Absolute contrast mask

SourceAFIS » Algorithm » Transparency » Absolute contrast mask

Absolute contrast mask, a part of algorithm transparency, is a set of primary blocks where contrast falls below some fixed threshold. It is computed during feature extraction. Absolute contrast mask contributes to combined mask.

Key	MIME	Filename in ZIP
`absolute-contrast-mask`	`application/cbor`	`008-absolute-contrast-mask.cbor`

Visualization

Absolute 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.

Absolute contrast mask visualized as yellow masked out area around fingerprint image — Absolute contrast mask. Yellow area consists of blocks excluded due to low contrast.

Format

Absolute contrast mask is a matrix (2-dimensional array) of boolean values. Every cell in the matrix corresponds to primary block. Cell value is true if the block has low contrast and false if it has high contrast. The mask is encoded in CBOR:

width - Horizontal block count.
height - Vertical block count.
cells - Array of width * height booleans representing block contrast. The 2-dimensional block coordinates are mapped into 1-dimensional array by sorting blocks by Y position top to bottom and then by X position left to right.

Example: 008-absolute-contrast-mask.cbor

{
  "width": 26,
  "height": 25,
  "cells": [
    true,
    true,
    "... skipped 646 items ...",
    true,
    true
  ]
}