Tuesday, March 20, 2018

DigPhotog: Exposure and Histograms (W11-P1) Sp18

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 defined in a similar way.  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 photograph 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 on both iOS and Android is called PicsPlay.  Get the free version first.

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