HDR tips

A photographer sent me an email, “Ferrell, I am enjoying reading your book on HDR photography.  I have a Nikon D700 and thought perhaps that it might be possible to take one photo and the bracketing take place in the camera using the menus. Thanks in advance. Paul Fretts

Hi Paul,
A common approach among new HDR enthusiasts is to take a single image and in post processing create an over and under exposed image, save each one, then follow with HDR processing. This approach is incorrect. It’s not possible to create more dynamic range than the sensor captured simply by adjusting exposure in-camera or in post processing. The dynamic range of a single image is limited by what the camera sensor accurately records. To illustrate this, let’s say your sensor captured a single image with blown highlights. Those blown pixels are void of accurate data, you cannot recover the blown pixel data by doing an exposure adjustment of that image. Sure the mid-tones will get respond nicely to the adjustment but the bad ones are gone bye bye.
You may say, “What if I don’t have blown pixels and my shadow detail is good, then why can’t I use the exposure adjustment idea on a single image, save each image, then process to HDR?”  You can, but I’d argue that HDR-style processing is not needed, you’ve already captured the dynamic range of the scene in a single image, you can tone map that image if you like.

Two important scene indicators of High Dynamic Range.

The Sun – Compose any landscape or cityscape image with the sun in the scene and you’ll have High Dynamic Range. Start thinking in terms of 7 or 9 images at 1EV spacing.

Cave Effect – The cave effect is created when sunlight is blocked from all directions except the one you are looking. Of course the severity of the cave effect will vary based on it’s depth and overall % of the composed scene it occupies. The important thing is to be aware that you are dealing with High Dynamic Range and take 5,7,9 images at 1EV spacing. Here are a few examples: Store front where the interior is visible, tunnel entrances, the local vegetable/fruit stand, natural cave openings, and underside of a bridge with lots of I beams. You get the idea, take a moment and try to think of a few yourself.

The HDR knowledge base tells us that dynamic range can be as high as 1,000,000,000:1

That’s 1 billion to one and what does it mean? It’s simply the difference in EV from the center of the sun’s disc on a clear clear day to the darkest cave you can imagine, a place where there are no photons of light.

Is it common in nature? Nope, due to so much diffused light.

Should I worry about it? Nope, unless your a scientist taking measurements. It’s widely accepted in photography that the disc of the sun and surrounding area can be overexposed. But watch those clouds.

I often see posts that say “tone mapping a single image is not true HDR.”

Our primary goal as a photographer is not to capture HDR image sets with little thought about the scene. But through scene awareness we should concentrate on capturing the FULL dynamic range of the scene. It may take 3, 5, 7, or 9 images OR it may take just 1 image.

Single image tone mapping is not an inferior technique to the full blown HDR process when the single image captures the full dynamic range.

So where is the going? Process the full image set to HDR but also try to process a single image in the set. Choose the image based on the histograms and what areas of the image are important. I like to take 5 images at 1EV spacing so I have more options to chose from. There is one thing for sure, when you tone map a single image, ghosting and alignment issues will never be a problem.