Exposure, Brightness, and Curves

Exposure, Brightness, and Curves

Exposure is the overall brightness of your image, determined by the combination of aperture, shutter speed, and ISO. In editing, the exposure slider adjusts the overall brightness by shifting the entire tonal range up or down. It is the most basic adjustment you can make. But exposure alone does not give you fine control over how different brightness areas of the image look. That is where curves come in.

The curves tool is a graph with input brightness on the horizontal axis and output brightness on the vertical axis. The default is a straight diagonal line, meaning input equals output. When you add a point to the line and pull it up, that range of tones becomes brighter. Pull it down, and it becomes darker. By adding multiple points, you can shape the curve to adjust shadows, midtones, and highlights independently. This is far more powerful than a simple brightness slider.

An S-curve is the classic adjustment for adding contrast. You add a point in the shadows and pull it down slightly. You add another point in the highlights and pull it up slightly. The dark areas become darker, the bright areas become brighter, and the midtones stay roughly the same. The result is more pop and definition without making the image look over-processed. A reverse S-curve reduces contrast by lifting shadows and lowering highlights, which creates a softer, flatter look.

The brightness slider in most editing software works differently from the exposure slider. Exposure adjusts the raw file's tonal values as if you had changed the camera settings. Brightness adjusts the midtones while trying to preserve the shadows and highlights. If your image is generally well-exposed but feels a bit dark, the brightness slider is often a better choice than exposure because it keeps your highlights from clipping and your shadows from blocking up.

A practical curves workflow starts with setting the black and white points. Find the darkest part of the image that should be pure black and the brightest part that should be pure white, and adjust the endpoints of the curve accordingly. Then shape the midtones for the desired contrast and mood. Finally, use the individual color channel curves to add any color grading. Working in this order gives you a clean, controlled result.