Hua-Kuang Liu

Linear versus logarithmic spatial filtering in the removal of multiplicative noises.

Linear and logarithmic coherent spatial-filtering techniques are compared in the separation of multiplicative noise from an image in a coherent-optical image-processing system. It is demonstrated that both techniques are effective in the removal of simple grating-type high-frequency noises, but that linear filtering cannot remove noise of spatial frequencies lower than 5 lines/cm, whereas logarithmic filtering can.

White-light image addition and subtraction by colorimetric measurement

The theory and experiment of a new white-light image-processing technique for black-and-white image addition and subtraction by means of Fourier-plane spatial color filtering are described. Both the intensity transmittances of three (or two) processed images and the results of the addition and subtraction are expressed in a chromaticity coordinate system.

New and direct optical analog-to-digital conversion method

A new method for performing direct optical analog-to-digital conversion is presented. The technique requires utilization of a specifically designed and fabricated conversion screen. Either coherent or incoherent light sources may be used; hence a wide range of applications is possible. Arithmetic operations of the resultant digital outputs are defined so that the technique can be used to make real-time preprocessors for optical logic circuits, such as half adders or residue-arithmetic optical computers.

White-light stereoprojection through Fourier spectrum polarization

Theory and experiments of a new stereoprojection technique that uses a white-light optical image-processing system are described. The stereoprojection can be accomplished in two steps: (1) spatial encoding of stereoscopically coupled images and (2) spatial polarization filtering at the Fourier plane in a white-light optical image processor. Compared with existing stereoprojection methods, the present technique requires only one projector and a single piece of encoded film; therefore it is much simpler and more economical to use for practival applications.

Analysis of image reproduction using a linear line screen

An important criterion for the highest-fidelity image reproduction by the use of a one-dimensional halftone screen (or line screen) possessing linear cell transmittance is theoretically established. The criterion can be used as a guideline for optimum screen design and image reproduction.

All-optical homomorphic image-processing system

An optical homomorphic system obtained by the use of the halftone technique has been realized that involves the effective use of a logarithmic and an exponential contact screen. Logarithmic filtering alone is able to separate the multiplicative noise. But the application of exponential processing on the logarithmically operated image restores the image and completes the homomorphic system.

Real-time white-light pseudocolor image-difference detection technique.

The principles and an experimental demonstration of a real-time image-difference detection technique are described. In the technique, two input transparencies are illuminated by a white-light source through two different primary-color filters. A Wollaston prism is used to combine the two inputs into a synthetic pseudocolor image. The differences between the two inputs are revealed from the colors of that synthetic image.

Analysis of tone reproduction with square, circular, and concentric-ring patterned screens of linear cell transmittance

The optimum parameters for high-fidelity image reproduction by halftone contact screens of square, circular, and concentric-ring cell patterns possessing linear optical transmittance are presented. Our theoretical analysis finds that, in comparison, the screens of concentric-ring patterns can achieve better reproduction fidelity.