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"Multiplexing is meant to record a number of different information in a piece of film. The multiplexing is conducted by giving a code to each information prior to the recording. In this research the multiplexing is done with the theta modulation technique, i.e. using a rotated grating so that each information is coded by a certain angular direction of the spatial frequency of the grating. To recover the original information, the demultiplexing is done by filtering the Fourier transform of the multiplexed recording. A spatial filter in the form of a properly oriented slit is located at the Fourier plane to transmit the diffraction pattern of a single information. The limitations to the number of information which could be recorded are the information extent within each object and the linearity characteristics of the film used. The experiment has been conducted using a diffraction grating with a spatial frequency of 14.2 lp/mm. For an exposure speed of 1/1000 second for each information and a grating rotation angle of 1.50, a number of eleven (11) information can be multiplexed. For an exposure speed of 1/2000 second, and a grating rotation angle of 50, eighteen (18) information can be multiplexed."

"Optical differentiation is one of many methods in the optical data processing that is useful for, e.g. image contouring. In this thesis, the differentiation filter is caried out based on the spatial filtering techniques. The ob ject is transformed with a Fourier lens to obtain the spatial frequency spectrum of the object at the Fourier plane. A spatial differentiation filter is placed at the Fourier plane. And finally, with another lens the filtered spectrum is transformed back to obtain the output image. The critical step of the experiment is the design and the fabrication of the filter. In this thesis, two kinds of models have been used to approximate the differentiation filters: (1) multi-step function and (2) Gaussian spot. The multi-step function is intended to approximate the first order differentiation filter. However, due to the photographic limitations, the multi-step function has become a single step function or simply a high-pass filter. Nevertheless, the result may be useful as the approximation of the second (not the first) order differentiation. A filter with a diameter of 0.4 mm appears to give a good result for an object consisting of letters of 4 mm high. To obtain the Gaussian spot, a He-Ne laser beam spot with 6328 nm has been used. with several attenuations, the laser beam spot has been recorded with various shutter speeds in an open camera. It appear that the Gaussian filter is a very good approximation of the second order differentiation filter. Compared to the high-pass filter, it gives higher S/N ratio. The Gaussian spot obtained with a shutter speed of 1/4000 and minimum attenuation gives the best image output. However, none of the filters gives the first order differentiation output."

"In this research a scattering technique employing f or war dscatter of a He-Ne C0,5328 pm, 30 mw) laser beam together with a 1024 x 1024 arrays CCD-V11 video camera as a detector was used for determining both particle size distribution and concentration. For determining the size distribution the "Differential Fourier Transform Technique" is chosen because it does not require matrix inversion or a priori knowledge of functional forms of size and it takes advantage of the Fast Fourier Transform.

Measurements have been performed using this technique on cigarette smoke and smoke coming out, from burning clothes. From the experimental results it is shown that the diameter of cigarette smoke particles is between 0.3 and 1 . 3 pm. similar to that from a previous research C0.O4 - 1.00 pm). The measured size of smoke particles from burning clothes is 0.5 - 1.5 pm. similar to standard data Cabout 1 pm). But the obtained size distribution curves are still rough because of the limited observation scattering angle. It is also shown that the minimum and maximum concentration which can be detected are 1.8 x 107 particles/mma Cor 12.8 ppm) and 12.7 x 100 particles/=O Cor 906 ppm). This means that this technique can be used for measuring air pollutant concentration, as especially from smoke."