Modulation transfer function measurement of an infrared focal plane array by use of the self-imaging property of a canted periodic target

Modulation transfer function measurement of a multichannel optical system

We present a new method to measure the modulation transfer function (MTF) beyond the Nyquist frequency of a multichannel imaging system for which all the channels have parallel optical axes. Such a multichannel optical system produces a set of undersampled subimages. If the subimages contain nonredundant information, high spatial frequencies are folded between low spatial frequencies, leading to the possible extraction of frequencies higher than the Nyquist frequency. The measurement of the MTF of the multichannel system leads to the estimation of the resolution enhancement of the final image that can be obtained by applying a postprocessing algorithm to the collection of undersampled subimages. Experimental images are presented to validate this method.

Comparative analysis of techniques for measuring the modulation transfer functions of charge-coupled devices based on the generation of laser speckle

Two methods for measuring the modulation transfer function (MTF) of a charge-coupled device (CCD) that are based on the generation of laser speckle are analyzed and compared. The method based on a single-slit aperture is a quick method, although the measurements are limited to values of less than the Nyquist frequency of the device. The double-slit method permits the measurement of values of as much as some 1.8 times the Nyquist frequency, although it is a slower method because of the necessity to move the CCD. The difference between the MTF values obtained with the two methods is less than 0.1 in magnitude; the root-mean-square error between the two curves is 0.046 (4.6%).

Sharpness limitations in the projection of thin lines by use of the Talbot experiment

Studying the limitations of sharpness in self-images of the Talbot effect leads us to abandon the use of the paraxial assumption. In this respect, we will clarify the self-image concept and show experimentally and theoretically the influence of "nonparaxial effects" on the self-image. The boundary between paraxial and nonparaxial scalar theory is also clarified in this context. The Rayleigh criterion in aberration diffraction theory is adapted for explicit estimations of this boundary and the maximum sharpness of lines projected by use of the Talbot effect.

Talbot experiment re-examined: study of the chromatic regime and application to spectrometry

The original Talbot experiment in white light has been reconstituted, using an amplitude grating made of thin slits and a colour CCD camera and a model has been developed to describe the field diffracted by the grating illuminated in polychromatic light with a known spectral density. Above the historical interest of this study, the possibility of applying this effect to make spectral measurements is explored and a new concept of Talbot spectrometer is proposed.

Liquid-crystal-display projector-based modulation transfer function measurements of charge-coupled-device video camera systems

We demonstrate the ability to measure the system modulation transfer function (MTF) of both color and monochrome charge-coupled-device (CCD) video camera systems with a liquid-crystal-display (LCD) projector. Test matrices programmed to the LCD projector were chosen primarily to have a flat power spectral density (PSD) when averaged along one dimension. We explored several matrices and present results for a matrix produced with a random-number generator, a matrix of sequency-ordered Walsh functions, a pseudorandom Hadamard matrix, and a pseudorandom uniformly redundant array. All results are in agreement with expected filtering. The Walsh matrix and the Hadamard matrix show excellent agreement with the matrix from the random-number generator. We show that shift-variant effects between the LCD array and the CCD array can be kept small. This projector test method offers convenient measurement of the MTF of a low-cost video system. Such characterization is useful for an increasing number of machine vision applications and metrology applications.