By Joe Kashi, for the Redoubt Reporter
Achieving optimum results when using digital cameras at higher ISO settings requires careful post-processing tailored to the problems generally encountered under lowlight conditions, and that’s our topic this week.
When any image is exposed at higher ISO sensitivities, noise and degraded resolution become noticeable problems. Even high-grade zoom lenses, like the Olympus PRO series, are not at their best optically when used wide open, often necessary in dim light. Many of these problems can be largely corrected with later post-processing.
I first import all RAW image files directly into Adobe Lightroom so I have a basic reference point. I’ll then use Lightroom to identify the most promising images and delete files with uncorrectable problems, like serious motion blurring. When done, I’ll pre-process the remaining RAW files with DXO Optics Pro 10, the best lowlight, noise-reduction and optical correction software of which I’m aware, and then transfer the processed files from DXO back into Lightroom for fine-tuning.
DXO Optics Pro 10 tends to result in highlights that lose some tonal detail and so are slightly underexposed. That’s an advantage in lowlight work because the slightly underexposed file of any bracketed set is usually the file made with the shortest shutter speed, thus the least amount of potential motion blurring. DXO contains many automatic correction capabilities that make sense for automatically processing large quantities of low-grade typical images, such as poorly exposed family vacation snapshots, but exhibition-grade prints require a high degree of individualized correction, something that I’ve found easier with Adobe Lightroom.
For these reasons, I turn off all DXO Optics Pro 10 automatic corrections except for “Prime” noise reduction of RAW files, “chromatic aberration” and “purple fringing” correction, and “DXO lens softness” correction of RAW files. Likewise, I do not further sharpen images with DXO’s “unsharp mask” feature. Basically, I use DXO only to eliminate digital noise and optical flaws in the candidate images.
DXO can be set to export in bulk all processed files directly to Lightroom as separate DNG universal RAW-format files. Using Lightroom’s file comparison feature, you can then decide whether the original RAW file initially imported directly into Lightroom or the DXO-processed file better suits your concept.
Consider whether to correct any distortion caused by optical imperfections. This is best done initially with DXO’s automatically downloaded lens correction modules, but also can be done manually with Lightroom’s “Profile” correction feature. Experiment with the volume distortion corrections found in DXO and see which option looks best for each photograph.
When a camera and subject are tilted relative to each other, odd perspective results that may — and I emphasize “may” — look better if corrected to appear more rectilinear. To some extent, this can be accomplished with Lightroom’s manual perspective correction feature, but DXO’s optional Viewpoint 2 software is much more powerful. Be aware that any significant perspective corrections will result in loss of some border portions of an image. Crop and straighten any slightly off-kilter images as necessary.
Then make individualized corrections. I’ll first click Lightroom’s “Remove chromatic aberration” check box to ensure maximum removal of the color fringing typical in high-contrast situations. This is a no-lose correction and I don’t understand why Adobe has not made it a default action. Then, adjust to taste Lightroom’s clarity slider, which can improve apparent sharpness (“acuity”) by increasing the microcontrast between adjacent fine detail. Increasing clarity also tends to brighten shadow detail, something that may be important for lowlight photographs.
Next use Lightroom’s “Auto” exposure correction button found immediately above the exposure and contrast sliders. This works particularly well for underexposed RAW format image files made with high dynamic-range cameras such as we discussed last week.
The Auto exposure adjustment automatically sets many different exposure parameters and it’s helpful as an initial starting point, even though it tends to overexpose and brighten images too much. Using the exposure slider, reduce the “Auto”-adjusted exposure to taste, then other exposure settings such as highlight, white, shadow and black areas.
Images made in lowlight conditions tend to have some too-bright highlight areas that may require reducing overall highlight brightness, while shadow details may need to be boosted. I suggest first reducing or brightening highlight, shadow and black areas to taste. Lowlight images often look better when contrast is boosted. The “Auto” function will get your contrast setting within the approximate general range, but you’ll need to fine-tune the overall exposure settings.
Be careful that you have just the right amount of true black in lowlight photos. If very dark areas are not truly black, then they’ll often have dark mottled colors that may initially go unnoticed but look unnatural and unpleasant in a final print. If your blacks are not truly black, move the black slider toward the left, using Lightroom’s Develop module histogram to monitor these changes.
Lowlight images tend to take off-color casts. As a starting point, use Lightroom’s “WB” (white balance) feature found near the top of the Develop module. The “Auto” setting is a good basic starting point for further fine-tuning using the temp (blue-yellow) and tint (green-magenta) sliders. You can always backtrack and undo any Lightroom correction. Small changes here can make a very noticeable difference, so make these changes in small increments.
Now that you’ve made some overall corrections, it’s likely you’ll need to locally fine-tune some small areas. This is best done with the correction brush and graduated filter tools found just below the Develop Module’s histogram. Using these tools, you can make localized exposure, clarity and color balance corrections to specific parts of an image.
Where possible, I prefer to correct too-bright or too-dark areas using the correction brush set solely to correction of the specific problem. A highly specific adjustment to only one tonal range looks more natural and is less likely to clumsily bleed into adjacent areas. Fine-tuned processing like this is critical to optimum lowlight images because a large, overall correction may adversely affect other parts of the picture.
If you’re in the Homer area this Friday, stop by the opening reception for my new exhibit of lowlight photos, “Veiled Images,” and we can discuss the technical problems inherent to these demanding conditions. The free opening reception is at Kenai Peninsula College’s Kachemak Bay Campus from 4:30 to 6 p.m. Friday.
Local attorney Joe Kashi received degrees from MIT and his law degree from Georgetown University. He has published articles about computer technology, law practice and digital photography in national media since 1990. Many of his articles can be accessed through his website, http://www.kashilaw.com.