Binary Halftone Research Articles

Quantization and truncation conditions of fourier power spectrum for good performance in binary subtracted joint transform correlator

Binary subtracted joint transform correlator (BSJTC) provides sharp autocorrelation peaks and better discrimination for similar targets even though many reference images are arranged regularly in an input scene. The effects of the number of reference patterns, the quantization levels and truncation of the Fourier power spectra on the performance of BSJTC are investigated. The number of effective quantization levels to obtain sharp and clear autocorrelation peaks is estimated by computer simulations using the input scenes with many binary images (alphabetic characters) and halftone images (human portraits). Experimental results of BSJTC are also shown using a hybrid system with a Bi12SiO20 spatial light modulator and a personal computer.

A generalized analysis of binary halftone representation of images

A halftone representation of continuous tone images is a useful method for displaying images on devices that can display only two gray levels, “black” and “white”. We present a detailed and generalized analysis of a binary representation of continuous tone functions, develop analytic expressions of the Fourier spectrum, and discuss the reconstruction error. The discussion makes distinction between spatially continuous and discrete functions. This analysis is applicable to pulse modulation techniques such as pulse width (PWM), pulse density (PDM) or pulse position (PPM) modulation, which are generated in all types of dither and carrier procedures.

Gray level requantization

A distance measure between pictures, that enables comparison of images with different gray level ranges, is described. With such measure halftoning can be treated as an optimization problem. Based on this measure, an algorithm for reducing the number of gray levels of a picture with minimal visual degradation is developed. The algorithm can even produce a binary halftone of the picture, which is needed for many hard copy devices. The complexity of the algorithm is high, and it is not recommended as a daily halftoning method. However, the method provides a well-defined mathematical approach for comparing images.