Sergey N. Starikov

Input scene restoration in pattern recognition correlator based on digital photo camera

Diffraction image correlator based on commercial digital SLR photo camera was reported earlier. The correlator was proposed for recognition of external scenes illuminated by quasimonochromatic spatially incoherent light. The correlator hardware consists of digital camera with plugged in optical correlation filter unit and control computer. The kinoform used as correlation filter is placed in a free space of the SLR camera body between the interchangeable camera lens and the swing mirror. On the other hand, this correlator can be considered as a hybrid optical-digital imaging system with wavefront coding. It allows not only to recognize objects in input scene but to restore, if needed, the whole image of input scene from correlation signals distribution registered by SLR camera sensor. Linear methods for image reconstruction in the correlator are discussed. The experimental setup of the correlator and experimental results on images recognition and input scenes restoration are presented.

Pattern recognition correlator based on digital photo camera

Diffraction image correlator based on commercial digital SLR photo camera is described. The correlator is proposed for recognition of external 2-D and 3-D scenes illuminated by quasimonochromatic spatially incoherent light. Principal optical scheme of the correlator is analogous to that of incoherent holographic correlator by Lohmann. The correlator hardware consists of digital camera with attached optical correlation filter unit and control computer. No modifications have been introduced in units of commercial digital SLR photo camera. Digital camera was connected via camera interface to computer for controlled camera shooting, transfer of detected correlation signals and post-processing. Two ways were used for correlation filter unit mounting. In the first case, correlation filter was attached to the front of the camera lens. In the second one, it was placed in a free space of the SLR camera body between the interchangeable camera lens and the swing mirror. Computer generated Fourier holograms and kinoforms were used as correlation filters in experiments. The experimental setup of the correlator and experimental results on images recognition are presented. The recognition of test objects of direct and reversed contrast with the same correlation filter was performed.

Using commercial photo camera's RAW-based images in optical-digital correlator for pattern recognition

In optical-digital correlators for pattern recognition, linear registration of correlation signals is significant for both of recognition reliability and possible input image restoration. This usually achieves with scientific graduated technical cameras, but most of commercial digital cameras now have an option of RAW data output. With appropriate software and parameters of processing, it is possible to get linearized image data from photo cameras RAW file. Application of such photo cameras makes optical-digital systems cheaper, more flexible and brings along their wider propagation. For linear registration of correlation signals, open-source Dave Coffinss RAW converter DCRAW was used in this work. Data from photo camera were linearized by DCRAW converter in totally RAW documental mode with 16-bit output. Experimental results of comparison between linearized and non-linearized correlation signals and digitally restored input scene images are presented. It is shown, that applied linearization allows to increase linear dynamic range for used Canon EOS 400D camera more that 3 times.

Light spectrum and image-structure correlator

In this paper, an incoherent holographic light spectrum and image structure correlator is considered. This type of correlator includes characteristics of such devices as Lohmanns image correlator and the light spectrum correlator. The light spectrum correlator performs mutual correlation between spectral components of input light and reference spectral components distribution recorded in memory.

Incoherent acousto-optic image correlator with the kinoform

Fourier holograms are commonly used for reference images storing in diffraction correlators with spatially coherent or spatially incoherent illumination. Kinoforms can be a real alternative to Fourier holograms in the correlators. The kinoform represents a computer-synthesized optical element which performs only a phase modulation of a light wave. The kinoform restores true intensity of the recorded image and random distribution of phase. Therefore, it can be utilized for storing reference images, first of all, in correlators with spatially incoherent illumination. The absence of carrier frequency reduces demanded number of pixels of the spatial light modulator being used. Since the kinoform provides reconstruction of reference image in zero diffraction order, requirement on monochromaticity of illumination are decreased as well. The diffraction correlator with the kinoform used as spatial frequency filter is considered. The 2-D acoustooptic deflector was employed to form input images in real time by monochromatic spatially incoherent light. The reference images were recorded on the commercially available kinoforms. The input and reference images were of 256×256 pixels and 200×200 pixels respectively. Since input images were consisted of approximately 400 pixels with non-zero brightness, the image update frequency was gained at 200 Hz. The experimental setup and experimental results on images recognition are presented.

