more HDR

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Grayscale photo of the engineering underpass. Slowly I'm getting bits of information about high dynamic range (HDR) images. Sometimes they're about Photoshop, sometimes about the camera, and sometimes I just get an overall confidence boost from the added practice. An article in Technology Review last week on new high contrast HDR displays gave me some info and raised more questions. (Take home from the article- if you're thinking of buying a high def display...hold off for a little while and high def HDR will be out.)

In the article I read that most of the current market for HDR is in the gaming industry. They use a lot of HDR video exported as 32bit per channel renderings from 3D applications. I also just learned that Adobe After Effects v.7 has the capability of editing this type of video. You can adjust lighting way beyond what you used to think was possible. But what would be our immediate gain in using the technology?

If you do a Flickr search on the tag "HDR" you get a lot of images. I'm impressed by the technology and a few of the images, but find many that seem pretty tacky. Most of the work is color- and it tends to be over saturated, flat, with unnatural contrast. It could easily appear on black velvet, or in a cedar frame with a light behind it and a waterfall that actually moves.

Merge to HDR Photoshop panel.The problem, I think, lies in the fact that there are quite a few choices to be made when you save the final JPEG for flickr, and very few people have the skill or sensitivity (as yet) to make the best choices. After selecting the images that you want to merge, they all open in the Merge to HDR panel. You can turn separate images off or on, choose final bit depth, and tweek an exposure "white point preview" slider. Clicking "okay" opens the final HDR file in a normal Photoshop window, except for a small slider in the window's lower bar that lets you continue to adjust lighting. There are a few commands available in 32 bit mode- Levels, Exposure, and Hue/Saturation for instance. The final conversion to an 8 bit (or 16 bit) image brings up more controls and more choices. With these tools, folks are making the kitsch.

Cattail as 32 bit and 8 bit.A benefit could be in the control: the continuing options after images have been shot. It would allow someone of limited camera skills to grab visual data that could be, essentially, reconstructed later. I tried to project some sort of scenario where I might recommend HDR techniques to a faculty member. A botanist, for instance, may use digital photos to make field notes. Bracketing the images, or shooting a variety of images at different film speeds, could help guarantee usable results under varying light- and skill- conditions. Deep woods shadow, bright meadow sun. No photography skills. Like using old-school curves, layer masks and channel opps, the expertise would need to exist for post processing.

Sassafras as 32 bit and 8 bit.I shot a series of plant images, as I thought a botany professor might. I did very little post processing, pretty much just what was required to get images on the web. The few plant shots shown here are double images, with the HDR merged group preview on the left and a single image from the group on the right. The image on the left, the HDR image, exists as a 32 bit per channel image that seems to be very tolerant of adjustment. The image on the right still exists as a 16 bit per channel RAW file, so is still somewhat adjustable, but I'm still assessing which is best.

Jewelweed as 32 bit and 8 bit.As in other HDR sessions, it 's obvious that a tripod and cable release are a necessity. In these HDR examples, particularly the cattail, you can see multiple leaf edges as the result of Photoshop trying to align leaves that were blowing gently in the wind. There is an "Allow Photoshop to align these images" option, which I leave on, but with some movement alignment is impossible. Also in the cattail HDR image you can see the sky is burned badly, where it isn't in the single version. That's a result of my including an overly bright image in my merge. The effect can be reduced greatly but not eliminated- so image selection, and ballpark correctness, are important.

If you want to open a 32 bit HDR, you can grab a cropped version of the jewelweed zipped here. Or, merge your own from these four cattail JPEG files or these five underpass shots.

Pen and ink sketch of the engineering underpass.
As an aside, after I shot the grayscale hdr above,I remembered this old sketch and pulled it out of a stack. I did it shortly after I moved to the area, summer of '79 or '80. I've done pastels of this scene, pencil sketches, watercolors, and taken lots of photos. I love to walk it. It's intriguing- the light effects are interesting, the architecture , too- but a motif is most often selected for the psychological impact on the artist. The subliminal implications of the visuals. I'll leave the Jungian symbolism to others; the need for academics to turn images into words has always troubled me.

1 Comments

dave, continued... said:

There's a common technique in Photoshop that involves using the same multiple exposures shot for HDR. Typically, one of the darker images would be opened in Photoshop, with successive versions dragged into place on separate layers; the best overall exposure on the top. All the layers are aligned, then areas of each are selectively masked until the top image shows throughout the entire view the best exposure and detail from each layer.

The development of adjustment layers with layer masks gave the process a boost. For my simple brain, this long-hand style process is much more intuitive, and much more controllable. To get an idea, open an image in Photoshop, and command/control click on a Channel palette icon- that gives you a selection of the brightest areas of that channel, with masking increasing as darkness increases. With that selection active, open a Curves adjustment layer and instantly you're targeting very specific information. Or, if the image is in a stack of layers, hit "delete" instead of opening an adjustment layer- that deletes the burned out areas allowing detail from a darker under-layer to show through. It sounds complex, but it really is pretty straight forward.

This is, though, just an approximation of natural luminance. But that's exactly what the jpeg saved from an HDR file is, too.I'm still at a point "skill-wise" where I'm getting much better results with the old method. Development of HDR displays, and new skills, may change that. I'm not sure which method would be easier to teach someone else.

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