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# What Is a Histogram Test?

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• Written By: Maggie J. Hall
• Edited By: Susan Barwick
• Last Modified Date: 11 October 2019
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Histogram tests are linear graphs that visually depict the distribution of large amounts of data which provide an overall view of frequency and variability. Similar to bar graphs, histograms have sets of linear columns, but each column typically represents a class in the data distribution. Checking the continuity of analog to digital converter (ADC) signals, balancing photographic light exposure and color, and evaluating general statistical data are all uses of histograms.

The components of a histogram test generally include a title, the x and y-axes, and the bars representing the event, item, or object, and the legend. The horizontal x-axis typically displays bars, called classes, which are usually grouped tightly together. These class columns denote information gathered by quantitative measurements which may be expressed in quantities such as time, length of, or specific location. The vertical y-axis generally illustrates the histogram frequency distribution, or the frequency of occurrences in each class. Optional legends can briefly define or identify the classes.

The pictorial display of a histogram test shows a data summary without the need for lengthy textual explanations. Histogram analysis allows one to visualize the data and immediately obtain information regarding class comparisons and frequency of events. The information that histograms provide may measure overall performance or answer questions related to occurrence.

Electrical engineers commonly use a histogram test for determining factors related to ADC signals. The graphic display may be used to ensure the continuity of transitioning one signal to another or to illustrate interference and noise patterns within the signal. Technicians might also use histograms when analyzing optimal signal strength or signal strength in general over a measurable period of time.

Most digital cameras come equipped with a photography histogram that measures the light exposure and color gradients of a scene in real time. Each bar of the histogram test on the liquid crystal display (LCD) expresses the number of pixels exhibiting shadow traits or a specific color.The horizontal x-axis denotes the color gradient from black to white or red, green, and blue to white across the scene. Light exposure displays alert the photographer when a scene requires flash or additional external lighting. Single or triple color histograms indicate when a picture might require a color balance adjustment.

Seismologists use a histogram test for evaluating earthquake occurrences. Scientists recording tremor activity may compare size and frequency correlating with the cycles of the moon, number of occurrences at a specific fault line, or frequency of tremors at multiple locations around the world. Livestock specialists use histograms for analyzing herd productivity. Tests can also measure the fat content of meat and milk as well as the desired characteristics of fleece producing animals.