A displacement measurement technology using phase-encoded target joint transform correlator (PETJTC) is analyzed in detail. A phase mask is generated electronically and applied to encode the target image. Input images include the phase-encoded target image and the reference image. The joint power spectrum of the input images are obtained and encoded by the same phase mask. Through another Fourier transform the brightest peak in relation to displacement between the reference and target image appears in the correlation plane. In contrast to the displacement measurement based on traditional joint transform correlator, PETJTC could efficiently use the space of the input plane such as spatial light modulator, disperse the autocorrelation item into system noises, and leave the cross-correlation items only, which is convenient for detection. The effects of phase mask with different sizes and different types of noises are analyzed. Results based on digital computation show that PETJTC has a higher performance if the phase mask is bigger and has strong robustness under severe noise. Different displacement measurement technologies are contrasted. PETJTC could accurately detect the displacement. Root mean square errors can remain within 0.1 pixel.
Joint transform optical correlator (JTOC) is an effective motion detection tool, and the quality of spectrogram has
great influence on the detection accuracy. In this paper, we constructed simulation software for JTOC and used
two images with known displacement as the experimental objects; we gradually increased the noise in the
spectrogram, and then compared the detection data under noise conditions with the real data to test the degree of
influence of the noise on the detection accuracy. The test results show that when the noise variance is small, the
influence of noise is very little; when the noise variance is more than 0.8, the influence of noise increases
gradually; and when the noise variance exceeds 1.29, the noise will directly cause failure of joint transform
optical correlator.
Since joint transform correlators based on amplitude light modulator have poor light efficiency and low
cross-correlation peak, a displacement measurement method based on spatial light modulator is proposed. After the
input images were coded by phase spatial light modulator, corresponding displacement between the adjacent two
pictures could be detected through the joint transform correlator. Experiments were carried out with under-exposed
images. The experimental results showed that phase joint transform correlators had better discrimination. The proposed
technique is very effective for motion detection under circumstances of low illumination.
KEYWORDS: Video, Bandpass filters, Signal processing, Microscopes, Analog electronics, Electronic filtering, Charge-coupled devices, Video processing, Signal analyzers, Linear filtering
An autofocus system applied to microscope has been designed, which is based on the analysis of analog video signals'
processing. A multi-feedback band-pass active filter retains high frequency components of analog video signals from
CCD, then high frequency components that represent image details information are amplified and performed integral
operation, which is defined as focusing measure. After A/D transformation a MCU controls the focusing procedure and
drives a stepping motor to find focused-position. The selection of bandwidths of filter, selection of focusing windows,
step-size in search and hill climbing algorithms are discussed and optimized to improve focus accuracy and shorten focus
time.
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