Wednesday, December 26, 2007

Tame HDR to Produce More Realistic Images


For about a year now I’ve been bracketing exposure on most shots so I have the option of using high dynamic range (HDR) software to increase highlight and shadow detail in my shots.

As noted in this article at NatureScapes.net, digital cameras can capture a range of about 8 stops of light, while film cameras cover about eleven, and your eye covers 14, while an actual outdoor scene may cover 17. HDR software can help you restore some of that range of light and color that your film camera could capture, or that your eye might see.

Many people are now experimenting with or using HDR software, but it can be difficult to produce natural-looking results. By now the majority of my images on this site have some degree of HDR postprocessing involved. In the interest of timely posting, many are first pass edits that I'm not fully satisfied with or done fien tuning yet, but you can decide for yourself whether or not I'm on the right track and my experience might offer some value for you.

Here are some techniques and tricks I've learned to better control my HDR results in an attempt to produce more natural results. I consider this to be a list of basic to intermediate tips. I'm working on a list of more advanced advice on tips and tradeoffs to consider when handling some of your more challenging shooting and postprocessing situations.

Shoot RAW and work only from file formats that preserve maximum tonality data
- Compared to JPEG which has 8 bits of color information, my RAW files have 12 bits, and the extra 4 bits provide 16X more shades of each primary color. In simple terms the HDR software works with 4096 levels of each color instead of 256. The difference can be very noticeable in the results, especially in areas with subtle shading such as blue sky and orange sunsets. Working with JPEG files frankly produced crappy results for many of my shots. Some new cameras just starting to ship now produce RAW files with 14 bit color depth, so the HDR software will have over 8000 levels of each primary color to work with in RAW files instead of 256 in JPEG.

Consider your brightest and darkest shots from any HDR sequence. Using JPEG you're settling for 256 color shades instead of 4096 in 12 bit RAW, dramatically reducing subtle shades by a factor of 16X in exactly those darkest and lightest areas that you're trying to salvage. Assuming 2 stop spacing of shots, perhaps the results where I've noticed a clear difference occurred with colors and brightness values occurring in the 4 ev stops beyond all of the other exposures (the more detailed color data two stops above and two stops below all other shots, no matter what total range you're covering).

- RAW also enables you to change the white balance setting. Want to better preserve the color in your sunset? If your first HDR run on a shot reduces the color too much, try running HDR processing again using the shade or cloudy white balance setting for a warmer (more orange/yellow) tone. You don’t have that option, and can’t achieve the same results, working from JPEG files.

- As noted by the NatureScapes.net article:
Further, the camera applies a tone curve, compressing shadow tones in order to favor highlights. Since I personally find that shadow tones contribute a lot to my HDR work, I would not like to sacrifice them. Finally, introducing JPEG compression artifacts (however slight) into the HDR process may degrade image quality.
I understand there are arguments in favor of shooting JPEG. Typically the benefits raised are to get more continuous frames, more storage capacity, and potentially minimize subsequent workflow effort in RAW conversion. However, in my opinion, these factors are not particularly relevant for HDR work, especially landscape photography as discussed here.


- If you ever intend to "go pro" and submit to stock photography agencies, you'll be happy that you saved the original 16 bit TIFF output from your HDR runs (retaining your full 12 or 14 bit RAW quality, further expanded via HDR into the 16 bit TIFF color space), and don't have to re-run HDR interactively on thousands of archived RAW files to retain value from your shots. (I'm not talking about "microstock" agencies, which are fine with you spending hours to produce and manage high quality JPEG images that can be sold for pennies for online work.)

Use a Tripod and Use Auto Exposure Bracketing
- The less you touch your camera, the more likely your shots will overlay well and produce a sharp image. HDR software such as Photomatix may have the functionality to attempt to get misaligned shots to register well, but don’t count on it; it seems almost as likely to further misalign your shots. Having the camera take the shots as fast as possible also reduces any movement within the scene (leaves, clouds, etc.) that might turn into distracting ghost images in the result... better to prevent the problem and spend any postprocessing time doing something creative rather than trying to repair or salvage a shot with motion artifacts.

