A histogram is a handy tool that provides information about the distribution of colors in an image, in other words, displays its tonal range. The image tones can range from pure black on the left edge to pure white on the right edge of the histogram. So, what you have to pay attention to if you want to learn how to read a color histogram is the shape of the graph and where the peaks of the graph are.
Put simply, the higher the graph is at a given point, the more of a certain tone there is in an image. Therefore, considerably dark images with lower exposure and a lot of shadows will have a graph that peaks on the left side, while brighter images will have a histogram that is higher on the right side.
Tap in the toolbar.
If the histogram isn't visible, scroll down the list of adjustments and tap Customize.
Select Histogram in the list of color adjustments to turn it on. To hide the histogram, deselect it in the list of color adjustments.