Radiance HDR

Source image can be in the following formats

    * Jpeg: 8-bit per channel RGB
    * BMP: 8-bit per channel RGB
    * GIF: 8-bit per channel RGB
    * PNG: 8-bit per channel RGB
    * TIFF: 16-bit per channel linear RGB
    * Canon Raw file, *.CRW and *.CR2
    * Nikon Raw file, *.NEF
    * Pentax Raw file, *.PEF
    * Sony-Minolta Raw file, *.ARW and *.MRW
    * Adobe DNG
    * Radiance HDR
    * OpenEXR

    Operating Systems: Linux, Windows and Mac OS X