Use Interactive Mode, not Batch
- The default settings for Photomatix software for example seem to desaturate and overexpose many images and leave them with unrealistic halos of light around dark objects. HDR processing can reduce noise in some cases, enhance it in others. If you care about the quality of your results, all of these challenges are best faced in interactive mode.

Tame Halos: Set Light Smoothing to High or Very High
- This is your #1 tool to fight distracting light halos that may flag your results as HDR output, what some people might refer to as "overcooked." I set it "very high" at first, then back off a notch or two to see how much HDR the scene can handle.

Tame Noise: Adjust Micro Smoothing
- On some sequences HDR can cancel out noise, for others it might interpret severe noise as valid data and enhance it! Increase the Micro Smoothing setting to smooth out HDR-enhanced noise.

Restore Color: Postprocess in Photoshop or Photoshop Elements
- Since your HDR software shifted light intensities and color tones, something as simple as Auto Contrast and/or Auto Color Correction can make a lot of difference when trying to restore natural-looking lighting and color. Noise reduction can be needed too.

Restore a Natural Look: Layer and Blend HDR Result with a Single Exposure
- Sometimes my best results with HDR software are not acceptable, but neither are my results trying my best to balance the exposure and color in one of my single exposures for the same shot. Consider blending both your best single edit in with your HDR result! The single edit will most likely have better color and shading and the HDR result will have more shadow and highlight detail. A 50/50 or 60/40 blend may still not be a perfect result, but it may be better than either of the two results before you blended them!

I'd be curious to know what other techniques people have found useful, specifically when their intention is to create realistic-looking results.

If you decide to buy Photomatix, you can get a 15% discount by using the coupon code JeffSullivan when you by it from its publisher HDRsoft: http://www.hdrsoft.com/order.php

(I'm still tuning the focus of this site. If you like my inclusion of experience and technique tips in this blog, drop me a line to let me know in my guestbook. Thanks!)

Monday, November 26, 2007

Up In Smoke

My first attempt at editing a couple of smoke shots together, using layers and basic Photoshop Elements tools like dodge, burn, eraser.

To get this result I shot incense smoke from about 3 feet away. I used an external flash mounted on my camera (head rotated to mainly bounced off a wall to the side), manually set f/8 and 1/200 sec. (ISO 100), and had a dark background (black $2 disposable table cloth from a party store) a few feet behind.

I then edited a couple of shots together, using layers and basic Photoshop Elements tools like dodge, burn, eraser. The blue was in the smoke but I saturated it.

For more examples and technique ideas such as false coloring and mirroring, see: www.flickr.com/groups/artsmoke/

Wednesday, November 14, 2007

Night Photography with Meetup.com Photographers

Here are a few photos from tonight's outing with the Northern California Photography group, which organizes frequent outings through Meetup.com.

I used my Canon's Auto Exposure Bracketing function to take exposures darker and lighter than the automatic exposure recommendation, and I adjusted that recommended center exposure darker to reduce overexposure of the neon signs. I found that one to two stops underexposure seemed to produce the best results.

To spice things up a bit I decided to try some special effects. I had such good interesting results with zoom blur that I stuck with that for the evening. My best results seemed to be at ISO 100, f/16 or f/22, yielding an automatic exposure (after exposure compensation to make it a stop or two darker than the default camera recommendation) of 2 to 8 seconds, giving me plenty of time to make a slow, smooth zoom. For these shots I eventually tightened the bracketing to its small increments of 1/3 to 2/3 of one stop, not really doing much with exposure, just ensuring that I had multiple attempts at a given shot so I would have one with a smooth zoom and minimal vibration.

For night "cityscape" photos I processed my exposure bracketed files with Photomatix HDR (High Dynamic Range) software to extend the limited dynamic range of my digital camera and get better shadow and hightlight detail. Next time I want to use light sources (spotlight, flash), and try some handheld shots.

