Real-time optical image subtraction and edge enhancement using ferroelectric liquid-crystal devices based on speckle modulation

Real-time edge detection by cyclic-path polarization interferometer

In a triangular path cyclic interferometer employing a polarizing beam splitter (PBS), the two counterpropagating beams are orthogonally polarized. A sample placed almost equidistant from the PBS is imaged by a lens placed in the path of the emerging beams so that two defocused images of the sample are recorded on a CCD. Using a linear polarizer in the path of the orthogonally polarized imaging beams, it is possible to achieve amplitude subtraction between the two images, resulting in an edge-enhanced image of the sample. The proposed real-time edge-enhancement technique is experimentally demonstrated.

Orientation-selective edge detection and enhancement using the irradiance transport equation

We present a method for orientation-selective edge detection and enhancement based on the irradiance transport equation. The proposed technique distinguishes the sign of the derivative of the intensity pattern along an arbitrarily selected direction. The method is based on the capacity of liquid-crystal displays to generate simultaneously a contrast reverted replica of the image displayed on it. When both images (the original one and its replica) are imagined across a slightly defocused plane, one obtains an image with enhanced first derivatives. Unlike most Fourier methods, the proposed technique works well with a low-coherence light source, and it does not require precise alignment. The proposed method does not involve numerical processing, and thus it could be potentially useful for processing large images in real-time applications. Validation experiments are presented.

Programmable birefringent lenses with a liquid-crystal display

We study the properties of a novel birefringent lens constructed by combination of a regular glass lens and a programmable diffractive lens addressed to a liquid-crystal display (LCD). The LCD affects only the vertical polarization state. Consequently the birefringent lens produces two images of an input object with different locations and magnifications for the two orthogonal polarization states. Using a properly oriented analyzer polarizer produces interference fringes. We then show how the imaging system acts as a common-path polarization interferometer for wave-front analysis of objects in the input plane. Finally, we subtract the two images to produce an edge-enhanced version of the input image. All these effects can be controlled because we can program lenses with different focal lengths onto the LCD.