Search results for "Optical correlator"
showing 10 items of 13 documents
Shift and scale-invariant correlator using a radially stretched phase-only filter
1995
A radial stretching of the phase only filter depending on the energy angular distribution of the target spectrum is used to perform shift and scale invariant pattern recognition. The complex conjugate of a basic size target Fourier transform and the cumulative energy angular distribution are calculated. Then the radially stretched filter providing the same energy contribution to the correlation peak independent on the target size is prepared and used in a conventional correlator, with spherical-wave illumination. The maximum scale ratio of recognizable objects equals 1:1.5. Computer simulations and experimental results, showing the performance of the filter are presented.
Fullin-situcharacterization of spatial light modulators in an optical correlator. Filter adaptation to operating curves
1998
Abstract In this paper we present one method for the characterization of the spatial light modulators (SLMs) of a real-time Vander Lugt type of correlator. This correlator uses two SLMs: one to introduce the scene and a second to introduce the frequency‐matched filter. The SLM characterization methods are in situ, that is in the correlator set‐up. Illumination conditions are different for each SLM, and consequently different characterization techniques must be used in each case. For the characterization of the scene SLM a diffraction method is used, while for the characterization of the filter SLM an interferometric technique is more convenient. Finally, we take into account the operating c…
Scale-tunable optical correlation with natural light
2008
We describe two different scale-tunable optical correlators working under totally incoherent light. They behave as spatially incoherent wavelength-independent imaging systems with an achromatic point-spread function (PSF). In both cases it is possible to adapt the scale of the achromatic PSF, i.e., to modify the scaling factor of the PSF and preserve the chromatic compensation, by one's shifting the input along the optical axis. The remarkable properties of these systems allow us to carry out a scale-tunable color pattern-recognition experiment with natural light.
All-incoherent dispersion-compensated optical correlator
2007
We report on a simple, spatially incoherent, wavelength-independent imaging system that, in contrast to the conventional case, exhibits a dispersion-compensated point-spread function. Our hybrid (diffractive-refractive) three-lens imaging configuration thus acts as an all-incoherent dispersion-compensated optical irradiance correlator. So the optical arrangement is well adapted to processing color information (both spatially and temporally incoherent) under natural illumination.
Incoherent optical correlator
1990
A nonconventional setup based on the Lau effect is employed for implementing a lensless incoherent correlator of 2-D signals with compact support.
Multiple incoherent 2D optical correlator
1991
Abstract A nonconventional setup, based on the Lau effect, is employed for implementing a lensless version of an incoherent object-space correlator of 2D signals with compact support. Experimental results are also shown.
Experimental multichannel recognition capability of polychromatic objects using optical correlators
1990
Polychromatic object recognition by multichannel correlation is experimentally achieved. Model objects whose shape changes with the wavelength of the illumination beam were used. Highpass matched filters were employed. The results confirm previous numerical simulations 1.
Single-output color pattern recognition using a fractional correlator
1997
A novel method for performing color image pattern recogni- tion using a fractional correlator (FC) is proposed. The input plane is illuminated with three different coherent sources of wavelengths corre- sponding to RGB (red, green, and blue) colors. The output plane pro- vides a single output peak, which is a result of an incoherent addition between the three correlations obtained per each color. By using the fractional correlator, which is a partially space variant correlator, we achieve space-variance-controlled color pattern recognition. The use of the three-color illumination can drastically increase the discrimination ability of the suggested correlator. © 1997 Society of Photo-Optical…
Phase joint transform sequential correlator for nonlinear binary correlations
2005
We study the performance of nonlinear optical correlations using a joint transform correlator that operates in phase-only spatial light modulation at input joint transform plane. Amplitude input nonlinear optical time sequential correlations have shown better discrimination and noise robustness than conventional linear correlations. Those nonlinear correlations are based on decomposing the reference and the target into binary slices and to add the contribution of all linear correlations between them. Those correlations can be easily implemented using a conventional joint transform correlator. However, the system has poor efficiency and low cross-correlation peak intensity, mainly because of…
Target localization in the three-dimensional space by wavelength multiplexing.
2002
A method to localize a target in the three-dimensional space is presented. Each different position of the target on the depth axis produces, when captured with a CCD camera, an image of a different size on its sensor plane. The size of this image depends only on the distance between the target and the camera. The use of a white light optical correlator that gives us a different response depending on the scale of the input image permits us to know the depth position of the particular target. The obtained results demonstrate the utility of the newly proposed method.