Jukka Yrjänäinen

Wireless meets multimedia - New products and services

Mobile person to person speech communication has turned out to be extremely popular with more than one billion users today. Currently, mobile networks are evolving to support multimedia communications. In coming years, access to various sources of multimedia will further enrich mobile communication. New mobile phones, with graphical color displays and integrated cameras, will provide a natural platform for a large set of multimedia applications. Open software architectures in these terminals are giving new possibilities to the developer community. Evolution of the mobile multimedia will create new challenges and opportunities for related research and development activities.

Adaptive outlier rejection in image super-resolution

One critical aspect to achieve efficient implementations of image super-resolution is the need for accurate subpixel registration of the input images. The overall performance of super-resolution algorithms is particularly degraded in the presence of persistent outliers, for which registration has failed. To enhance the robustness of processing against this problem, we propose in this paper an integrated adaptive filtering method to reject the outlier image regions. In the process of combining the gradient images due to each low-resolution image, we use adaptive FIR filtering. The coefficients of the FIR filter are updated using the LMS algorithm, which automatically isolates the outlier image regions by decreasing the corresponding coefficients. The adaptation criterion of the LMS estimator is the error between the median of the samples from the LR images and the output of the FIR filter. Through simulated experiments on synthetic images and on real camera images, we show that the proposed technique performs well in the presence of motion outliers. This relatively simple and fast mechanism enables to add robustness in practical implementations of image super-resolution, while still being effective against Gaussian noise in the image formation model.

Wireless meets multimedia

Mobile person-to-person speech communication has turned out to be extremely popular with more than one billion users today. Currently, mobile networks are evolving to support efficient and flexible data communications. This development will also enable an efficient use of multimedia elements in mobile communication. New content types, applications and services are emerging. Multimedia Messaging Service (MMS) is one key element in this development. From the user point of view, it is the continuation of a very popular mobile messaging paradigm and it offers a framework for mobile person-to-person multimedia communication. New mobile phones, with graphical color displays and integrated cameras, will provide a natural platform for a large set of multimedia applications. Including multimedia capabilities for small portable devices is driving the new development on display, imaging and processor technologies. Open software architectures in these terminals are giving new possibilities to the developer community. Evolution of the mobile multimedia will create new challenges and opportunities for related research and development activities. Copyright

43.1: Image Enhancement for Reflective Displays

The reflective and transflective LCD technologies offer attractive solutions for color displays that are used in handheld devices. These technologies make possible to obtain a full color display with low power consumption by using ambient illumination as light source. When there is not enough ambient light an internal light source can be used. The current generation of displays has quite adequate quality for viewing color images in some conditions, but they still have also some insufficient properties. The color gamuts and contrast ratio of the displays are small and dependent on the illumination. We have researched how the properties of the displays affect imaging applications and how those can be overcome by using image processing means. We are focusing on image enhancement algorithms, which we have tested under different viewing conditions. Especially algorithms that are effectively implementable are interesting. In this case the target is to increase the visibility and the subjective quality of the image on the display as opposed to reproduce the originally intended appearance exactly. The achieved results show that the perceived image quality and the usability of the display can be enhanced significantly using image enhancement techniques.

Order filters in superresolution image reconstruction

In this paper, we propose the use of order filters in the iterative process of super-resolution reconstruction. At each iteration, order statistic filters are used to filter and fuse the error images. The signal dependent L-filter structure adjusts its coefficients to achieve edge preservation as well as maximum noise suppression in homogeneous regions. Depending on the amount of variance of the image pixels in different directional masks, the filter switches to use the orientation, which is most likely to follow the image edges. This procedure allows for the incorporation of a directional prior across the iterations. The introduction of a spatial filtering stage into the iterative process of super-resolution attempts to increase the robustness towards motion error and image outliers. Experimental results show the improvement obtained on sequences of noisy text images when motion is exactly known, and when a random motion error is introduced to simulate the real life situation of inaccurate motion estimation.

A Method for Simultaneous Outlier Rejection in Image Super-Resolution

In this paper, we propose a method to adaptively reject outlier image regions in the process of super-resolution image reconstruction. We use adaptive FIR filtering while iteratively fusing the gradient images. The LMS adapted filter coefficients automatically isolate the outlier image regions, for which motion was inaccurately estimated. The adaptation criterion used is the median of the errors at each pixel location. Through simulated experiments on synthetic images, we show that the proposed technique performs well in the presence of outlier images. This relatively simple and fast mechanism enables to add robustness in practical implementations of super-resolution, while still effective against Gaussian noise.