Technology Corner

Why does Adobe keep putting 32-bit HDR in Photoshop?
Because it's the way of the future!

by Julio Palleiro

Do you know what an HDR image is? Do you even know what HDR stands for?
“High Definition… R-something”? You would be completely wrong. The letters HD have been thrown around a lot lately in the television and radio, however HDR has been around for a long time.

HDR means High Dynamic Range.

If you did not know this then stick around and read further.

Why should you know about HDR? If you are in the photographic or design industry, this will benefit you enormously.

The specifics of Dynamic Range require some knowledge of the photochemical processes or cinematography, so I will keep the explanation in layman’s terms.
The Dynamic Range in imaging refers to the range from the lightest to darkest light values. Okay, so that may seem pretty vague. Not really, if you chart out the white and the black points of a photograph and fill in the in between values, this is the dynamic range of an image. This chart is a histogram.

Now okay, that seems pretty obvious for most of you. So lets move on to ‘HIGH’ Dynamic Range and how to achieve that.

A camera can only capture a range of 5-8 light values or exposure values. A human eye, on the other hand, can see a range of 14. So simply put, High Dynamic Range imaging adds exposure value.

How to add EV?
This is way easier than you can imagine... Bracket exposures.


*Now this practice can only work if you are shooting with a tripod because the camera has to be 100% steady. *

Set the camera to capture 3 -5 exposures varying from 1/3, 2/3, 1 or 2 stops under and over. This means that you lock in your Aperture (f-stop) to your preference or light availability and the camera will automatically take 3 or 5 images (depending on your cameras options). One image will be properly exposed, one or two will be underexposed, and one or two will be overexposed. You know have a broader range.

But wait that’s 3-5 different images, how does that do me any good?
There are programs that combine the images into one flattened, 32-bit, HDR image. This is where the tripod comes in handy. If you tried this handheld, you cannot combine the images. You need 3-5 identically aligned images of different exposure value to accomplish this.
Okay, so now your still asking, “So what? Why do I need an image that has extra exposure value?”

During post-production, using an application such as Photoshop, you can now bring back all the details from the darkest and lightest points of the image(tutorial). This is an example of an image that we recently created here at Rich Imaging, Inc. (Photography courtesy of Rudolf Bekker).

Click here for large final image

Please be advised that this final image was retouched, so don’t think that creating an HDR image will magically convert five images into one finished product. The HDR process only creates more possibilities during post-production, it isn’t a short cut. The added light values allow for the retoucher to maximize every detail, every grain, and every pixel.

All it takes is a quick setting on the camera during your shoot.

For more examples of HDR imaging, click here and here.

And for a great read, here is the Bible of HDRI, the HDRI Handbook.

Thanks for sticking with me. I hope this has been helpful to you. Leave feedback.

Next time: IT’S FINALLY HERE! CS4, only 18 months after CS3. How did I survive for 18 months without CS4? Quite easily actually. Full review next time.

November 2008

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