Noncoherent correlator with reflective volume holographic filter

Experimental setup of the correlator with polychromatic spatially incoherent illumination is created. The functions of memory element and spectral selector are executed by the reflective volume Fourier-hologram. The correlation analysis of the test objects was performed. The experimental results of the correlation analysis were obtained both in quasi- monochromatic spatially incoherent and in polychromatic light. Estimations of space bandwidth product of the correlator and its power efficiency depending on parameters of the reflective volume holographic filter were obtained.

Linear methods for input scenes restoration from signals of optical-digital pattern recognition correlator

Linear methods of restoration of input scenes images in optical-digital correlators are described. Relatively low signal to noise ratio of a cameras photo sensor and extensional PSFs size are special features of considered optical-digital correlator. RAW-files of real correlation signals obtained by digital photo sensor were used for input scenes images restoration. It is shown that modified evolution method, which employs regularization by Tikhonov, is better among linear deconvolution methods. As a regularization term, an inverse signal to noise ratio as a function of spatial frequencies was used. For additional improvement of restorations quality, noise analysis of boundary areas of the image to be reconstructed was performed. Experimental results on digital restoration of input scenes images are presented.

Optical information processing systems with various structure incoherent radiation

Since the moment of laser appearance and till now the attention concentrated on great potentiality realization of coherent optical data processing systems. However, the difficulties occurred in creating the workable systems of this type were the reasons of spreading the field of investigation on diffraction systems in which not only the coherent, but the partially coherent and non-coherent illumination is used. Spatial coherence and light spectrum components as well as amplitude, phase and polarization of light passed through the optical system can be modulated by the information to be processed. The transformation of spatial coherence allows to perform Fourier and correlation analysis of images or temporal signals formed by spatially incoherent quasimonochromatic light, when the traditional holographic matched filter is used. The input of two-dimensional data arrays can be performed by the acousto-optic deflector. Developed method of bipolar holographic filter pulse response synthesis increases image recognition reliability. If the light is non- monochromatic it is possible to involve the spectral components as the information parameters in correlation signal formation due to the special modulating mask placed in reference beam when the filter is recorded. A possibility of optical system creation with no lens for image formation based on spatial coherence transform is considered.

Nano-meter scale modifications on material surfaces induced by soft x-ray laser pulse irradiations

To study the interactions between a soft x-ray laser (SXRL) and various materials, we irradiated Al, Au, Cu, and Si with the SXRL beam pulses having a wavelength of 13.9 nm and duration of 7 ps. Following the irradiation, the induced structures were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, conical structures were observed on the Al surface, and ripple-like structures were formed on the Au and Cu surfaces. The conical structures were destroyed under multiple SXRL pulse irradiation. On the other hand, the developments of modified structures were observed after multiple pulse irradiations on the Au and Cu surfaces. On the Si surface, deep holes, that seemed to be molten structures induced by the accumulation of multiple pulse irradiations, were found. Therefore, it is concluded that the SXRL pulse irradiations of various material surfaces cause different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties of each materials, such as the melting point and the attenuation length of x-rays.

Using spatially varying pixels exposure technique for increasing accuracy of the optical-digital pattern recognition correlator

The registration of correlation signals with high dynamic range leads to increase of recognitions accuracy and robustness. Digital photo sensors with common Bayer colour filter array can be used for this purpose. In case of quasimonochromatic illumination used in optical-digital correlator, it is possible to register correlation signals with high dynamic range. For signals registration it can be used not only colour channel, which corresponded to the wavelength of illumination, but other colour channels too. In this work the application of the spatially varying pixels exposures technique for obtaining linear high dynamic range images of correlation signals from digital photo sensors with Bayer mosaic is presented. Bayer colour filters array is considered as an array of attenuating filters in a quasimonochromatic light. Images are reconstructed using information from all colour channels and correction coeficients that obtained at the preliminary calibration step. The registered image of the correlation signal is mapped to the linear high dynamic range image using a simple and eficient algorithm. Calibration procedure for correction coeficients obtaining is described. Quantitative estimation of optical-digital correlators accuracy is provided. Experimental results on obtaining images of correlation signals with linear high dynamic range are presented.