19 May 2009

Exposing to the right

Exposing to the right is the technique of pushing histogram to the right side. Why use this technique?
Well - it is known that we can get the best results out of the digital image sensor if we use this technique. In old days (with film) photographers underexpose a little to get more saturated photo. If we underexpose in digital, we will expose noise in dark areas when we adjust shadows in postprocesing. Especially when using high ISO.
We won't find so much noise in bright areas. So all to do is keeping that our exposure will be bright - usually a little brighter than camera suggest.
But be careful - if we expose too much, we will get blowing highlights. This means that there will be no picture - it will be pure white (if we simplify a little for this example). So bride's dress won't have any great details from fashion designer, but we will find dress white - with no picture!
And we don't want that. We want that white dress will:
- be white
- have details.
To achieve this we can use technique exposing to the right. Photographer want to have histogram as far on the right (where the bright part of photo is) as he can - without going over the edge!

It is not so complicated. A sample how I use this technique.
I check if something blinks (overexposed highlight areas with no image information will blink). If answer is yes, then I decrease exposure so much, it just stops blinking. DONE.
If I see a bright area that's not blinking and there is enough room on the right of histogram. I increase exposure until it just touch right edge or maybe starts blinking, then go back off for minimum (on my camera 1/3 stop). DONE.

There are one exceptions not to use this role strictly. Sometimes there are very bright areas (usually small) and this areas aren't important. For example part of bright sky, lights in background ... This areas can go over right edge of histogram. Let them go - if the most important part of photo has good exposure. For example, if face and clothes has good exposure, then let goes lights over right edge. Put histogram in a way, that white shirt will be the most right point of (captured) histogram.

If you use RAW - and I highly recommend this - then you have some extra range where you can get detail even if photo is (little) overexposured.
You should also know that histogram (and photo) on back of your camera uses 8-bit jpeg. This means that camera uses some of algorithms - depends on your setting on camera (contrast, saturation ...). Test, test and test.

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