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Papers by Birgitta Martinkauppi

IFAC Proceedings Volumes, Aug 1, 2013

Pattern Recognition, 2003

SPIE Proceedings, 1999

Saturation here refers to electronic saturation of the camera sensors which produces clipped colo... more Saturation here refers to electronic saturation of the camera sensors which produces clipped colors, and not the purity of color as in the hue-saturation and value scale. Saturated images are routinely discarded in image analysis yet there are situations when they cannot be avoided. This paper proposes two strategies to recover color information in facial images taken under non-ideal conditions to make them useful for further processing. The first assumes that the skin is matte and that there are parts of the image which are not clipped. Ratios between R,G and B values of unclipped pixels belonging to the same parts of the image may then be used to compute for lost channel values. The second approach uses color eigenfaces computed from our physics-based face database obtained under different illuminants and camera calibration conditions. Skin color is recovered by transforming the first few eigenface coefficients towards ideal condition values. Excellent color recovery for clipped images is achieved when these two techniques are combined and used on face images captured under daylight illuminant with a camera white balanced for incandescent light.

SPIE Proceedings, 2001

The appearance of skin colors in the images depends among other things, on the camera, the calibr... more The appearance of skin colors in the images depends among other things, on the camera, the calibration of the camera, and the illumination under which the image was taken. In this study, we investigate how the skin colors appear in the chromaticity coordinates of different color spaces like HSV/HSL, normalized rgb, YES and TSL. For this purpose, we have taken images of faces under 16 different illumination/camera calibration conditions using simulated illuminants (Horizon, A, fluorescent TL84 and daylight) with different RGB cameras (1CCD web cameras and a 3CCD camera). In the making of this series of 16 images, first the selected camera was calibrated to one of the four light sources and an image was taken. After that the light source was changed to the other light sources and at each time the person was imaged. The process was repeated to the other two light sources. The same procedure was done for all four light sources and for each cameras. The skin regions were extracted from these images and this skin data was then converted to different color spaces. We inspected how the chromaticities of different skin color groups in these color spaces overlap in images taken in all 16 different cases and only in those cases in which the selected camera was calibrated to the current illuminant. These investigations were also made between different cameras. In addition to this, we examined the overlapping of all skin chromaticities from the different skin color groups between cameras.

Decentralized energy production and markets for renewable energy technologies are continually exp... more Decentralized energy production and markets for renewable energy technologies are continually expanding. The market growth is ensured, for example, by international and EU policies for renewable energy generation, the EU directives for increasing competition within the electricity industry and the rising prices of fossil fuels. Local energy production increases energy efficiency because of lower transport or transfer losses. Local energy production also increases local business and energy production from local waste reduces waste management costs, thus enabling other local business and local employment. Local energy production also increases energy, electricity and fuel security by reducing import dependency. Combining together different technologies can form a strong hybrid solution adapted to local needs. Here the technologies interconnect and work in symbiosis supporting each other so that, in some cases, waste from one process is raw material or fuel for another. By combining the technological solutions for local needs, high primary energy efficiency can be achieved, thereby ensuring that local energy production potential is fully realized. Possibilities and new solutions based on energy saving and the use of local energy sources were studied in a single-family house. The annual energy consumption of space heating and ventilation in the climate of Southern Finland is approximately 50 kWh/m 2 calculated per floor area. With an extremely well insulated envelope and effective heat recovery from exhaust air, it is possible to achieve the passive house level of 15 kWh/m 2. However, this is an expensive way because usually improvements in HVAC systems are more cost-effective than constantly improving the thermal insulation of the envelope from the Finnish reference values of the year 2012. The net zero energy level is difficult to reach because of heating of hot water, if you do not also build solar heating system for heating or warm waste water recovery system. A ground heat pump system offers a possibility to reduce the electricity consumption of heating, including also the heating of hot water, of a new single-family house to the level of 30-40 kWh/m 2. With an exterior air heat pump and solar water heating, the corresponding energy consumption is 35-60 kWh/m 2. The net zero-energy building resulted in lower environmental impacts than the other cases (district heating and electricity) in all other environmental impact categories except for eutrophication impacts. The high eutrophication impacts are caused by the high phosphorus emissions resulting from the solar panel manufacturing. In the other impacts studied, those caused by the net-zero energy house were only approximately. 50% or less of those caused by the other two cases. The difference between Cases 2 and 3 was very small, although impacts were caused by different processes in the two cases. The cost efficiency of the measures studied, investment cost/annual energy saving, is 0.4-4.8 €/kWh. Generally the investments in heating and heat recovery

International Journal of Spectroscopy, 2013

This paper is a review of optical methods for online nondestructive food quality monitoring. The ... more This paper is a review of optical methods for online nondestructive food quality monitoring. The key spectral areas are the visual and near-infrared wavelengths. We have collected the information of over 260 papers published mainly during the last 20 years. Many of them use an analysis method called chemometrics which is shortly described in the paper. The main goal of this paper is to provide a general view of work done according to different FAO food classes. Hopefully using optical VIS/NIR spectroscopy gives an idea of how to better meet market and consumer needs for high-quality food stuff.

The colours of objects perceived by a colour camera are dependent on the illumination conditions.... more The colours of objects perceived by a colour camera are dependent on the illumination conditions. For example, when the prevailing illumination condition does not correspond to the one used in the white balancing of the camera, the object colours can change their appearance due to the lack of colour constancy capabilities. Many methods for colour constancy have been suggested but so far their performance has been inadequate. Faces are common and important objects encountered in many applications. Therefore, this thesis is dedicated to studying face colours and their robust use under real world illumination conditions. The main thesis statement is "knowledge about an object's colour, like skin colour changes under different illumination conditions, can be used to develop more robust techniques against illumination changes". Many face databases exist, and in some cases they contain colour images and even videos. However, from the point of view of this thesis these databases have several limitations: unavailability of spectral data related to image acquisition, undefined illumination conditions of the acquisition, and if illumination change is present it often means only change in illumination direction. To overcome these limitations, two databases, a Physics-Based Face Database and a Face Video Database were created. In addition to the images, the Physics-Based Face Database consists of spectral data part including skin reflectances, channel responsivities of the camera and spectral power distribution of the illumination. The images of faces are taken under four known light sources with different white balancing illumination conditions for over 100 persons. In addition to videos, the Face Video Database has spectral reflectances of skin for selected persons and images taken with the same measurement arrangement as in the Physics-Based Face Database. The images and videos are taken with several cameras. The databases were used to gather information about skin chromaticities and to provide test material. The skin RGB from images were converted to different colour spaces and the result showed that the normalized colour coordinate was among the most usable colour spaces for skin chromaticity modelling. None of the colour spaces could eliminate the colour shifts in chromaticity. The obtained chromaticity constraint can be implemented as an adaptive skin colour modelling part of face tracking algorithms, like histogram backprojection or mean shift. The performances of these adaptive algorithms were superior compared to those using a fixed skin colour model or model adaptation based on spatial pixel selection. Of course, there are cases when the colour cue is not enough alone and use of other cues like motion or edge data would improve the result. It was also demonstrated that the skin colour model can be used to segment faces and the segmentation results depend on the background due to the method used. Also an application for colour correction using principal component analysis and a simplified dichromatic reflection model was shown to improve colour quality of seriously clipped images. The results of tracking, segmentation and colour correction experiments using the collected data validate the thesis statement.