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The discrimination capability requirements of pattern recognition systems may vary depending on the application and the characteristics of the objects to analyse. Our goal is to obtain a single system with a wide and smooth control of its discrimination capability in two senses: the first one, a discrimination capability selective to different aspects of the target (for example, shape, intensity, colour, texture); the second one, a discrimination capability with variable level of sensitivity -or tolerance- to the differences between an object and the target in the aspect selected. This purpose lead us to consider higher levels of complexity in the sensitivity of the recognition system. Thus, we obtain pattern recognition with high discrimination capability for a given aspect along with certain tolerance for another aspect, or vice versa. In this work, we build an optoelectronic system for pattern recognition with selective and adjustable discrimination capability by applying a dual nonlinear correlation model to a joint transform correlator. Dual nonlinear correlation is achieved by means of two nonlinear operators that are applied to both the reference and input channels. A filtering function that limits the region of support in the Fourier plane is additionally introduced. The eventual capabilities of the real system strongly depend on some experimental conditions such as quantization, grey-level dynamic range, saturation and other technical characteristics of both the camera and the spatial light modulator used in the joint transform correlator. We explore these capabilities for a 8-bits and a 12-bits CCD camera and several available modulators. Experimental and simulated results for model and real objects - alphabetic characters, keys and screws- are presented and discussed. They demonstrate that the discrimination capability of the optical recognition system by dual nonlinear correlation can be controlled and adjusted with gradable tolerance to object variations in a given aspect.
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