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Learning Image Processing with OpenCV by Gloria Bueno García, Oscar Deniz Suarez, José Luis Espinosa Aranda, Jesus Salido Tercero, Ismael Serrano Gracia, Noelia Vállez Enano

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Histograms

Once the image has been defined with a data type and we are able to access its gray level values, that is, the pixels, we may want to obtain a probability density function of the different gray levels, which is called the histogram. The image histogram represents the frequency of occurrence of the various gray levels in the image. The histogram can be modeled so that the image may change its contrast levels. This is known as histogram equalization. Histogram modeling is a powerful technique for image enhancement by means of contrast variation. The equalization allows for image areas of lower contrast to gain a higher contrast. The following image shows you an example of an equalized image and its histogram:

An example of an equalized ...

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