Chenfei Jin

Salient target detection based on pseudo-Wigner-Ville distribution and Rényi entropy

We present what we believe to be a novel method based on pseudo-Wigner-Ville distribution (PWVD) and Rényi entropy for salient targets detection. In the foundation of studying the statistical property of Rényi entropy via PWVD, the residual entropy-based saliency map of an input image can be obtained. From the saliency map, target detection is completed by the simple and convenient threshold segmentation. Experimental results demonstrate the proposed method can detect targets effectively in complex ground scenes.

Gain-modulated three-dimensional active imaging with depth-independent depth accuracy

We present a three-dimensional imaging method using a pulsed laser as a flood illuminating source and an intensified camera as the receiver with exponentially modulated gain. The depth map of a scene is obtained from two intensity images and the depth accuracy is independent of the depth of the target in the scene. We demonstrate a depth-independent depth accuracy of 0.32 m in an indoor experiment and obtain a depth map of an outdoor scene ranging from 150 to 180 m under a lower signal to noise ratio condition.

Improvement of range accuracy of range-gating laser radar using the centroid method.

An improved processing approach based on the relation between range accuracy and slicing number is proposed to improve the range accuracy of range-gating laser radar. The sequence of time-slice images is segmented according to their optimal slicing number and processed in segments to achieve the range information of objects. Experimental results indicate that the slicing number has a significant impact on range accuracy, and the highest range accuracy can be achieved when the systems work with an optimal slicing number.

Scannerless three-dimensional imaging using a pulsed laser and an intensified charge-coupled device with linearly modulated gain

We have developed a scannerless three-dimensional imaging approach that uses a pulsed laser to illuminate a target and an intensified charge-coupled device as the receiver with linearly modulated gain in gated time. The target range is extracted by processing an intensity image with linearly modulated gain and an intensity image with constant gain. Feasibility of the approach is demonstrated by an indoor experiment. Our prototype system can produce 256x256 pixel range images at a 20 Hz frame rate in an outdoor test. The test results indicate that range accuracy is related to the slope coefficient and initial value of the modulated gain.

Multipulse gate-delayed range gating imaging lidar

We present a technique to reconstruct a higher resolution of depth map of range gating imaging lidar by applying the delays of the gates to a typical range gating lidar system during the detection of each returned laser pulse with the encoding of the returned signal. With the consequent delays of the gate, the depth of the scene is extended accordingly. A multipulse gate-delayed range gating lidar system is designed to prove the resolution improvement from 6 to 1.5 m. The unchanged peak power of the laser, the widths of the laser pulse and the sampling period result in a simple structure of the lidar system.

Hopfield neural network-based image restoration with adaptive mixed-norm regularization

To overcome the shortcomings of traditional image restoration model and total variation image restoration model, we propose a novel Hopfield neural network-based image restoration algorithm with adaptive mixed-norm regularization. The new error function of image restoration combines the L2-norm and L1-norm regularization types. A method of calculating the adaptive scale control parameter is introduced. Experimental results demonstrate that the proposed algorithm is better than other algorithms with single norm regularization in the improvement of signal-to-noise ratio (ISNR) and vision effect.

Imaging lidar for occluded target recognition

The detection and recognition performance of photoelectric detector for occluded target is very important in complicated battlefield environment. It is one of the key factors to win a battle. Three key techniques of imaging lidar for occluded target recognition are investigated, including the range-gated scannerless imaging, determination of range gate, spectrum and polarization imaging. The range gate is determined by using modulated gain, pulse width measurement and inference distinguishing of ground object echo and movement flatform. The project of an imaging lidar for occluded target recognition is designed through the combination of hardware and software algorithm.

Virtual ghost imaging with partially coherent hyperbolic cosine Gaussian beam through turbulence

Based on the classical optical coherence theory, a single detector virtual ghost imaging (VGI) with partially coherence hyperbolic cosine Gaussian beam has been demonstrated theoretically. An analytical imaging formula is obtained and the numerical calculation results lead to the influences of the turbulence strength, the propagation distance and the coherent parameters of the beam on the imaging quality. Moreover, we find that the VGI with hyperbolic cosine Gaussian beam can resolve the target better than the VGI with the conventional Gaussian Schell model beam under similar conditions.

Investigation of range accuracy of gain-modulated laser range imaging

A gain-modulated laser range imaging technology is generalized and its range accuracy is deduced. Theoretical results indicate that the range accuracy is proportional to the ratio of gain function to the derivative of the gain function and inverse proportional to output SNR. A gain-modulated laser range imaging system is established in our laboratory. It consists of a pulsed laser which is capable of generating laser pulses with a pulse width of 10ns and a center wavelength of 532 nm, and a receiver which is a digital 256×256 CCD sensor coupled to a GEN II intensifier with a 10nm bandwidth optical filter. Image intensifier is electronically driven and can be set to three modulated gain or constant gain. A range image of the target can be extracted by processing an intensity image with modulated gain and an intensity image with constant gain. Some indoor experiments are performed with sinusoidal, linear and exponential gain functions. The range images of the targets from 52 m to 58 m is taken and analyzed. Experimental results demonstrate the range accuracy with both sinusoidal and linear gain function depends on the relative range but one with exponential gain function independent of relative range. Specially, in the exponential gain function case the relatively small time constant can contribute to relatively high range accuracy.

Scannerless gain-modulated three-dimensional laser imaging radar

Scannerless laser imaging radar will be the trend of laser imaging radar in future because it has several advantages of high frame rate, wide field of view, small size and high reliability owing to giving up mechanical scanner. A scannerless gain-modulated three-dimensional laser imaging radar is developed: Our system consists of a pulsed laser which is capable of generating 100mJ pulses with a pulse width of 10ns and a center wavelength of 532 nm, and a receiver which is a digital CCD sensor coupled to a GEN II intensifier with a 10nm bandwidth optical filter. The homogenized light beam passes through a diverging lens to flood illuminate the targets. The return light is collected by a Nikon camera lens and amplified by the image intensifier which is electronically driven and can be set to exponentially modulated gain or constant gain. The CCD sensor can record a 12 bit gray-level image with a resolution of 780×582 pixels at a 50 Hz frame rate. For a range image of the target can be extracted by processing an intensity image with exponentially modulated gain and an intensity image with constant gain, the range image is acquired at a 25 Hz frame rate. During our outdoor experiment, the range image of the targets at 500m is acquired with 2m range accuracy and the range image of the targets at about 1 kilometer is acquired with 5m range accuracy in daytime.