SnapOtter/apps/docs/tools/image/compare.md

description

description
Compare two images side by side with pixel-level diff visualization and similarity score.

Image Compare

Upload two images to compute a pixel-level difference map and a numerical similarity percentage. The output is a diff image highlighting changed regions in red.

API Endpoint

POST /api/v1/tools/image/compare

Accepts multipart form data with two image files. No settings field is needed.

Parameters

This tool has no configurable parameters. Upload exactly two image files.

Field	Type	Required	Description
file (first)	file	Yes	The first image
file (second)	file	Yes	The second image

Example Request

curl -X POST http://localhost:1349/api/v1/tools/image/compare \
  -H "Authorization: Bearer si_your-api-key" \
  -F "file=@original.jpg" \
  -F "file=@modified.jpg"

Example Response

{
  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "similarity": 94.52,
  "dimensions": { "width": 1920, "height": 1080 },
  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/diff.png",
  "originalSize": 4900000,
  "processedSize": 280000
}

Response Fields

Field	Type	Description
jobId	string	Job identifier for downloading the diff image
similarity	number	Percentage similarity between the two images (0 to 100)
dimensions	object	Width and height used for comparison
downloadUrl	string	URL to download the generated diff image
originalSize	number	Combined size of both input images in bytes
processedSize	number	Size of the diff output image in bytes

Notes

• Both images are resized to the same dimensions (the maximum of each axis) before comparison.
• The diff image highlights differences in red with opacity proportional to the magnitude of change. Identical or near-identical pixels (difference < 10) are shown as semi-transparent versions of the original.
• Similarity is calculated as the inverse of the average pixel difference across all pixels, expressed as a percentage.
• A similarity of 100% means the images are pixel-identical (at the comparison resolution).
• The diff output is always PNG format regardless of input formats.
• Both images are validated and decoded (HEIC, RAW, PSD, SVG supported) before comparison.
• EXIF orientation is auto-applied on both images before processing.