Jiqing Wu

Learned Collaborative Representations for Image Classification

The collaborative representation-based classifier (CRC) is proposed as an alternative to the sparse representation based classifier (SRC) for image face recognition. CRC solves an l2-regularized least squares formulation, with algebraic solution, while SRC optimizes over an I1-regularized least squares problem. As an extension of CRC, the weighted collaborative representation-based classifier (WCRC) is further proposed. The weights in WCRC are picked intuitively, it remains unclear why such choice of weights works and how we optimize those weights. In this paper, we propose a learned collaborative representation based classifier (LCRC) and attempt to answer the above questions. Our learning technique is based on the fixed point theorem and we use a weights formulation similar to WCRC as the starting point. Through extensive experiments on face datasets we show that the learning procedure is stable and convergent, and that LCRC is able to improve in performance over CRC and WCRC, while keeping the same computational efficiency at test.

Demosaicing Based on Directional Difference Regression and Efficient Regression Priors

Color demosaicing is a key image processing step aiming to reconstruct the missing pixels from a recorded raw image. On the one hand, numerous interpolation methods focusing on spatial-spectral correlations have been proved very efficient, whereas they yield a poor image quality and strong visible artifacts. On the other hand, optimization strategies, such as learned simultaneous sparse coding and sparsity and adaptive principal component analysis-based algorithms, were shown to greatly improve image quality compared with that delivered by interpolation methods, but unfortunately are computationally heavy. In this paper, we propose efficient regression priors as a novel, fast post-processing algorithm that learns the regression priors offline from training data. We also propose an independent efficient demosaicing algorithm based on directional difference regression, and introduce its enhanced version based on fused regression. We achieve an image quality comparable to that of the state-of-the-art methods for three benchmarks, while being order(s) of magnitude faster.

Efficient regression priors for post-processing demosaiced images

Color demosaicing is a process of reconstructing lost pixels in an incomplete color image. By extracting spatial-spectral correlations of RGB channels various interpolation methods have been proposed with low computational complexity. Meanwhile, optimization strategies such as sparsity and adaptive PCA based algorithm (SAPCA) were developed. SAPCA outperforms many interpolation techniques by impressive margins at the cost of dramatically increasing the computational time. In this paper we propose an efficient novel post-processing algorithm based on the adjusted anchored neighborhood regression (A+) method from image super-resolution literature. We greatly improve the results of the demosaicing methods, and achieve image quality as competitive as SAPCA but orders of magnitude faster.

Generic 3D Convolutional Fusion for Image Restoration

Also recently, exciting strides forward have been made in the area of image restoration, particularly for image denoising and single image super-resolution. Deep learning techniques contributed to this significantly. The top methods differ in their formulations and assumptions, so even if their average performance may be similar, some work better on certain image types and image regions than others. This complementarity motivated us to propose a novel 3D convolutional fusion (3DCF) method. Unlike other methods adapted to different tasks, our method uses the exact same convolutional network architecture to address both image denoising and single image super-resolution. Our 3DCF method achieves substantial improvements (0.1 dB–0.4 dB PSNR) over the state-of-the-art methods that it fuses on standard benchmarks for both tasks. At the same time, the method still is computationally efficient.

Wasserstein Divergence for GANs

In many domains of computer vision, generative adversarial networks (GANs) have achieved great success, among which the family of Wasserstein GANs (WGANs) is considered to be state-of-the-art due to the theoretical contributions and competitive qualitative performance. However, it is very challenging to approximate the k-Lipschitz constraint required by the Wasserstein-1 metric (W-met). In this paper, we propose a novel Wasserstein divergence (W-div), which is a relaxed version of W-met and does not require the k-Lipschitz constraint. As a concrete application, we introduce a Wasserstein divergence objective for GANs (WGAN-div), which can faithfully approximate W-div through optimization. Under various settings, including progressive growing training, we demonstrate the stability of the proposed WGAN-div owing to its theoretical and practical advantages over WGANs. Also, we study the quantitative and visual performance of WGAN-div on standard image synthesis benchmarks, showing the superior performance of WGAN-div compared to the state-of-the-art methods.