In the most common form of histogram the independent variable is plotted along the horizontal axis and the dependent variable is plotted along the vertical axis. The height of any of the points on the graph indicates the number of pixels in that particular tone. A histogram is a bar graph that shows how frequently data occur within certain ranges or intervals.
It can be defined as a set of rectangles with bases along with the intervals between class boundaries and with areas proportional to frequencies in the corresponding classes.
It is a graph that shows the distribution of pixels in an image with the shadows are represented on the left the highlights on the right and the midtones in the middle. A bar graph where the data is represented in equal intervals. A feature of histograms is that they show the frequency of continuous data such as the number of trees at various heights. In the most common form of histogram the independent variable is plotted along the horizontal axis and the dependent variable is plotted along the vertical axis.