A Review On digital image processing techniques for in-Vivo confocal images of the cornea.

This work reviews the scientific literature regarding digital image processing for in vivo confocal microscopy images of the cornea. We present and discuss a selection of prominent techniques designed for semi- and automatic analysis of four areas of the cornea (epithelium, sub-basal nerve plexus, stroma and endothelium). The main context is image enhancement, detection of structures of interest, and quantification of clinical information. We have found that the preprocessing stage lacks of quantitative studies regarding the quality of the enhanced image, or its effects in subsequent steps of the image processing. Threshold values are widely used in the reviewed methods, although generally, they are selected empirically and manually. The image processing results are evaluated in many cases through comparison with gold standards not widely accepted. It is necessary to standardize values to be quantified in terms of sensitivity and specificity of methods. Most of the reviewed studies do not show an estimation of the computational cost of the image processing. We conclude that reliable, automatic, computer-assisted image analysis of the cornea is still an open issue, constituting an interesting and worthwhile area of research.

Influence of the occlusion effect over the prediction-error feedback cancellation system in hearing aids.

This work presents a theoretical analysis of the prediction-error method-based adaptive feedback canceller in hearing aid applications. The studied scene takes into account the occlusion effect caused by the partial or complete closing of the ventilation opening. Such a situation may occur in high gain applications to avoid undesired whistling. Deterministic recursive equations and steady-state conditions were derived for the mean weight behaviour of the predictor and the adaptive filter. The expected theoretical predictions were compared to Monte Carlo simulations, showing very accurate agreement. The simulation results suggest the steady-state performance of this feedback canceller is not affected by the occlusion effect, however the occlusion is still perceived, being annoying to the user.

A complementary low-cost method for broadband noise reduction in hearing aids for medium to high SNR levels.

This work presents a complementary broadband noise reduction scheme for hearing aid applications. It is designed to attenuate uncorrelated and small-correlation-length acoustic noise with controlled speech distortion. Noisy speech signals are pre-processed by the proposed strategy before being subjected to an existing narrowband noise reduction system. The clean speech signal is estimated by a convex combination of the unprocessed speech signal and the output of a linear predictor. The convex combination coefficient is adjusted to provide noise suppression while avoiding significant unvoiced utterance distortions. The proposed method is optimized to minimize speech mean-square prediction-error. A low-cost adaptive implementation is proposed and compared to the conventional adaptive linear predictor showing an improved performance, as predicted by theory. Four different objective quality measures and subjective assessment performed by normal hearing volunteers indicate that the combined use of the proposed technique with a narrowband noise reduction system consistently improves speech quality for a range of signal to noise ratios. Low-cost digital hearing aids that make use of the conventional adaptive predictor for broadband noise reduction can be easily modified to incorporate the new proposal with a minimum amount of extra computational resources.