2 research outputs found
Full-field calibration and compensation of lateral chromatic aberration based on unwrapped phase
Lateral chromatic aberration (CA) of color cameras has great effects on the imaging quality. This paper presents a novel
method to full-field calibrate lateral CA between color channels by using unwrapped phase data. Closed circle sinusoidal
fringe patterns having the optimum three-fringe numbers are generated and displayed on a liquid crystal screen
consecutively through red, green and blue channels. These closed fringe patterns are captured by a color camera. The
wrapped phase and unwrapped phase of each pixel can be calculated by using four-step phase shifting algorithm and
optimum three-fringe number method, respectively. The pixel deviations produced by lateral CA are computed by
comparing the obtained absolute phase data between red, blue, and green channels in polar coordinate system and
calibration is accomplished in Cartesian coordinate system. Lateral CA between color channels of the color camera can
be compensated by using the calibrated data. Simulated and experimental results show the validity of the proposed
calibration and compensation method
Lossless compression of color filter array mosaic images with visualization via JPEG 2000
Digital cameras have become ubiquitous for amateur and professional applications. The raw images captured by digital sensors typically take the form of color filter array (CFA) mosaic images, which must be "developed" (via digital signal processing) before they can be viewed. Photographers and scientists often repeat the "development process" using different parameters to obtain images suitable for different purposes. Since the development process is generally not invertible, it is commonly desirable to store the raw (or undeveloped) mosaic images indefinitely. Uncompressed mosaic image file sizes can be more than 30 times larger than those of developed images stored in JPEG format. Thus, data compression is of interest. Several compression methods for mosaic images have been proposed in the literature. However, they all require a custom decompressor followed by development-specific software to generate a displayable image. In this paper, a novel compression pipeline that removes these requirements is proposed. Specifically, mosaic images can be losslessly recovered from the resulting compressed files, and, more significantly, images can be directly viewed (decompressed and developed) using only a JPEG 2000 compliant image viewer. Experiments reveal that the proposed pipeline attains excellent visual quality, while providing compression performance competitive to that of state-of-the-art compression algorithms for mosaic images