Image diff

POST /api/image-diff2 quota units per call · cache hits free

Visual diff between two PNGs. Returns the diff image (regions of change highlighted on a faded copy of the first input) plus a 0–1 similarity score and the count of differing pixels.

Compares two PNG images pixel-by-pixel and returns: - `diffPng`: a base64-encoded PNG showing changed pixels in bright red on a faded greyscale copy of the first input. - `diffPixels`: the count of pixels that differ. - `similarity`: `1 - diffPixels / totalPixels` (1.0 = identical). Tunable: - `threshold` (default 0.1): 0–1 colour-difference threshold. Smaller = more sensitive. - `ignoreAntialiasing` (default true): skip anti-aliased pixels. Useful when comparing the same UI rendered by different engines. Use cases: visual regression testing, A/B page-snapshot comparison, CI verification of generated thumbnails / OG images. Both images must have identical dimensions.

Inputs

Name	Type	Default	Description
imageA*	file	—	Reference / baseline PNG.
imageB*	file	—	Comparison PNG (must match imageA's dimensions).
threshold	number (0…1)	0.1	Colour-difference threshold. Smaller = more sensitive.
ignoreAntialiasing	boolean	true	Skip anti-aliased pixels when counting differences.

Response

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

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	`32 MiB` (base64 inflates file payloads ~33% — the limit applies to the decoded bytes).
Max response size	`32 MiB`
Timeout	30s 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 small-difference example.

# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/image-diff/sample-a.png
IMAGE_A=$(base64 -w0 < sample-a.png)
# Download or substitute the example input:
#   curl -O https://xtract.bot/examples/image-diff/sample-b.png
IMAGE_B=$(base64 -w0 < sample-b.png)

curl -X POST https://api.xtract.bot/api/image-diff \
  -H "Content-Type: application/json" \
  -H "Accept: application/json" \
  -H "X-Account-Id: $XTRACT_ACCOUNT_ID" \
  -H "X-Api-Key: $XTRACT_API_KEY" \
  -d '{
  "threshold": 0.1,
  "imageA": "'"$IMAGE_A"'",
  "imageB": "'"$IMAGE_B"'"
}'