Available on this page is a small set of images, each derived from the same high dynamic range source. The tone reproduction operators used here, are Photomatix (which I suspect most Flickr HDR afficionados are familiar with), as well as photographic tone reproduction. This is not a fully-fledged comparison of everything with everything. If you want that, I suggest that you check the literature. It is meant to demonstrate that lacing images with artifacts during the process of tone reproduction, which is giving HDR imaging a bad reputation, is unnecessary.
Photomatix Pro - Exposure Blending
Images 1 - 5 below are generated with the exposure blending facility available in Photomatix 3.0. This setting enables the best comparison with other techniques, because the number of parameters is strictly limited. The images below were generated with default settings, unless otherwise stated. Note the watermarks in these images: I have used the software for evaluation only, the results of which are presented here.
Photomatix Pro - Tone Mapping
The images tonemapped with Photomatix are created with the 'detail enhancement' operator. Parameters as stated below underneath each image (Images 6 - 8).
Greg Ward's Photosphere software allows high dynamic range images to be created, and then saved in either HDR or as a conventional eight-bit image (Image 9).
This images was created with my own little tool, which is based on sigmoidal compression. The paper was published in 2005 by IEEE Transactions on Visualization and Computer Graphics (Image 10).
Photographic tone reproduction comes in both local and global varieties. A local operator is more expensive to compute, and takes the local environment around each pixel into account. It gives better compression. The global operator is a sigmoidal function, executed per pixel. It is cheap to compute and gives good results for most images (Images 11 - 14).
Click on any image to start the slide-show.
The results are discussed below.
Comparison
1. Photomatix exposure blending, 'auto' option. No adjustable parameters.
2. Photomatix exposure blending, 'adjust' option. Default parameters.
3. Photomatix exposure blending, 'adjust' option. 'Strength' parameter set to +10.
4. Photomatix exposure blending, 'intensive' option. Default parameters.
5. Photomatix exposure blending, 'intensive' option. 'Strength' parameter set to +10.
6. Photomatix tone mapping, 'details enhancer'. Default parameters.
7. Photomatix tone mapping, 'details enhancement'. Parameters adjusted to emulate an image with artifacts as typically seen on the Flickr HDR groups
8. Photomatix tone mapping, 'details enhancement'. Parameters adjusted to produce an image with minimal artifacts.
9. Image produced with the Photosphere software. No adjustable parameters.
10. Image produced with the photoreceptor-based technique (published IEEE TVCG 2005).
11. Photographic tone reproduction. Local operator, default parameters (published SIGGRAPH 2002).
12. Photographic tone reproduction. Global operator, default parameters (published SIGGRAPH 2002).
13. Photographic tone reproduction. Global operator, key parameter set to 0.22 (published SIGGRAPH 2002)
14. Photographic tone reproduction. Global operator, key parameter set to 0.30 (published SIGGRAPH 2002).
Discussion
The purpose of presenting this set of images is to show what happens when certain choices regarding tone reproduction operator and parameter settings are made.
To begin, the simplest of the Photomatix algorithms, the 'auto' option available in the exposure blending tool, does a reasonable job avoiding halos (Image 1). There are no adjustable parameters (hence the name 'auto'!), so that what you see is what you get. In this case, the image ended up a little too dark, albeit not by much. This is probably the best image I managed to create with Photomatix.
The 'adjust' option in Photomatix' exposure blending tool allows three parameters to be adjusted, the most interesting of which is the 'strength' slider. Images 2 and 3 show that increasing this parameter makes the image a little lighter, but also starts to produce halos. Image 3 shows a lightening of the sky around the balloons, which should not be there.
Images 4 and 5 show the 'intensive' option in the exposure blending tool of Photomatix. Once more, the 'strength' parameter is the most useful. Here it allows the amount of detail to be adjusted. Both images show artifacts around the sun in the form of halos. In addition, the halo around the left balloon is much smaller than the ones created with the 'adjust' option. Image 5 is over-compressed, and shows an ugly smudge in the sky around the Photomatix watermark.
The Photomatix 'details enhancement' tone reproduction operator allows many parameters to be adjusted. Here, three versions are shown in Images 6, 7, and 8. The default parameters were used in image 6. Here, no specific artifacts are noticeable, but the image has come out a little too dark. The parameters for Image 7 were adjusted to highlight the potential for artifacts with the Photomatix software. The image is woefully over-compressed, with halos merging into random splodges. It is not unlike a large number of images posted on Flickr. It exhibits what some call the 'HDR look', and which I call a horrible set of unnecessary artifacts. It is highly unnatural and highlights the dangers of using Photomatix unless you know what you are doing. Please understand that HDR is not a style that you can either like or dislike. High dynamic range imaging has nothing to do with artistic freedom. What you see here is an artifact of the software that you choose to use, in combination with the parameters you choose to abuse.
Images 9 to 14 show several alternatives made with other software. Even here, the images vary somewhat in style. This is to be expected, given what is going on under the hood. However, each of these algorithms aim to produce a natural looking image, and to a large extent I think they succeed.
Once more, if you want a specific unnatural look, post-process them with whichever filter you like. Do not mistake high dynamic range imaging and tone mapping as techniques which should produce unnatural output. A good high dynamic range image is one that is taken in an environment where normal photography would break. It should be tonemapped to produce results that you would not immediately pick out as being different or funny. High dynamic range imaging is not meant to be glamorous.