AeroMark Images | Looking Inside HDR

Looking Inside HDR

January 15, 2017  •  Leave a Comment

In 2015 I showed an example of what is called high dynamic range, or HDR, photography. My example was the Boeing 747 that had served as the testbed for an airborne defensive system, the airborne laser. Today I'm moving the discussion from large, exterior, photography to small, interior, to see how HDR can have value there, too.

Above is the interior of an Embraer 300 shot on location at Scottsdale airport (KSDL) showing diagonal slices of the five separate images used to create a final. No single set of exposure settings on a camera could have captured clean detail in the full range of brightnesses, from the clouds in direct sunlight to the carpet under the seats, so I used HDR techniques to get the desired result.

Below are those five separate exposures — on the left, the clouds have full detail but the interior is completely black, while on the right the interior is a bit too bright (good for seeing under the seats) while the sky is just a featureless white glow. Each step, from left to right, represents a doubling of the amount of light admitted to the camera's sensor.

Embraer 300 interior HDR spread Fooling Our Eyes
The challenge is not just the camera, but the medium by which we view the image because, get this: the reality of the original scene has brightness levels that are about 19 doublings from lightest light to darkest dark. A computer screen is capable of showing only 10 such doublings. And the brightest paper with the best printing can show only 7! So how can we possibly represent reality?

We fake it.

With the goal of preparing a single image that appears to show the full range of brightness and detail, we use software to combine the five separate exposures into a single one that appears natural. The key word is "natural." We've all seen HDR images that look like this:

Embraer Phenom 300 cabin 20121110 HDR 00 overdone If this is the intended result, great. Typically it is not. This hyper effect is, essentially, the HDR process gone awry, but it can be instructive for our purposes.

What you see is the computer transitioning elements in the image from light to dark, as our eyes expect, but since neither the monitor nor a print can display the full range of brightness, it represents changes in brightness in discrete areas. For instance, in the above hyper image, the clouds go from dark to light (let's call it going from a brightness of 7 to 10, with the latter being pure white). Then the portion of the seat near the window goes from, maybe, 6 to 9. In reality the bright part of the seat is nowhere near as bright as even the darkest part of the clouds, but being separated in space allows our eyes go along with the deceit and we perceive it as realistic.

Thus, if we capture the proper set of different exposures and process the images, individually and then as an HDR group, we can create a final that looks real and natural. Like this:

Embraer Phenom 300 cabin 20121110 HDR 00x16 Details, Details
As with any marketing-level photography, details are important. For HDR the quality of the final image depends, in large part, on making the images consistently the same and different. Each frame must be shot from the same position — no movement of any kind, shot-to-shot — and with equal difference in terms of exposure — how much light enters the camera.

The former is best accomplished with a sturdy tripod that doesn't get jostled between shots. Make sure the legs are tightened at whatever length they are, their feet are firmly planted (be especially careful on carpeting or loose ground), that the camera is firmly attached to the tripod, and that triggering the shutter release doesn't cause camera or tripod to shift or tilt or wobble. A wired or wireless remote shutter release can help with this last dictum.

For exposure, the software that puts the disparate images together typically prefers equally spaced exposures, usually in 1-stop (a single doubling) increments. In my example, the five separate exposures are spaced like that which, combined with the camera's rated 13.1-stop (13+ doublings) dynamic range, yields 18+ doublings to effectively gather detail in all the relevant areas.

Next, the separate images should be processed carefully, to not over-improve each individual frame, and then loaded into software that specializes in the transformation from disparate images to unified whole. Adobe 
Photoshop has some built-in abilities, as does Adobe Lightroom. I use a plug-in for Photoshop from Nik Software called HDR Efex Pro 2, which I value for its ability to yield naturalistic results. Still, sometimes there's something about the images that comes out better when processed with Photomatix Pro from HDRsoft. Each of these can also produce a range of less-natural results, from subtle to outrageous and, of course, there are other apps out there, so you might research the web to find one that best suits your situation.

What Else?
I won't (continue to?) bore you with details, but the other important tip for shooting for HDR is to keep the aperture unchanging from shot to shot. This means your shutter speed will be the exposure factor that will vary and, depending on the light levels you encounter, this can lead to speeds that are longer than you're accustomed to, bringing more importance to the stability of your tripod/camera setup. (Changing the aperture from shot to shot would result in different portions of the scene being in or out of focus — not a good thing.)

If you're finding those long shutter speeds to be a problem, though, don't be tempted to increase the sensitivity, the ISO, of your camera when capturing the images. If you do, the resultant digital noise will end up emphasized by the HDR process, with sparkly results. It might be pretty, but it won't be what you're after. Unless it is…

Some subjects or situations present important opportunities for image making that are not also accompanied by ideal lighting. The above image could have been rendered in a single shot if artificial lighting had been brought into the aircraft, then configured and arranged to illuminate that interior in a naturalistic manner without damaging any of the furnishings, being unduly reflected in glossy surfaces, or appearing in-frame. So, time and money and risk. In this case, HDR was the right solution.


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