 Openholo  v1.0 Open Source Digital Holographic Library
Get Parameter-SF
Collaboration diagram for Get Parameter-SF: ## Functions

double ophSig::sigGetParamSF (float zMax, float zMin, int sampN, float th)
Extraction of distance parameter using sharpness functions. More...

## Detailed Description

This module is related method which extraction of distance parameter using sharpness function maximization method.

# Introduction

• We use autofocusing to capture in-focus images. It is based on sharpness of images and various of autofocusing algorithms have been proposed. It represents a peak when the image is in-focus and drops when the image goes out-of-focus. It can relate to holography signal process. Hologram has a depth information of object and is reconstructed at that point. The sharpness of the reconstructed hologram image changes with the change of the depth position.
• If the depth of focus is not correct, the reconstructed hologram can not have a clear image. It means the same as in-focus image phenomenon. For this reasons, we will discuss the hologram signal processing using the sharpness functions.

# Algorithm

• Brenner function  : A focus function f(Z) is calculated which is a measure of the average change in gray level between pairs of points separated by n pixels. f(Z) is a maximum when the image is in focus. and is given by

$f(Z)=\sum_{j}\sum_{i}\left| G_i(Z)-G_{ij}(Z)\right|^2$

• Where the index (i) ranges over all image points, in order along a scan line (j); n is a small integer; Z is the Z-axis, or focus position; and $$G_i$$ is the transmission gray level for point i. A value of n equal to 2 gives a good signal to noise ratio. Figure 1. Concept of searching distance parameter.
• Reconstruct the hologram to sequential depth positions using Fresnel diffraction method. then we can obtain $$f(Z)$$ of reconstructed hologram image. if $$f(Z)$$ is maximum value, value of $$Z$$ is distance parameter of hologram.

# Reference

•  J. Brenner et al., "An Automated Microscope for Cytologic Research - A Preliminary Evaluation", Journal of Histochemistry and Cytochemistry, vol. 24, no. 1, pp. 100-111, 1976

## ◆ sigGetParamSF()

 double ophSig::sigGetParamSF ( float zMax, float zMin, int sampN, float th )

Extraction of distance parameter using sharpness functions.

Parameters
 zMax maximum value of distance on z axis zMin minimum value of distance on z axis sampN count of search step th threshold value
Returns
result distance

Definition at line 840 of file ophSig.cpp.