Overlay images

POST /api/image-overlay2 quota units per call · cache hits free

Overlay one image on top of another at a chosen position. Supports alpha transparency, configurable blend mode and opacity.

Composites a foreground image on top of a background image at the specified position. Inputs: - `background` / `foreground`: the two images. - `x` / `y` (default 0): pixel offset of the foreground's top-left. - `opacity` (default 1.0): foreground opacity multiplier. - `blend`: composition mode. `over` (default), `multiply`, `screen`, `overlay`, etc. Useful for adding logos, watermarks, or composing shots in design pipelines.

Inputs

Name	Type	Default	Description
image*	file	—	Background image bytes.
foreground*	file	—	Foreground image bytes.
gravity	enum (north \| south \| east \| west \| northeast \| northwest \| southeast \| southwest \| center)	"center"	Anchor for the foreground.
opacity	number (0…100)	100	Foreground opacity (percent).
scale	number (0…100)	0	Foreground scale relative to background's smaller side (0 = native).
offsetX	number (-8192…8192)	0	Horizontal offset in pixels.
offsetY	number (-8192…8192)	0	Vertical offset in pixels.
format	enum (png \| jpeg \| webp)	—	Output format. Defaults to the background's format.

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	2 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	`25 MiB`
Timeout	15s 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 red-ovr example.

# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/image-align/sample.png
IMAGE=$(base64 -w0 < sample.png)
# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/image-overlay/foreground.png
FOREGROUND=$(base64 -w0 < foreground.png)

curl -X POST https://api.xtract.bot/api/image-overlay \
  -H "Content-Type: application/json" \
  -H "Accept: application/octet-stream" \
  -H "X-Account-Id: $XTRACT_ACCOUNT_ID" \
  -H "X-Api-Key: $XTRACT_API_KEY" \
  -d '{
  "gravity": "center",
  "opacity": 1,
  "image": "'"$IMAGE"'",
  "foreground": "'"$FOREGROUND"'"
}'