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New tech notes on my site
Aug 19, 2011 02:41:43   #
jchutchins Loc: Asheville, NC
 
Example without diagrams

http://www.jchutchins.com/Jchutchins/TechNotes/TechNotes.html



The camera histogram is a graph of a jpeg thumbnail that represents the maximum range of light values the camera can capture, in 256 steps. (0 equals Pure Black, and 255 equals Pure White) In the middle of the histogram are the mid-range values. The values from just above zero and just below 255 contain detail.





The left side of the histogram represents the maximum dark values that the camera can record. The right side represents the maximum white values the camera can capture. On either end (tails) of the histogram the values contain no detail. They are either completely black, or completely white.



The top of the histogram (peaks) represents the number of different colors, a value over which you have no control. To achieve a correct exposure we are mostly concerned with the left and right sides of the histogram.



We are especially concerned with the right side of the histogram, the images highlights. As illustrated above, when peaks butt up to the right side of the histogram, the highlights are blown out. or contain no detail -- they are pure white; conversely, when peaks butt against the left side of the image, the shadows are clipped, or contain no detail -- they are pure black.



Rule of Thumb

The generally accepted rule of thumb is to expose for the highlights, making sure they don’t tough the right edge of the histogram, but are as far to the right as possible and control the shadows in post processing.


Specular highlights are the exception (reflections from metal, glass, and water) these are true white areas.

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