HDR Photography: Adjust Tone Mapping in Photoshop
After you have tone-mapped your high dynamic range image in Photoshop, you can make adjustments, such as using Exposure and Gamma to protect highlights, using Highlight Compression to squeeze the highlights to fit, equalizing the histogram, or adjusting the Radius and Threshold to achieve better contrast and sharpness.
Tone Mapping: Exposure and Gamma
Choose Exposure and Gamma from the Method drop-down list in the HDR Conversion dialog box.
The key with adjusting the Exposure and Gamma sliders is to lower the Exposure setting so you don’t have any blown highlights, and then adjust the Gamma setting to get at the right lightness (which can affect contrast). It might not look like a good photo at this point — you’ll have to rely on more editing after tone mapping.
In this image, the clouds were on the verge of blowing out until the Exposure was reduced. It wasn’t necessary to change the Gamma. Contrast can be enhanced later in editing through Levels or Curves adjustments.
Tone Mapping: Highlight Compression
Choose Highlight Compression from the Method drop-down list in the HDR Conversion dialog box. This figure shows the selection in the dialog box and the effect on the image. In this case, Highlight Compression does a good job of saving the clouds.
Tone Mapping: Equalize Histogram
Choose Equalize Histogram from the Method drop-down list in the HDR Conversion dialog box. The figure shows the result of equalizing the histogram. In this case, contrast is enhanced, but details are lost in dark areas of the building and in the clouds.
Choose Local Adaptation from the Method drop-down list in the HDR Conversion dialog box. Working with the Local Adaptation settings allows you to control the two sliders (Radius and Threshold) as well as alter the histogram. Begin by working on the histogram.
When you hover your mouse over the image, as shown in this figure, the cursor becomes the Eye Dropper tool. Click to see the tone under the Eye Dropper appear on the histogram as a hollow diamond. This lets you sample specific tonal regions and gauge whether to change the histogram for that area.
With that out of the way, see whether a combination of changing the Radius and Threshold settings from the default improves the image. In this figure, the Radius was increased to emphasize local contrast and the Threshold was decreased to avoid smoothing it over. The result is a bit sharper than the original with good contrast.