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Downtown Lens: High Dynamic Range (HDR) Part 3 -- Processing

By Dave Bullock
Published: Thursday, September 25, 2008, at 12:18PM

What your eye sees is not always what your camera captures. Your camera’s dynamic range, the level of tones it can capture, is much narrower than what nature presents.

High Dynamic Range photography allows you to capture a view that more closely mimics real life. The real magic happens not in the camera, but in the computer.

In the first installment of this series, I talked about the camera and tripod you will need to create HDR images. In the second installment I went over the core of the process, capturing multiple images. In this final installment I will discuss bringing it all together and processing it in software.

There are a number of different software applications on the market which allow you to process individual images and create an HDR image. Personally I really like the results from HDRSoft's PhotoMatix. Its batch processing capabilities and wide range of features give it a leading edge over the competition.

Go ahead and download a demo version of PhotoMatix so you can give it a try. The demo is fully functional, but watermarks the company's logo on your image. If you decide you want to start using it, the software costs $99. I bought it a long time ago and I'm glad I did. HDRSoft has included full version updates for free so far.

Once you have the software downloaded and installed, run it and click on the button that says "Generate HDR image". This will open a dialog box that will let you browse for your images. Use the dialog box to select three of the bracketed images you took during the last installment. These should be three images of the same subject, one properly exposed, one underexposed and one overexposed.

Once you select them and hit OK, you will see a screen with many options. If you used a good tripod, you won't need to align the images, but feel free to leave this turned on. Further down there is an option to "Attempt to reduce ghosting artifacts" which will try and get rid of things that moved in between your exposures like cars or people. I have had limited success with this feature.

If you are using RAW files, which you should be doing, you won't have the option to adjust tone curve. There are also options to change white balance, I normally just choose "As Shot", but if you know the color temperature of the light your subject was under you may want to adjust this. Finally you can adjust what color gamut your files are, I shoot everything in AdobeRGB as it has a wider gamut than sRGB. This is a setting in your camera, so set it to whatever you have in your camera. When in doubt pick sRGB.

Once you have the settings down, click OK. Photomatix will then convert your images into one HDR file. It will take a few minutes depending on your processor speed. After this image is generated it will pop up on the screen. You will note that it doesn't look very good. This is because your monitor can not display HDR images as its dynamic range is too narrow. If you scroll your mouse over the image you will see that there is really a very large amount of detail which will be shown in the HDR viewer window. If you don't see this window click View > Show HDR Viewer.

Because we want to be able to see and print the whole tonal range of this image, we will have to map the HDR photo to levels our monitor and printer can display. This is called Tone Mapping. Click the Tone Mapping button to proceed.

A new dialog box will pop up with a huge array of options. PhotoMatix has a good preview system, so try changing the parameters to get a result you like. The strength slider has what is probably the most noticeable affect on the final image and can make a photo look either very realistic or surreal and cartoonish. When you are happy with your settings click "Process". This will also take a few minutes. When it is done click File > Save and save the image as a JPG or TIFF.

There you go! You are now on your way to becoming and HDR master. Now you just have to get out and shoot more photos to process. Have fun and happy shooting!

This post is the eighth part in a weekly series entitled Downtown Lens in which I will discuss a photograph and the technique that relates to it.

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