Image stitch

POST /api/image-stitch4 quota units per call · cache hits free

Stitch two overlapping images into one panorama using ORB keypoint matching, RANSAC homography, and a warp-and-composite step. No SIFT / patent-encumbered features required.

Combines two overlapping images into a single panorama: 1. ORB keypoints + binary descriptors on both inputs. 2. RANSAC homography mapping `right` onto `left`'s frame. 3. Compute the union bounding box of both projected canvases. 4. Warp `right` into the output canvas; paint `left` on top. Useful for: - Quick two-shot panoramas without spinning up a heavy pipeline. - Combining overlapping document scans. - Joining before/after frames into a single image. Multi-image (>2) panoramas can be stitched by calling this tool iteratively (stitch(A,B) → result; stitch(result, C) → …). Native N-image support would need the full Stitcher module from OpenCV contrib, which isn't currently compiled into our build — see ADR-0004 (build size budget). When the two images share too little overlap (or none), the homography fit fails and the tool returns 422 with `code: no-homography` so callers can branch cleanly.

Inputs

Name	Type	Default	Description
left*	file	—	Left / reference image. The output canvas is built around this one's frame.
right*	file	—	Right / source image. Warped to align with `left`.
nfeatures	number (200…8000)	2000	ORB keypoint cap. Higher = slower + more robust.
matchRatio	number (0.05…1)	0.25	Fraction of best-distance matches kept for the homography fit.
format	enum (png \| jpeg)	"jpeg"	Output image format. PNG keeps the transparent border where `right` didn't reach; JPEG fills it with black.

Response

Modes: binary, stream, json. Cache: yes (24h TTL).

Large outputs stream: responses over the 4 MiB cache limit are piped through as they are produced instead of buffered. They carry x-cache-skip: size and are never cached — identical follow-up calls recompute.

Every response carries x-cache (HIT / MISS / BYPASS), x-cache-signature (stable across identical inputs), and the rate-limit headers listed below.

Quota & limits

Cost per call	4 units against the 10,000-unit monthly quota. Cache hits are free — only cache misses decrement.
Burst limit	200 requests per rolling minute, shared across all tools.
Max request size	`50 MiB` (base64 inflates file payloads ~33% — the limit applies to the decoded bytes).
Max response size	`50 MiB`
Timeout	25s wall clock.
Rate-limit headers	`X-RateLimit-Limit`, `X-RateLimit-Remaining`, `X-RateLimit-Burst-Limit` on every response; `X-Quota-Warning` once 80% of the monthly quota is spent; `Retry-After` on 429s.

Errors

Errors are JSON with an error string; schema failures add a details object (Zod's flattened field errors).

Status	When	Body
400	Input fails the tool's schema (wrong type, missing required field, malformed base64) or the file bytes can't be parsed as the expected format.	{ "error": "invalid inputs", "details": { "fieldErrors": { … } } }
401	Missing or invalid X-Api-Key / X-Account-Id headers (or no session when called from the browser).	{ "error": "unauthorized" }
404	Unknown tool id, or calling /api/* on the website hostname instead of api.xtract.bot.	{ "error": "not found" }
413	Request body over the tool's max request size, or an image header declaring more megapixels than the tool's pixel budget.	{ "error": "…exceeds maxRequestBytes…" }
415	Content-Type isn't application/json on the json-body transport.	{ "error": "unsupported content-type; expected application/json" }
429	Monthly quota or the 200/min burst limit exhausted. Check Retry-After and the X-RateLimit-* headers.	{ "error": "monthly quota exceeded", "monthRemaining": 0, … }
5xx	Conversion engine failure. Safe to retry; if it persists, the input is hitting a bug — please report it.	{ "error": "…" }

Code samples

Built from the self-overlap example.

# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/image-stitch/sample.png
LEFT=$(base64 -w0 < sample.png)
# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/image-stitch/sample.png
RIGHT=$(base64 -w0 < sample.png)

curl -X POST https://api.xtract.bot/api/image-stitch \
  -H "Content-Type: application/json" \
  -H "Accept: application/octet-stream" \
  -H "X-Account-Id: $XTRACT_ACCOUNT_ID" \
  -H "X-Api-Key: $XTRACT_API_KEY" \
  -d '{
  "nfeatures": 2000,
  "matchRatio": 0.25,
  "format": "jpeg",
  "left": "'"$LEFT"'",
  "right": "'"$RIGHT"'"
}'