Crepuscular Rays - HDR

As mentioned in previous posts, I've been experimenting with stitched HDR images. A couple of weekends ago I was returning from a no-show sunrise at Stony Creek Backwash when the clouds split open revealing a Crepuscular Ray's over the city. Given the overcast sky and the bright rays of sunlight, there was no way I could correctly expose a single image:

crespuscular rays, stonycreek backwash - metered exposure

Recognisng the HDR image opportunity, I bracketed 9 shots at one stop intervals (-4, -3, -2, -1, 0, +1, +2, +3, +4) for each of the four frames in the sticth. Ideally I would have liked to bracket at 2 stop intervals but this is not possible with the D200. In the end I discarded all the images except for the -2, 0, +2 sequence. The next challenge was to tone map the image.

Using Michael Freeman's informative "Mastering HDR Photography" as a reference, I compared PhotoShop CS3's HDR functions with PhotoMatix and FDR tools. Although I admire much of the obviously HDR tone-mapped images that appear on Flickr, I was looking for a tool that gave me the most photo-realistic results. My other criteria for selecting a tool was usability. Of the three tools I found FDRTools the most intuitive program to use. I found PhotoShop's curves local tone mapping option to difficult to use and PhotoMatix' interface too complex. As it turned out after much experimentation, FDR tools also gave me the most photo-realistic results too.

crepuscular rays, stony creek backwash - hdr version

The workflow I followed for the image looked like this:

Capture

• Four frame stitched image @f11 - bracketed -4, -3, -2, -1, 0, +1, +2, +3, +4 (36 shots in total)

Pre-processing

1. Process raw images in PS Camera Raw (White Balance as shot) - save as Tiff files.
2. Tone map each of the four frames in FDR tools - Compressor 7, Contrast 5, Smoothing 2.
3. Stitch using AutoPano Pro - save as PSD file.

Post-processing

1. Set white point using Levels.
2. Additional tone mapping with Shadows/Highlight.
3. Modify yellow and green tones with Selective Color.
4. Apply a lighter curve to foreground, masking out the sky with a Quick Selection.
5. Apply an Unsharp Mask for the midtones - 20%, 120 radius, 0 threshold.

Although not totally happy with the end result - the image still looks obviously HDR - I am pleased that I spent the time experimenting with the process. For larger stitched images (22 frames), bracketing five-nine images per frame may not be practical. But for smaller images and where the light dictates it, I'm looking forward to applying the technique in New Zealand in a fortnights time.