To get yourself out shooting more often, in a variety of environments and under a variety of conditions, in a productive learning environment sharing ideas and tips with other photographers, I highly recommend that you look into local groups through Meetup.com!

Saturday, November 03, 2007

Fall Trip 2: Return via the Eastern Sierra

With a flat tire resulting from hours of driving on washboard dirt roads in Death Valley, I decided to spend the night close to the town of Biskop in the BLM campground aptly named "The Pit."

The Pit is a former gravel pit. Now that it's a campground, it's still basically just a gravel pit... with the addition of a pit toilet. The price? $2, entirely appropriate for a pit. Fortunately there's a county park nearby with a pond, so it's a short drive to nicer dawn vistas.

Dawn sun lights the Eastern Sierra on the way home from Death Valley.

Smoke mixes with morning mist over Crowley Lake alongside the Eastern Sierra range in California.

Friday, November 02, 2007

Fall Trip 2: More Death Valley

The Racetrack in Death Valley National Park is an amazing place. In seasons of high rainfall, the lake bed at The Racetrack becomes covered by a shallow depth of water, and a layer of slippery clay fills the cracks in the surface. Scientists speculate that if the surface of the water freezes and the wind blows hard enough, large sheets of ice with rocks stuck down through them can "sail" across the flat surface, moving the rocks and making trails in the mud as they pass.

One example that scientists' theories regarding rock movement at The Racetrack in Death Valley don't seem to explain is when rocks seem to take equal but opposite paths, such as these two paths here.

One of the first intersting shot opportunities is to catch the sunlight as it first reaches the mountains to the West.

The shadows move quickly across the surface of the playa at The Racetrack in Death Valley, but if you get just ahead of them you have a few seconds to set up your shot before the next rock and its track straddle the boundary between darkness and light. As the sun rose and the shadows retreated, I jogged from rock to rock and from shot to shot along the shadow boundary and ended up about a mile away from where I started!

To capture the detail and texture of the cracked mud surface of the playa, this shot was taken with a 10mm wide angle lens (16mm equivalent) about 16" off the ground, capturing the ground below out to the horizon (at the lens' smallest aperture of f/22 for depth of field of course).

As I chased mountain shadows into the middle of the Racetrack playa I encountered a very large rock, probably weighing 300-400 pounds, which had made its way via wind, mud and ice over the past 3000 years out to the middle of the dry lake bed. It was large enough to make a good subject in a wide angle shot that embraced the clouds forming overhead around the moon.

Next I headed further northward to Eureka Dunes... note the size of the hikers on the mound towards the upper right! Upon reaching the town of Big Pine a couple of hours later, I intended to buy gas then head up to the Ancient Bristlecone Pine Forest for sunset light. Unfortunately I had a flat tire, my second failure of a Goodyear tire in three weeks due to driving on washboard dirt roads.

Thursday, November 01, 2007

Fall Trip 2: Zion National Park to Death Valley

When you reach the "standard" dawn shooting spot in Zion National Park a little early, you might as well capture a star trail shot. If the moon is up as it was for this shot, you can capture color in the surrounding trees and landscape as well.

As the sun lights the surrounding peaks, a graduated neutral density filter can be useful, but additional software or darkroom postprocessing may be warranted.

With light reaching the bottom of the canyon so slowly in Zion, it is fairly straightforward to head up the valley and find places to catch the advancing light in reflections in the Virgin River. A late morning departure from Zion leaves enough time to reach Death Valley by sunset.

The vast salt plain near Devil's Golf Course is one good option for dusk shots.

If you're really ambitious you can continue on another couple of hours on rough dirt roads to reach The Racetrack. Many people destroy a tire or two on the trip (as I did twice in my last 2 weeks on dirt roads, including here). This shot is one exposure, catching a spotlight shining into the air, then shining it on me standing as it I were still holding the spotlight... done twice.

For this single exposure shot I simply walked backwards holding a flashlight, then stood still as a spotlight was briefly flashed on me.