Contrast

SourceAFIS » Algorithm » Transparency » Contrast

Contrast, a part of algorithm transparency, is computed during feature extraction for every primary block by taking smoothed histogram for that block, clipping some fraction of brightest and darkest pixels, and taking the difference between brightest and darkest pixel in the remaining histogram. Contrast is used to compute absolute contrast mask and relative contrast mask.

Key	MIME	Filename in ZIP
`contrast`	`application/cbor`	`007-contrast.cbor`

Visualization

Contrast visualization can be computed from this stage's binary data mapped onto blocks and the original fingerprint image. Visualization itself is not part of transparency data.

Contrast visualized as green circles, one per block, with fingerprint image in the background — Contrast map. Circle's surface area is proportional to contrast within that block.

Format

Contrast is a matrix of floating-point numbers encoded in CBOR the same way as decoded image, but X an Y positions correspond to primary blocks rather than pixels and matrix cells contain contrast level in range from 0 (no contrast) to 1 (maximum contrast).

Example: 007-contrast.cbor

{
  "width": 26,
  "height": 25,
  "cells": [
    0.0,
    0.0,
    "... skipped 646 items in range 0.00 to 0.992 ...",
    0.0,
    0.0
  ]
}