FingerprintImageData

Binary data representing a decompressed fingerprint image

Overview

The NFIQ2::FingerprintImageData class represents binary data for a decompressed fingerprint image, canonically encoded as per ISO/IEC 39794-4:2019. This class inherits from NFIQ2::Data and adds fingerprint-specific metadata.

Class Definition

namespace NFIQ2 {
    class FingerprintImageData : public Data {
        // Public interface
    };
}

Constants

Resolution500PPI

static const uint16_t Resolution500PPI { 500 };

Standard 500 PPI (pixels per inch) resolution constant.

Constructors

Default Constructor

FingerprintImageData();

Default constructor.

Metadata-Only Constructor

FingerprintImageData(
    uint32_t width,
    uint32_t height,
    uint8_t fingerCode,
    uint16_t ppi);

Constructor that does not store image data.

width · uint32_t

Width of the image in pixels.

height · uint32_t

Height of the image in pixels.

fingerCode · uint8_t

Finger position of the fingerprint in the image.

ppi · uint16_t

Resolution of the image in pixels per inch.

Full Constructor

FingerprintImageData(
    const uint8_t *pData,
    uint32_t dataSize,
    uint32_t width,
    uint32_t height,
    uint8_t fingerCode,
    uint16_t ppi);

Constructor storing image data.

pData · const uint8_t *

Pointer to decompressed 8 bit-per-pixel grayscale image data, canonically encoded as per ISO/IEC 39794-4:2019.

dataSize · uint32_t

Size of the buffer pointed to by pData.

width · uint32_t

Width of the image in pixels.

height · uint32_t

Height of the image in pixels.

fingerCode · uint8_t

Finger position of the fingerprint in the image.

ppi · uint16_t

Resolution of the image in pixels per inch.

Copy Constructor

FingerprintImageData(const FingerprintImageData &otherData);

Copy constructor.

Public Members

width

uint32_t width { 0 };

Width of the fingerprint image in pixels.

height

uint32_t height { 0 };

Height of the fingerprint image in pixels.

fingerCode

uint8_t fingerCode { 0 };

ISO finger code of the fingerprint in the image.

ppi

uint16_t ppi { Resolution500PPI };

Pixels per inch of the fingerprint image. Defaults to 500 PPI.

Methods

copyRemovingNearWhiteFrame

NFIQ2::FingerprintImageData copyRemovingNearWhiteFrame() const;

Obtain a copy of the image with near-white lines surrounding the fingerprint removed.

return · NFIQ2::FingerprintImageData

Cropped fingerprint image.

Throws: NFIQ2::Exception if error performing the crop, or the image is too small to be processed after cropping.

Inherited Methods from Data

Since FingerprintImageData inherits from NFIQ2::Data, the following methods are also available:

readFromFile

void readFromFile(const std::string &filename);

Reads the content from a file into this object.

Throws: NFIQ2::Exception if file cannot be opened.

writeToFile

void writeToFile(const std::string &filename) const;

Writes the content to a file.

Throws: NFIQ2::Exception if file cannot be opened.

toHexString

std::string toHexString() const;

Generates a string in hexadecimal format of the buffer.

Throws: NFIQ2::Exception if no data available in buffer.

fromBase64String

void fromBase64String(const std::string &base64String);

Imports data from a Base64 encoded string.

Throws: NFIQ2::Exception if invalid character is detected in string.

toBase64String

std::string toBase64String() const;

Generates a string in Base64 format of the buffer.

Usage Example

#include <nfiq2_fingerprintimagedata.hpp>

// Create fingerprint image data from raw pixels
uint8_t* pixels = /* ... load image data ... */;
uint32_t width = 640;
uint32_t height = 480;
uint8_t fingerCode = 1;  // Right thumb
uint16_t ppi = NFIQ2::FingerprintImageData::Resolution500PPI;

NFIQ2::FingerprintImageData imageData(
    pixels,
    width * height,
    width,
    height,
    fingerCode,
    ppi
);

// Remove near-white borders
NFIQ2::FingerprintImageData cropped = imageData.copyRemovingNearWhiteFrame();

Image Format Requirements

The fingerprint image must be:

• 8 bit-per-pixel grayscale
• Decompressed (raw pixels)
• Canonically encoded as per ISO/IEC 39794-4:2019

See Also

• Algorithm - Uses FingerprintImageData for quality scoring
• Data - Base class for binary data handling