What is a RGB histogram, and what does it tell me?
A histogram tells you about the image’s exposure. Each vertical bar represents the relative number of pixels at that intensity value. Dark images have most pixels on the left side of the histogram, and bright images have most pixels toward the right. By reading the histogram, you can tell whether the image is over or underexposed, or if the scene exceeds the dynamic range of your camera. For example, if the rightmost bar in the histogram is very tall, many of the pixels are at maximum brightness, telling you that the highlights (bright portions) of the image are blown out. Adjusting the exposure to a faster shutter speed or smaller aperture will bring the pixels on the right toward the middle of the histogram, which means there will be detail in the bright areas of the image. For more information, take a look at this more comprehensive tutorial on histograms. PocketLoupe shows the individual color channels in the histogram, allowing you to see the exposure for the red, green and blue c
