Vittoria Bruni

A generalized model for scratch detection

This paper presents a generalization of Kokarams model for scratch lines detection on digital film materials. It is based on the assumption that scratch is not purely additive on a given image but shows also a destroying effect. This result allows us to design a more efficacious scratch detector which performs on a hierarchical representation of a degraded image, i.e., on its cross section local extrema. Thanks to Webers law, the proposed detector even works well on slight scratches resulting completely automatic, except for the scratch color (black or white). The experimental results show that the proposed detector works better in terms of good detection and false alarms rejection with a lower computing time.

Wavelet-based signal de-noising via simple singularities approximation

In this paper WISDOW (wavelet-based image and signal de-noising via overlapping waves) is presented. It consists of a novel model for noise removal using wavelets. Its main peculiarity is the modelling of a noisy signal as composition of elementary atoms which behave as interfering waves in the wavelet domain. Signal recovery is then performed by means of the overlapping effects principle at each scale level. Early theoretical and experimental results show the great potential of the proposed model.

Combined image compression and denoising using wavelets

This paper presents a novel scheme for simultaneous compression and denoising of images: WISDOW-Comp (Wavelet based Image and Signal Denoising via Overlapping Waves-Compression). It is based on the atomic representation of wavelet details employed in WISDOW for image denoising. However, atoms can be also used for achieving compression. In particular, the core of WISDOW-Comp consists of recovering wavelet details, i.e. atoms, by exploiting wavelet low frequency information. Therefore, just the approximation band and significance map of atoms absolute maxima have to be encoded and sent to the decoder for recovering a cleaner as well as compressed version of the image under study. Experimental results show that WISDOW-Comp outperforms the state of the art of compression based denoisers in terms of both rate and distortion. Some technical devices will also be investigated for further improving its performances.

A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.

Fast removal of line scratches in old movies

In this paper a fast algorithm for removing line scratches in old movies is presented. It is strongly based on exploiting the defect visibility in the image. To this aim the Webers law can be applied to coefficients of an over-complete wavelet representation of the degraded image. The intensity of the defect, which is represented as a light diffraction effect, is then attenuated in the vertical and approximation sub-bands till the minimum threshold of visibility is reached. The experimental results are very satisfying: the image is completely recovered without local artifacts or annoying smoothing effects.

On the Equivalence Between Jensen–Shannon Divergence and Michelson Contrast

This paper focuses on the link between a visible linear and local distortion in a pictorial scene and its cost in terms of information theory quantities. In particular, a formal relation between the Michelson visual contrast and the Jensen-Shannon divergence (JSD) will be provided. A universal just noticeable threshold is also derived by maximizing JSD constrained to the greatest Michelson contrast of an invisible distortion. Such a threshold is independent of both distortion parameters and the probability density function of the degraded image. It is then able to measure the bits budget to be spent for leaving the distortion invisible. Some tests on both synthetic and real distorted images validate the theoretical findings. They confirm that the proposed universal threshold is really able to get the lower bound of human perception and then it may be useful for many applications, such as bit allocation in coding procedures and automatic parameters setting in restoration algorithms.

Semi-transparent blotches removal from sepia images exploiting visibility laws

This paper presents a novel model for the removal of semi-transparent blotches on the digitized copy of sepia archive photographs. As these defects cannot be successfully eliminated by conventional interpolation methods, a proper combination of a novel visual distortion and multiresolution analysis is used for performing user-independent detection and restoration. Extensive experimental results and comparative studies show the potential of the proposed model in terms of visual quality and computational complexity.

Jensen–Shannon divergence for visual quality assessment

This paper focuses on some theoretical properties of the Jensen–Shannon divergence (JSD) that well match human visual system (HVS) features. In particular, it is firstly shown that JSD between the probability density function (pdf) of the reference (original) image and the test (distorted) one can be reformulated as a mathematical expansion, independently of the image subject and the distortion kind. Such expansion contains a component of the well-known structural similarity measure (SSIM), some powers of the Weber’s law, and an additional component tied to the skewness of the involved pdfs. This theoretical link with some HVS-based quantities is further stressed by some experimental results showing that JSD has a trend similar to other popular quality assessment measures like SSIM, VIF, and MSE on frequent degradation kinds like JPEG, Additive Gaussian Noise, Gaussian Blur, and JPEG2K. Experimental tests on several images from LIVE database show that the proposed approach can be a valid theoretical and objective support for modeling HVS behavior.

A Wiener filter improvement combining wavelet domains

An improvement of an interesting approach for denoising in the wavelet domain using an empirical Wiener filter (Choi, H. and Baraniuk, R., Proc. IEEE-SP Int. Symp. on Time-frequency and Time-scale Anal., 1998) is presented. It is based on a well-balanced matching of selection and attenuation performances using more than one wavelet basis. Experimental results are better than other wavelet-Wiener based techniques, both in terms of objective (signal-to-noise ratio, SNR) and subjective quality, requiring a moderate computing time.

An Improvement of Kernel-Based Object Tracking Based on Human Perception

The objective of the paper is to embed perception rules into the kernel-based target tracking algorithm and to evaluate to what extent these rules are able to improve the original tracking algorithm, without any additional computational cost. To this aim, the target is represented through features that are related to its visual appearance; then, it is tracked in subsequent frames using a metric that, again, correlates well with the human visual perception (HVP). The use of HVP rules are twofold advantageous: it allows us to both increase tracking efficacy and considerably reduce the computational cost of the tracking process-thanks to the reduced size of the perceptual feature space. Various tests on video sequences have shown the stability and the robustness of the proposed framework, also in the presence of both other moving objects and partial or complete target occlusion in a limited number of subsequent frames.