Prepare for OCR

POST /api/document-prepare-for-ocr2 quota units per call · cache hits free

Prepare a document scan for OCR: deskew, binarize, denoise, contrast-stretch. Improves recognition rates on noisy phone-camera captures and skewed scans.

Cleans up a document image so the OCR engine has the best possible chance. Apply this before `document-ocr` for noisy inputs — phone-camera captures, photographed receipts, faxed pages. The pipeline is: - Deskew (auto-detect rotation up to ±15° and straighten). - Convert to greyscale. - Adaptive threshold to clean black-on-white binary. - Despeckle (remove isolated stray pixels). Output is a PNG ready to feed straight into `document-ocr`.

Inputs

Name	Type	Default	Description
image*	file	—	Input document image.
deskew	boolean	true	Rotate to correct skew.
maxAngle	number (0…90)	15	Cap on detected skew magnitude (degrees).
thresholdMode	enum (otsu \| adaptive)	"otsu"	Binarisation strategy.
denoise	boolean	true	Light Gaussian blur before threshold.

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	`25 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 invoice example.

# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/ocr-fixtures/document-small.png
IMAGE=$(base64 -w0 < document-small.png)

curl -X POST https://api.xtract.bot/api/document-prepare-for-ocr \
  -H "Content-Type: application/json" \
  -H "Accept: application/octet-stream" \
  -H "X-Account-Id: $XTRACT_ACCOUNT_ID" \
  -H "X-Api-Key: $XTRACT_API_KEY" \
  -d '{
  "image": "'"$IMAGE"'"
}'