Why Fisheye Cameras Are Needed
To cover 360° around the vehicle with four cameras, each needs a horizontal FOV near or beyond 180° — only fisheye lenses can do that. But fisheye imaging carries severe barrel distortion — straight lines become arcs — so distortion correction must come first.
A Four-Step Pipeline from Fisheye to Bird's-Eye View
1. Distortion Correction
A per-pixel mapping is built from the fisheye optical model (equidistant / equisolid projection) to "straighten" the curved image back to normal perspective.
2. Camera Calibration
Cameras shoot calibration patterns in a standard environment to solve each camera's intrinsics (focal length, distortion coefficients) and extrinsics (position and angle relative to the vehicle body). Calibration accuracy directly determines stitching misalignment — one session in a garage stays valid for the vehicle's life.
3. View Transform (IPM)
Using the extrinsics, each corrected image is projected via Inverse Perspective Mapping (IPM) onto a roof-centered bird's-eye plane, where the four views naturally align around the vehicle.
4. Stitching & Blending
Adjacent cameras' fields overlap; the overlap bands need luminance balancing and seam blending to avoid brightness discontinuities and "ghosting".
Three Easily Overlooked Keys
- Exposure/white-balance sync: if the four cameras expose independently, the picture splits into uneven quadrants. A unified AE strategy keeps the whole image consistent
- Frame sync: the vehicle is moving — all four channels must be captured at the same instant, or stitching edges smear
- Dynamic guidelines: reading the steering-angle signal, the rear-wheel trajectory is computed in real time and overlaid, swinging with the steering while reversing
What Are 3D View and 540°?
3D mode drapes the bird's-eye view over a rotatable 3D vehicle model for free-angle inspection of any side; 540° adds a streaming rearview channel on top of the four-camera surround view, removing C-pillar, rear-headrest and cargo obstruction for full "front-rear-left-right + direct rear" vision.
TSIMSAFE is one of the drafting organizations of China's surround-view national standard; 360°/540° products have been installed on over 1 million vehicles. See the 360° surround-view solution or aftermarket surround products.
