A Photoshop gradient map is different from placing a normal gradient across a document. It maps chosen colours to the brightness values already present in an image, which makes it useful for duotone artwork, cinematic colour grading, metallic colour treatments, poster graphics and controlled campaign palettes. Search phrases such as Photoshop gradient map, cinematic gradient, duotone gradient, chrome gradient, sunset gradient and gradient preset often describe a colour system rather than a background shape.
Start by deciding what should happen to shadows, midtones and highlights. Deep blue shadows with warm highlights can create a cinematic contrast, while a two-colour map can produce a clean duotone. Metallic looks usually need more colour stops because the visual impression comes from alternating dark, bright and mid-tone bands. The preview is a reference; the final stop positions should be adjusted for the photograph or artwork underneath.