What Brightness, Contrast, and Saturation Actually Change
These three adjustments each modify a different aspect of an image's pixel values, and understanding the distinction helps you reach for the right one. Brightness shifts every pixel's value up or down uniformly — a flat, global offset. Contrast stretches or compresses the range between the darkest and lightest values in the image, making shadows deeper and highlights brighter (or the opposite) without necessarily changing the overall average brightness. Saturation adjusts color intensity specifically, pushing colors toward vivid (high saturation) or toward grayscale (zero saturation), while leaving the underlying brightness/lightness of each pixel largely unchanged.
This is why "brightening" a washed-out photo by increasing brightness alone often looks worse, not better — a photo that looks washed out is frequently a contrast problem (values clustered too close together) rather than a brightness problem (values too low overall), and increasing contrast instead of brightness usually produces the more natural-looking correction.
Blur, unlike the other three, operates spatially rather than on individual pixel values — it averages each pixel with its neighbors, which is why it reduces fine detail and noise but can't be "undone" by any of the other three adjustments, since the detail lost in blurring isn't recoverable by shifting brightness, contrast, or saturation afterward.