标签
PostgreSQL , 指纹 , printfinger , pgafis , 特征值 , 索引
背景
pgafis是一个插件，支持存储指纹特征值，同时将指纹特征比对算法作为UDF编写到了数据库中，安装这个插件依赖指纹比对算法库。
https://www.nist.gov/services-resources/software/nist-biometric-image-software-nbis
https://github.com/lessandro/nbis
pgafis插件代码地址
https://github.com/hjort/pgafis
pgafis
pgAFIS - Automated Fingerprint Identification System support for PostgreSQL
Sample fingerprints data
Table "public.fingerprints"
Column | Type | Modifiers
--------+--------------+-----------
id | character(5) | not null
pgm | bytea |
wsq | bytea |
mdt | bytea |
xyt | text |
Indexes:
"fingerprints_pkey" PRIMARY KEY, btree (id)
- "pgm" stores original raw fingerprint images (PGM)
- "wsq" stores compressed fingerprint images (WSQ)
- "mdt" stores fingerprint templates in XYTQ own binary format (MDT)
- "xyt" stores fingerprint minutiae data in text format
afis=>
SELECT id,
length(pgm) AS raw_bytes,
length(wsq) AS wsq_bytes,
length(mdt) AS mdt_bytes,
length(xyt) AS xyt_chars
FROM fingerprints
LIMIT 5;
id | pgm_bytes | wsq_bytes | mdt_bytes | xyt_chars
-------+-----------+-----------+-----------+-----------
101_1 | 90015 | 27895 | 162 | 274
101_2 | 90015 | 27602 | 186 | 312
101_3 | 90015 | 27856 | 146 | 237
101_4 | 90015 | 28784 | 154 | 262
101_5 | 90015 | 27653 | 194 | 324
(5 rows)
Acquisition
Image Compression (WSQ)
afis=>
UPDATE fingerprints
SET wsq = cwsq(pgm, 2.25, 300, 300, 8, null)
WHERE wsq IS NULL;
- compressed image in WSQ format can be generated from original fingerprint raw image (PGM format)
Feature Extraction (XYT)
afis=>
UPDATE fingerprints
SET mdt = mindt(wsq, true)
WHERE mdt IS NULL;
- minutiae data (features) can be extracted from compressed WSQ image and stored in own binary format (MDT)
Verification (1:1)
afis=>
SELECT (bz_match(a.mdt, b.mdt) >= 20) AS match
FROM fingerprints a, fingerprints b
WHERE a.id = '101_1' AND b.id = '101_6';
match
-------
t
(1 row)
- given two fingerprint templates, they can be considered the same according to a threshold value (e.g., 20) defined by the application
Identification (1:N)
afis=>
SELECT a.id AS probe, b.id AS sample,
bz_match(a.mdt, b.mdt) AS score
FROM fingerprints a, fingerprints b
WHERE a.id = '101_1' AND b.id != a.id
AND bz_match(a.mdt, b.mdt) >= 23
LIMIT 3;
probe | sample | score
-------+--------+-------
101_1 | 101_2 | 23
101_1 | 101_4 | 24
101_1 | 101_5 | 27
(3 rows)
- sequential scan is performed on the table, but so far as a given number of templates (e.g., 3) having a match score above the defined threshold (e.g., 23)
afis=>
SELECT a.id AS probe, b.id AS sample,
bz_match(a.xyt, b.xyt) AS score
FROM fingerprints a, fingerprints b
WHERE a.id = '101_1' AND b.id != a.id
AND bz_match(a.mdt, b.mdt) >= 20
ORDER BY score DESC;
probe | sample | score
-------+--------+-------
101_1 | 101_6 | 28
101_1 | 101_5 | 27
101_1 | 101_8 | 26
101_1 | 101_2 | 23
101_1 | 101_4 | 23
(5 rows)
- "xyt" text field can be used for matching as well
