That flat mountain photo is lying to you, and your brain is happy to go along. Depth there is not carved by geometry but by a quiet stack of visual heuristics baked into the visual cortex. Instead of waiting for binocular disparity or motion parallax, the system grabs color gradients, contrast falloff and aerial haze and treats them as non‑negotiable evidence of distance.
The bold trick is contrast. Near ridges keep higher spatial frequency and stronger local contrast, so primary visual cortex and later V2 neurons fire as if edges are closer in physical space. Far peaks fade into low‑contrast blobs, and that simple luminance gradient gets misread as a depth map. Then color joins the scam. Foreground rocks skew warmer and more saturated, while distant snow drifts toward desaturated blue; the brain, tuned by atmospheric scattering, tags that blue shift as "far away" without any conscious check.
Most persuasive of all is haze. Light scattered in the air creates veiling luminance that washes distant contours, and mid‑level areas like V4 treat this aerial perspective as a stable prior, not a suggestion. One faint mist layer across a valley and the scene snaps into a tiered relief in your head. No extra pixels. No stereo. Just a flat sensor image, plus a visual system that would rather invent solid mountains than admit it is staring at ink on paper.
