Guoqiang Ni

Contrast-based image fusion using the discrete wavelet transform

We introduce a contrast-based image fusion method using the wavelet multiresolution analysis. This method includes three steps. First, the multiresolution architectures of the two original input images are obtained using the discrete wavelet transform. A new concept called directive contrast is presented. Second, the multiresolution architecture (MRA) of the fused image can be achieved by selecting the corresponding subband signals of each input image based on the directive contrast. Finally, the fused image is reconstructed using the inverse wavelet transform. This algorithm is relevant to visual sensitivity and is tested by merging visual and IR images. The result shows that the fused image can integrate the details of each original image. The visual aesthetics and the computed SNRs of the fused images show that the new approaches can provide better fusion results than some previous multiresolution fusion methods.

Visual and infrared dual-band false color image fusion method motivated by Land's experiment

A new false color image fusion method is proposed on the basis of Lands experiment on color constancy of human vision, through idealized hypothesis of the red filter and green filter, through equienergy distribution hypothesis of the light source, and by relating the infrared and visual images to the black-and-white transparencies obtained through the red and green filters of Lands experiment, respectively. The normalization of each color channel conforms with the von Kries chromatic adaptation model and the maximum red-green-blue method, which has been popularly adopted in some video systems and color theories to estimate the illumination color and which, to a certain extent, agrees with the color constancy of human vision. The method has been proven effective after it was compared with Toet et al.s fusion method. Its colorfulness is enhanced by the strategy of assigning the difference between the source images to the blue channel, which is used in Toet et al.s algorithm to underscore the characteristic components of the individual images. The additional opponent processing neurodynamic equation of the center-surround receptive field can improve the output contrast significantly and is believed to be more suitable for revealing details by human observers. Some perceptual evaluation results are also given at the end.

Method for suppressing the quantization error of Newton’s rings fringe pattern

Abstract. Newton’s rings fringe pattern is often encountered in optical measurement. The digital processing of the fringe pattern is widely used to enable automatic analysis and improve the accuracy and flexibility. Before digital processing, sampling and quantization are necessary, which introduce quantization errors in the fringe pattern. Quantization errors are always analyzed and suppressed in the Fourier transform (FT) domain. But Newton’s rings fringe pattern is demonstrated to be a two-dimensional chirp signal, and the traditional methods based on the FT domain are not efficient when suppressing quantization errors in such signals with large bandwidth as chirp signals. This paper proposes a method for suppressing quantization errors in the fractional Fourier transform (FRFT) domain, for chirp signals occupies little bandwidth in the FRFT domain. This method has better effect on reduction of quantization errors in the fringe pattern than traditional methods. As an example, a standard Newton’s rings fringe pattern is analyzed in the FRFT domain and then 8.5 dB of improvement in signal-to-quantization-noise ratio and about 1.4 bits of increase in accuracy are obtained compared to the case of the FT domain. Consequently, the image quality of Newton’s rings fringe pattern is improved, which is beneficial to optical metrology.

Indoor Positioning Method Based on Metameric White Light Sources and Subpixels on a Color Image Sensor

An indoor positioning method based on metameric white light sources and subpixels on a color image sensor is proposed in this paper. Metameric white light sources are obtained by merging multiple-color light-emitting diode (LED) chips with different intensity ratios. The output intensity ratios of subpixels on color image sensor at the receiver are employed to identify the respective metameric white light sources. Proof of concept experiments demonstrates that the average error of 2-D indoor positioning is 1.50 cm and 3-D indoor positioning is 3.58 cm. The indoor positioning system with the proposed method is cost effective and convenient because image sensors in nowadays available mobile devices can be utilized.

Iterative positioning algorithm to reduce the impact of diffuse reflection on an indoor visible light positioning system

Recently, indoor visible light localization has become attractive. Unfortunately, its performance is limited by diffuse reflection. The diffuse reflection is estimated by the bilinear interpolation-based method. A received signal strength-based iterative visible light positioning algorithm is proposed to reduce the influence of diffuse reflection by subtracting the estimated diffuse reflection signal from the received signal. Simulations are made to evaluate the proposed iterative positioning algorithm in a typical scenario with different parameters of the field-of-view (FOV) of the receiver and the reflectivity of the wall. Results show that the proposed algorithm can reduce the average positioning error by 12 times in a typical scenario and can reduce the positioning error greatly with various FOV of the receiver and the reflectivity of the wall. The proposed algorithm is effective and robust to reduce the degradation caused by diffuse reflection in a positioning system and will have many potential applications in indoor localization scenarios.

Application of Fractional Fourier transform for interferometry

The Fractional Fourier transform can be understood as a chirp-based decomposition. Accordingly it can be used to process fringe patterns with quadratic phase, including denoising, quantization error reduction, sampling and reconstruction, and phase derivative estimation.

Method for reducing Newton's rings pattern in the scanned image reproduced with film scanners

Newton’s rings pattern always blurs the scanned image when scanning a film using a film scanner. Such phenomenon is a kind of equal thickness interference, which is caused by the air layer between the film and the glass of the scanner. A lot of methods were proposed to prevent the interference, such as film holder, anti-Newton’s rings glass and emulsion direct imaging technology, etc. Those methods are expensive and lack of flexibility. In this paper, Newton’s rings pattern is proved to be a 2-D chirp signal. Then, the fractional Fourier transform, which can be understood as the chirp-based decomposition, is introduced to process Newton’s rings pattern. A digital filtering method in the fractional Fourier domain is proposed to reduce the Newton’s rings pattern. The effectiveness of the proposed method is verified by simulation. Compared with the traditional optical method, the proposed method is more flexible and low cost.

Color image enhancement using a multiple-scale opponent neural network

One goal of image processing is to recreate the human visual perception of the original scene. We offer a method of color image enhancement for realistic image display. The algorithm is based on a special implementation of the feed-forward ON-OFF shunting neural network. The properties of the neural network for image processing are first investigated. The computational simulations make clear the strengths and weaknesses of the neural network. Combined with a brightness-based tone reproduction operator, a multiscale extension to the neural network is developed to correct the original versions weaknesses and provides a coherent framework for color image enhancement. The algorithm achieves both dynamic range compression and vivid color rendition and qualitatively approaches the aspects of early visual perception. Extensive tests demonstrate that this method could produce satisfying images without any unexpected results.