Smart crop (gradient)

POST /api/image-smart-crop-traditional2 quota units per call · cache hits free

Crop an image to a target aspect ratio while keeping the region with the most edge energy in frame. Uses a Sobel-gradient saliency map plus a sliding-window energy search.

Crops the input to a target aspect ratio, choosing the crop window that contains the most visual interest. Algorithm: 1. Sobel gradient on a downsampled luminance buffer → saliency. 2. Slide every legal window of the target aspect across the image and sum the saliency inside it. 3. Pick the window with the highest sum; apply it to the original-resolution image. Cheap, deterministic, and predictable — good fit for batch thumbnail generation where you want "focus on the busy bit" but don't want an ML model in the loop. For face-priority crop use `image-face-crop`; for ML-saliency crop see the upcoming `image-smart-crop-saliency` (T2, ONNX U²-Net). `aspect` accepts either a numeric ratio (e.g. `1.0`, `1.778`) or a colon-separated pair (`16:9`, `4:5`). If both `aspect` and explicit `targetWidth`/`targetHeight` are given the explicit dimensions win.

Inputs

Name	Type	Default	Description
image*	file	—	Input image bytes.
aspect	string	"1:1"	Target aspect ratio. Either `W:H` (e.g. `16:9`) or a decimal (`1.778`).
targetWidth	number (1…8192)	—	Optional explicit output width. When set, the crop matches this exactly.
targetHeight	number (1…8192)	—	Optional explicit output height. When set, the crop matches this exactly.
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	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 square 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-smart-crop-traditional \
  -H "Content-Type: application/json" \
  -H "Accept: application/octet-stream" \
  -H "X-Account-Id: $XTRACT_ACCOUNT_ID" \
  -H "X-Api-Key: $XTRACT_API_KEY" \
  -d '{
  "aspect": "1:1",
  "format": "jpeg",
  "image": "'"$IMAGE"'"
}'