Sobel Y
The vertical-gradient half of the Sobel–Feldman operator, introduced around 1968. It measures brightness change from top to bottom, so it highlights horizontal edges such as horizons, tabletops and eyelids, and pairs with Sobel X for full edge strength.
Spot it
- 01Horizontal edges glow bright
- 02Mid-gray flat regions
- 03Vertical edges vanish
Why it happens
Convolves the image with a 3x3 kernel that differences the top and bottom rows while smoothing horizontally with 1-2-1 weights, approximating the vertical derivative of brightness.
Recreate it in Pixio
Image edit prompt“Render this image as a Sobel Y gradient map: flat areas become neutral mid-gray, while horizontal edges appear as bright white above and dark black below, like an embossed relief lit from the top. Vertical edges almost disappear. Grayscale only, slightly grainy. Keep the original subject and composition recognizable.”