High Dynamic Range Images

dsc_1194-h3e_wA few days ago, I got another interesting kind of photo software from MacPhun: Aurora HDR

HDR stands for High Dynamic Range. Before I start a review of this new software, I want to explain the basics in this concept first.

Dynamic is the variance from brightest to darkest parts of a natural scene, which is visible lossless when looking on it or capturing it in a single frame. Comparing the capabilities of the human eye and a modern digital sensor, you’ll find a huge difference. According to (Source), the human eye (although not the best in nature!) has a dynamic range of about 20 f-stops (out of 23 – a range from starlight lit scenes to white snow in full high standing sun at noon without clouds in the sky). So, you can see details in the dark, even when the surrounding scene is very bright – or vice vera. The sensor of your camera has a dynamic range of 6 – 8 f-stops in jpg files (depending on the quality of your camera). In raw files you’re able to capture dynamic ranges of about 10 – 12 f-stops (also depending of the quality of your camera) . Why jpg-files are so bad and why you should use raw files instead, was the topic for a past post.

But back to our todays topic: HDR. To cope with the reduced dynamic range compared to our natural experience through our own eyes someone invented a technique to capture more information for an image. Therefore you have to take more than one shot of a scene by using several shots of an identical frame, but modify the exposure slightly by shifting the exposure time without changing anything else. You take one correct exposed shot balanced for the mid-tones. Next, you take an under-exposed image (i.e. -1 f-stop) and next an over-exposed image (i.e. +1 f-stop). The under-exposed image represents the highlights, so you should be able to see all the details in the bright partes of the image. In this image all dark parts might be black, but that’s fine for now. The over-exposed image is the opposite of the under-exposed image. Here, you get the details in the dark parts, while the bright parts are blown out and nearly white.

Don’t try to simply adjust your aperture, by changing the f-stop. Although, this results in a modified exposure-time, it also changes the characteristics of the image: the field of depth is changed, while the exposure balance stays the same 😦 That’s not our intention!

You have to use the “+/-“-key on your camera or switch to manual mode, to dial in the corresponding exposure times manually. Keep in mind, +1 f-stop means doubling the exposure time twice (.i.e. 1/100s -> 1/50 -> 1/25s) and -1 f-stop means dividing the time in halves twice  (i.e. 10s -> 5s -> 2.5s).

Just in case, the +/- 1 f-stop images aren’t enough to bring back details in the dark and / or bright parts, try +/- 2 f-stops or come up with a row of five more images (-2, -1, 0, +1, +2). You could also end up with even more than 5 image for a single series. Expand the series as long as you have any black or white parts in you image. Many cameras assist you in here, while marking these parts blinking (the mode is called ‘highlights’ in my camera menu and works only on the small screen on the back of my camera – the image is ok, only the in-camera playback is marked this way). By using this, you can shift the EV in each direction, as long as all of the blinking parts vanish in that direction. I.e. you increase +EV to get the dark details, but in the same moment, you’ll loose more and more highlights. As I said above, that’s ok. Next you increase your series -EV to capture the details in the highlights, by loosing the darks. That’s also ok. You have to increase +EV as long, as there are no blinking dark parts left and you increase -EV as long, as there are no blinking highlights left. You don’t need to increase in thirds, as your camera might step up and down. It’s enough to use the whole numbers as I mentioned earlier. As you might imagine, all of these requires an unchanged camera position! Always use a tripod for this and disable your image stabilizer while the camera is mounted on top of a tripod!

Back at home, take your series of images (usually 3 or more), make your usual corrections (i.e. shifting the horizon) for all images of that series exactly the same way and pay attention to get correct aligned images at this stage. All of them should show exactly the same cutting and the same orientation, convert them to tiff (for preserving all information – never use jpg in this stage) and use a HDR software, just like Aurora HDR from MacPhun (there are more software products available for creating HDR images) to fuse these files to a single balanced image with details in all parts of the image. Croping should be done at the very last step on the final image! And, that’s the point where I’m continuing soon!

For now, I’ve assembled a small gallery of some of my HDR images. Although, there are some photographers out there, who love very intense colors for their HDR images, I don’t do so! I use this technique very mild to get natural looking images.

Take care!

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3 thoughts on “High Dynamic Range Images

    • yes, they are different from our ‘normal’ experience. A friend of mine took several photos at night of a moonlit scene. He used an extreme long exposure time. And, although I knew the area, and the image was colorful, it was amazingly different – kind of strange. it’s a world of its own. Hidden for our eyes.

  1. Pingback: A new kid in the block: Aurora HDR | MyBlog - solaner

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