The Perfect Sunrise

by NULLZ

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I took one shot of oil lamps. Partial metering mode was used and I focused on the bright yellow light, as expected the image was captured with only the light and its immediate surroundings visible.

enter image description here

But when I was fiddling around in Lightroom and increased Exposure, I noticed that I could see all the objects that were there in background. How is that possible ?

Edited in Light room, increased exposure by 5 stops.

enter image description here

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2 Answers

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.jpggrey

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.

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When you view a RAW image, what you are actually seeing is a conversion of a RAW image. This is true whether you are looking at it on the screen on the back of your camera or on your computer screen, because the screens themselves are not designed to display more than an 8 bit per color dynamic range. Your camera, depending on model, probably records RAW files in either 12 or 14 bits per color. The designer of the software (or firmware in the case of the camera) that is displaying the image made some assumptions based on an "average" image and this default conversion is applied to the RAW image when it is displayed. Just as it is the case that information is discarded when you convert a RAW image to JPEG, the image as it is displayed on the screen does not include all of the information contained in the RAW file.

When you start fiddling around in Lightroom you are replacing the default instructions applied in camera or on initial display in Lightroom with instructions you have customized to that particular photo. By increasing the exposure four stops, you are telling the program to show the detail in the darker parts of the picture at the expense of the brightest parts of the picture. Notice how the detail in the flames themselves and their reflections on the holder has been washed out? Using tone mapping you could attempt to get some of that detail back by decreasing the level of the highlights without decreasing the overall brightness of the mid-tones and shadows as well. Tone mapping is used to help squeeze as much of the the information in a 14 bit RAW file as we can into an 8 bit JPEG.

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But this is a JPEG, so shouldnt all data been lost already ? –  GoodSp33d Feb 4 '13 at 7:49
    
With a JPEG you can still amplify the details in the shadows as well, just not to the same degree as with a RAW file. Boosting exposure of a RAW file is akin to "pushing" film when you develop the negative. Boosting exposure of a JPEG is akin to dodging (making lighter) the print you make from the negative. –  Michael Clark Feb 5 '13 at 9:33
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