Compensating exposure after the shot is made.

Northern flicker (above) and Tree swallow (below).
I don't always get the shot I want every time I press the shutter.  Sometimes I just have the camera set up incorrectly.  Given the fact that there are so many available functions and situations are usually in constant flux, it is likely to use the right setup at the wrong place and time.  For example, when shooting in full sun using a manual exposure mode and then shooting in deep shadow without making changes will likely result in a severely underexposed image (top left).  In the reverse situation, shooting previously in a shaded area then switching to a sunny location without changing the settings will result in an overexposed photo (bottom left).  Both images are undesirable, but is it still possible to save the image?

Shooting in RAW mode gives much more latitude, literally, because the RAW image will capture a greater width of tonal values than what a JPEG will.  As a result, it is often possible to be off by a couple of stops and still end up with a viable result.  This is not to suggest that exposure values are unimportant.  I always like to bring the best image I can into post-processing, but that doesn't happen every time.  The photos on the left were taken with the exposure being severely off, the top one by about -2.5 stops (underexposed) and the bottom one by + 2.5 stops (overexposed).  To compensate in post for the top image I increased the exposure setting by a value of approximately 2.5 (making dark areas brighter).  I reduced exposure by about the same value in the bottom image.  So, what can we learn from this?

I could do a proper colour balance with the flicker but had a hard time with the swallows.  The white area was so overexposed that there was no detail present; there was no colour to lock onto.  The flicker had plenty of details in all of its colourings.  Look at the breast feathers of the swallows.  Notice that there is no detail there.  The tree swallow histogram (left) shows a shaft of white at the far right hand side.  That area has what we call blown out highlights.  The histogram of the flicker has coloured bars there instead of white; the exact colours can't be captured because the colour palate is out of range, but even in the brighter areas there are still details.

Here are some conclusions.  First of all, try to make the best exposure you can.  Secondly consider shooting in RAW mode as it can capture a wider range of exposure values and there is more room for error.  Lastly, if you are going to make an error of exposure, be on the underexposed side rather than the overexposed side.  Digital images have more latitude for darker values than brighter ones.  The opposite is true for film media.  Getting a good print from an overexposed negative is difficult, but not so much from an overexposed one.

Thanks for reading.   www.ericspix.com   Eric Svendsen






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