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Tuesday, January 5, 2010

A Brief Guide To HDR Photography

High-dynamic-range photography has caught on like wildfire, and now with DSLRs capable of creating HDR images automatically, it’s time to revisit this hot trend

This Article Features Photo Zoom

Tone Mapping
Tone mapping is the process of converting the tonal values of an image from high to low. For an HDR image with a contrast ratio of 100,000:1, it will be converted down to have tonal values from 1 to 255. To do this, go to the HDR menu, Tone Mapping. A new window will open, and you should now see something a little more normal-looking (Figure 5a). There are lots of options for tone mapping, so I’ll walk you through them (Figure 5b).

Strength. This controls the strength of the contrast enhancements, both locally and globally.

Color Saturation. This controls the saturation of color in the image. I wouldn’t use this adjustment to create a black-and-white HDR image.

Light Smoothing. This controls smoothing of light throughout the image. I always leave this on high. If you set it to low, you can have halos around objects, and the image may look unusual.

Luminosity. This controls the compression of the tonal range, which has the effect of adjusting the global luminosity level. Basically, a positive value increases shadow detail and brightens the image. A negative value gives a more natural feel to the image.

Below these options is a box with four tabs: Tone, Color, Micro and Shadows/Highlights adjustments.

Tone Adjustments. The White Point and Black Point control the clipping of those luminance values. Moving them to the right clips the image, making the image more contrasted. Gamma adjusts the midtone of the image, making the image brighter or darker.

Color Adjustments. Temperature is similar to white balance. Moving it to the right makes the image warmer and to the left makes it colder. This can be useful for sunset images. Sometimes Photomatix will create images that are too warm to the point of looking wrong. Saturation Highlights and Saturation Shadows adjust the color saturation relative to the color saturation slider.

Micro Adjustments. Micro-contrast sets the level of accentuation of local details. This can appear to make the image a little more contrasted. Micro-smoothing smoothes out the local detail enhancements. This can reduce noise and produce a more natural-looking image.

Shadows/Highlights Adjustments. Highlights Smoothing reduces the contrast enhancements in the highlights. This is useful to prevent highlights turning gray and can reduce halos around objects. Shadows Smoothing reduces the contrast enhancements in the shadows. Shadows Clipping controls the clipping of the shadows, handy for reducing noise in dark areas of an image taken in low light.

The following settings are pretty much my favorites: Strength—75%; Color Saturation—60%; Light Smoothing—very high; Luminosity—+5; White Point—set to 10; Black—set to 3.35; Gamma—set to 0.85; Temperature—set to 0 unless it looks off and then adjusted to correct color issues; Micro-contrast—0; Micro smoothing—+2; Highlights Smoothing—0; Shadows Smoothing—0; Shadows Clipping—0. That, for me, is a nice image (Figure 6). I would then open it in Lightroom and tweak some more.


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