Why do dark background details appear when I raise exposure in Lightroom?
Asked 2/2/2013
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2 answers
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I photographed oil lamps using partial metering and focused on the bright flame. The original image looked like it contained only the lamp and a small bright area around it, with the rest appearing black. But when I increased Exposure in Lightroom by about 5 stops, objects in the background became visible. How can detail appear from areas that seemed completely dark in the original view?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
3
Two reasons:
Because we don't see linearly and our brightness resolution sucks. Look at a gradient in 8 bit (256 grey values):
http://www.tftcentral.co.uk/images/dell_2408wfp/gradient_grey.jpg
We see about 16 grey patches and the two ends are most compressed for us. It's not until value 30-50 we start seeing details. So a lot of objects can be hidden or even suppressed into this area by the initial raw processing, which leads me to the ...
Second reason:
The raw processor can suppress a lot of captured details in the low end for example to reduce the perception of noise. Since most cameras are 14bit nowadays, and you view the end result in 8bit, those 30 values in 8bit was more like 1920 values in the raw. Which means that you can take the perceived black part and create a good looking 8bit image without posterization - if it weren't too infected by noise.
Originally by user11455. Source · Licensed CC BY-SA 4.0
user11455
13y ago
0
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Because the detail was often captured in the RAW file even though the preview made it look black.
A camera sensor records much more tonal information than your screen can show. Many cameras save RAW data at 12- or 14-bit depth per channel, while most previews and displays show only about 8 bits per channel. The camera or RAW software creates a default preview that compresses tones and may push very dark values toward black, sometimes also hiding shadow detail to reduce the appearance of noise.
When you increase exposure in Lightroom, you are not creating detail from nothing—you are remapping faint recorded shadow values so they become visible. Human vision also does not perceive brightness linearly, so subtle dark differences can look completely black until they are lifted.
This works best with RAW files because they preserve much more shadow information than JPEGs. The tradeoff is that lifting shadows strongly can also reveal noise and reduce image quality.
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