This is a blog about my teaching, research and service with some occasional personal comments thrown in.
These are my notes on a variety of topics. If you want to follow my blog posts on a specific topic, then see the Table of Contents in the right-hand column. While I try to work in the realm of facts, logic and moral absolutes, if there are any opinions expressed here, they are my own. -WilliamHartPhD
Monday, October 21, 2013
DigPhotog: Exposure and Histograms (U7-P3) Fa13
In the field of statistics, a histogram is "a graphical representation of the distribution of data." The histogram below shows the distribution of black cherry trees according to height. Note that there are many trees between 70 and 80 inches tall and a few that are 60-65 inches tall and even fewer that are 85-90 inches tall.
Graphic credit: Mwtoews. Used under Creative Commons
In the field of photography, a histogram is similar, it is a graphical representation of data. But, what data?
A histogram for a photograph is "a graphical representation of the tonal distribution in a digital image. It plots the number of pixels for each tonal value." The tones in a photography range from shadows (the darker areas or pixels) to midtones (grey areas or pixels) to highlights (the white or bright areas of the photograph).
A photograph which is underexposed, for example, would have lots of shadow.
For visuals and further discussion see the videos below.
A key question: How could you use a histogram to determine if your photos have proper exposure?
A good app for showing the histogram all both iOS and Android is called PicsPlay. Get the free version first.
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