In editing software such as Photoshop or Lightroom, what is the graph that represents the distribution of light called?

• A. Histogram
• B. Curves
• C. Levels
• D. Luminosity

Answer: (A)

The histogram is the graph that shows how light is distributed across an image. It plots the number of pixels at each brightness level, from dark on the left to light on the right. The height or value at each point tells you how many pixels share that brightness. This makes it a direct read on exposure and tonal balance: a histogram piled up toward the left means many dark pixels (underexposure), toward the right means many bright pixels (possible clipping of highlights). Spikes at the far left or far right indicate crushed shadows or blown-out highlights.

In Photoshop or Lightroom you’ll see the histogram in the panels where tonal adjustments are made, and you can view histograms for individual color channels to spot color casts. Curves and Levels are adjustment tools that manipulate tones; Curves maps input to output with a curve, while Levels uses the histogram to set black/white points and midtone gamma. The graph that shows the actual distribution of light across the image, though, is the histogram. Luminosity refers to brightness in a perceptual sense or to a channel, not to the graph itself.