Timer

Performance measurement utility for timing internal operations

Overview

The NFIQ2::Timer class provides a simple interface for measuring the execution time of operations. It’s used internally by NFIQ 2 to track the computation speed of quality measure algorithms.

Class Definition

namespace NFIQ2 {
    class Timer {
    public:
        void start();
        double getElapsedTime();
        double stop();
    };
}

Methods

start

void start();

Starts the timer.

Calling start() resets any currently running timer, discarding previous timing data.

Example:

NFIQ2::Timer timer;
timer.start();

getElapsedTime

double getElapsedTime();

Obtains the elapsed time since start() was called, without stopping the timer.

Returns: Elapsed time in milliseconds.

Example:

timer.start();
// ... perform operations ...
double elapsed = timer.getElapsedTime();
std::cout << "Elapsed: " << elapsed << " ms" << std::endl;
// Timer is still running

stop

double stop();

Stops the timer and returns the elapsed time.

Returns: Elapsed time in milliseconds since start() was called.

Example:

timer.start();
// ... perform operations ...
double totalTime = timer.stop();
std::cout << "Total time: " << totalTime << " ms" << std::endl;

Usage Examples

Basic Timing

#include <nfiq2.hpp>

NFIQ2::Timer timer;
timer.start();

// Compute quality score
NFIQ2::Algorithm model;
unsigned int score = model.computeUnifiedQualityScore(image);

double computeTime = timer.stop();
std::cout << "Quality score " << score 
          << " computed in " << computeTime << " ms" << std::endl;

Intermediate Timing

NFIQ2::Timer timer;
timer.start();

// Stage 1
processStep1();
double stage1Time = timer.getElapsedTime();
std::cout << "Stage 1: " << stage1Time << " ms" << std::endl;

// Stage 2
processStep2();
double stage2Time = timer.getElapsedTime() - stage1Time;
std::cout << "Stage 2: " << stage2Time << " ms" << std::endl;

// Total
double totalTime = timer.stop();
std::cout << "Total: " << totalTime << " ms" << std::endl;

Timing Multiple Operations

NFIQ2::Timer timer;
std::vector<double> timings;

for (const auto& image : images) {
    timer.start();
    unsigned int score = model.computeUnifiedQualityScore(image);
    timings.push_back(timer.stop());
}

// Calculate statistics
double avgTime = std::accumulate(timings.begin(), timings.end(), 0.0) / timings.size();
std::cout << "Average time per image: " << avgTime << " ms" << std::endl;

Internal Usage

The Timer class is used internally by quality measure algorithms to track computation speeds. You can access these timings through the QualityMeasures API:

auto algorithms = NFIQ2::QualityMeasures::computeNativeQualityMeasureAlgorithms(image);

// Get algorithm speeds in milliseconds
auto speeds = NFIQ2::QualityMeasures::getNativeQualityMeasureAlgorithmSpeeds(algorithms);

for (const auto& [algorithmID, speedMs] : speeds) {
    std::cout << algorithmID << ": " << speedMs << " ms" << std::endl;
}

Performance Considerations

The Timer uses std::chrono::steady_clock for monotonic time measurement, ensuring accurate results even if the system clock is adjusted.

• Resolution: Microsecond precision on most platforms
• Overhead: Minimal (typically < 1 microsecond)
• Thread Safety: Each Timer instance should be used by a single thread

See Also

Quality Measure Algorithms

View algorithm computation speeds

Performance Guide

Optimize quality measure computation