How to Expand Dynamic Range
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by Rico Pfirstinger
It appears like two thirds of our X-PERT CORNER readers wanted to know more about dynamic range (DR) expansion. So here we go! Does the following scenario sound familiar? You take a picture of a landscape that looks wonderfully beautiful to the naked eye, only to find out later that the blue sky no longer looks blue and the fascinating cloud formations are just white blobs. The reason for this and similar disappointments is that the scene captured in the image has a larger dynamic range than your camera.
Every camera sensor is capable of capturing only a certain range of luminance—that is, a limited range between the brightest and the darkest parts of an image. The X-Pro1/X-E1’s range covers about 9.5 f-stops or exposure values. In other words, there are 9.5 EV between the minimum amount of light required for the sensor to depict something more than black pixels and the maximum quantity of light beyond which the sensor registers white pixels. This is the dynamic range of the camera. Within this range, the X-Pro1 or X-E1 can depict levels of brightness between pure black and pure white.
“Hardware” solutions
Unfortunately the world doesn’t abide by these limits, and many subjects exhibit a larger dynamic range than the camera is capable of capturing. We see these limitations, for example, in backlit situations and when people are standing in the shadow of an entrance. Professional photographers (and film directors) reduce the dynamic range of their subjects by using additional light. That’s why you’ll see an entire arsenal of floodlights and reflectors on large film sets even on bright days.
Only the luckiest photographers have the luxury of elaborate lighting equipment. Most of us have to make do with natural lighting, which often produces contrast in our subjects that exceeds a range of 9.5 EV. When you try to photograph these subjects with your X-Pro1, your images will either have blown-out white areas or blocked-up shadows, regardless of the combination of aperture and shutter speed you use. They may even have both! Contrasts that the human eye (or more accurately, the human brain) seems to process without any trouble pose near-impossible challenges for even the best cameras.
Then again, even a setup with studio lighting can involve plenty of dynamic range, that’s why I shot the following SOOC (= straight out of camera w/o further post-processing) JPEG in February 2012 in Warsaw using the DR Auto function of my pre-production X-Pro1. The camera chose DR400% and preserved the highlights of the skin (which was illuminated by daylight coming through a train window on the right). Click on the image for a high-res version:
But let’s get back to hardware: You can also use a graduated neutral density (ND) filter to decrease the dynamic range of a scene, typically a landscape. The top half of such a filter is dark and the bottom half is clear. The dark area is placed over a scene’s high-intensity region, such as the sky. Though this doesn’t increase the fixed dynamic range available in the sensor, it stretches usable dynamic range in practice.
Or you could use a camera with an EXR sensor, like the X10 or the X-S1. Then again, interest in getting to know more about EXR appears to be lackluster, as the number of votes for an “EXR Special” of this column is still ranking below 1000. Maybe this will change over the weekend? Here’s the poll, again:
Loading ...The following SOOC JPEGs from my X10 were taken in South Africa and show how EXR cameras can handle subjects with plenty of DR (click on the images for high-res versions):
