Posts Tagged ‘HDRI’

Yesterday was hot and fairly humid. Today, it was more of both. Basically, hair was on instant frizz. The winds out of the south to southwest, depending on the time. The wind was more like a hair dryer though.

In the morning, before all was too humid, my daughter and I were able to shoot some video covering how to shoot HDR images on a Nikon D7000. The sunshine made viewing the screen on the D7000 difficult, but moving to the shade for the setup solved that. I also learned that the flip does not focus, so getting too close was a problem. Oh well, live and learn. Will put the video together with the images and move forward.

Vacation is basically half over. Now it is time to start moving wake-ups back toward where they need to be come next week.

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In continuing the discussion about HDRI, attention is turned toward the two dark images that were chosen for the final product. Remember, these articles are not being written from well documented notes, but from the files in the auto-generated file name from PhotoMatix.

The base photo is heavily shifted to highlights, so more details need to be picked for the shadows. The outer two photos in the next two levels of bracketing (±1⅓ and ±2) provide this. The details for these photos are given. Remember, the base photo had EV at -⅓ due to overexposure tendencies of the camera and lens.

DSC_0034f/22, 1/4 sec, 48mm, EV -1⅔

DSC_0037f/22, 1/6 sec, 48mm, EV -2⅓

The next step will involve using the software to put it all together. Tone mapping is best started at a low end and moved toward more saturated.

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HDR what?

High dynamic range imaging. It’s all the rage these days. Typical digit photos capture more information than can be displayed on the limited color scope of 32bit screens. The exposure settings also further limit the range a photograph contains. It is not possible for the camera to capture high level of details in the shadows and the light simultaneously.

Enter High Dynamic Range Imaging.

The concept is quite simple. Take several photos of the same subject at different exposures, bracketing above and below the balanced shot, combine them in layers using a computer and then either balance them for tone or detail. The mapping, especially of tone, is a subjective matter, but the aimed result is to have an image that show details in the shadows and the highlights.

Searching the web for these images brings an interesting array of artistic visions. Some choose to so blowout colors that the pictures look really fake and old. A more subtle approach brings something closer to what the eye might see, only better.

But what about IBL?

Confusing the matter is computer 3D rendering and the concept of Image Based Lighting. This concept uses an image to simulate lighting for a scene. The image is typically an HDR image and the uninitiated tend to think of HDR or HDRI as the lighting concept. It isn’t. HDRI is just a tool used for IBL.

Ok, back to the photography stream.

Though there is no requirement on the number of photos to use to layer, the best results lend themselves from 5 images taken at ⅔ EV steps, the middle image being the effective 0 EV. This is not as subjective a statement as it may seem. In most photographic situations, having images at ±⅔ intervals gives the algorithms their best information for extrapolation. Intervals smaller can lead to too much being picked up in one area. Intervals larger leave too much of a gap.

Over the next several posts, I’ll cover how to create HDR images, making full use of the auto-bracketing features found on most DSLR cameras. I’ll also cover gotchas such as subject movement and depth of field changes. Buckle in and hand on, it will be a fun ride.


Clifton Gorge, Yellow Springs, Ohio – 26 May 2008

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