White balance

POST /api/image-white-balance1 quota unit per call · cache hits free

Auto-correct the white balance of a photo. Uses the grey-world assumption — the average of all pixels should be grey — to neutralise colour casts from tungsten lighting, shade, or mixed sources.

Neutralises colour casts caused by lighting that wasn't fully white — incandescent bulbs, deep shade, overcast sky, mixed fluorescent tubes. The algorithm assumes the average pixel in a typical scene is grey; it computes each colour channel's mean, then scales every channel toward the overall mean so the new average is neutral grey. Useful for: - Quick auto-WB on phone snapshots before further editing. - Pre-processing photos for downstream colour analysis (OCR, product matching) where colour-cast distortion hurts results. The grey-world assumption breaks when the scene legitimately is dominated by one colour (a red wall, a green forest); in those cases the output will look over-corrected. For colour-managed photography use a dedicated grey-card workflow instead.

Inputs

Name	Type	Default	Description
image*	file	—	Input image bytes.
strength	number (0…1)	1	Blend factor between the original and the corrected image (0 = no change, 1 = fully corrected).
format	enum (png \| jpeg)	"jpeg"	Output image 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	1 unit 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 default example.

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

curl -X POST https://api.xtract.bot/api/image-white-balance \
  -H "Content-Type: application/json" \
  -H "Accept: application/octet-stream" \
  -H "X-Account-Id: $XTRACT_ACCOUNT_ID" \
  -H "X-Api-Key: $XTRACT_API_KEY" \
  -d '{
  "strength": 1,
  "format": "jpeg",
  "image": "'"$IMAGE"'"
}'