Generalized demodulation technique for obtaining three-dimentional digital images and its software implementation
Abstract
The paper proposes the complex technique of demodulation, which can be applied for obtaining three-dimensional digital images in optical microscopes. This technique allows to calculate the contrast of harmonic spatial modulation with arbitrary values of phase angles. The input data is a stack of digital images with harmonic spatial modulation. Three digital images with different phases of modulation obtained in the same focus position are processed to get one data set about the contrast distribution. This data makes possible to compose the three-dimensional images by selection of the maximal values of the contrast in three-dimensional space. The paper contains the analytical solution of the system with three linear equations that helps to identify the principal parameters of harmonic spatial modulation, including its average value and contrast. As a result, the expression for contrast calculation is present in an analytical form. This expression is valid for any modulation phase angles that do not coincide. The paper contains the Python code of two functions, that illustrate the procedure of obtaining the three-dimensional images. This code demonstrates how to calculate the contrast and how to build the three-dimensional surface image as a composition of the contrast distribution map and the corresponding height map. This code can be improved for composing color three-dimensional surface images, color three-dimensional images in form of the image stacks or by application of the software packages for parallel computing. The advantage of the proposed technique is the possibility of using economic units to form a harmonious spatial modulation. These units can be installed on most optical microscopes with digital cameras and motorized focusing drives without purchasing expensive commercial software. It significantly reduces the price of transforming these optical microscopes into the instrument for obtaining digital three-dimensional images
Keywords
digital image processing; three-dimensional digital image; spatial modulation of lighting; optical microscope; demodulation
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