Rob Anne Beuker

Compensation of crosstalk of chrominance coding errors into the luminance

Component-based color video signals usually consist of one luminance (Y) and two chrominance or color-difference (U and V) components, which are obtained by multiplying the R, G and B components produced by the video camera by a 3 X 3 matrix. In order to compensate for the nonlinearity of the TV monitor on which the video signal will be displayed, the R, G, and B signals are usually first gamma-corrected before the matrix operation is applied. Due to this gamma correction, the Y component does not represent exactly the real luminance L of the recorded scene, and part of the real luminance information is carried by the U and V components. The introduction of errors into these chrominance components by, for example, video coding will therefore lead to perceivable errors in the luminance produced by the TV monitor on which the coded signal is eventually displayed. In this paper, we present a simple but effective method for avoiding this crosstalk of chrominance errors into the luminance. This method can be incorporated in most compression systems.

Perceptually relevant model for aliasing in the triplet-stripe filter CCD image sensor

Abstract In this paper we present a signal-theoretical model of the aliasing in the triplet stripe filter CCD image seli-sor. In this sensor, the colour filters are placed in a repetitive pattern of three columns on the monochromesensor. Therefore the projected scene is sampled at every three columns and aliasing can result. We usethe signal-theoretical model to predict the visibility of the aliasing. 1 Introduction Colour cameras with one CCD (Charge Coupled Device) image sensor are widely used. A CCD imagesensor consists of a matrix of light sensitive pixels (see Fig. 1). This device is a monochrome image sensor. iiiii xo Figure 1: A front view of a CCD image sensor, which is an array of light sensitive pixelsTo use it as a colour image sensor, colour filters are placed on top of the light sensitive pixels. In this paperwe will consider a special placement of the colour filters, namely the triplet stripe filter. The colour filtersare placed as stripes on top of the columns in a repetative pattern of three columns (see Fig. 2).The colour filters sample the light, which is projected on the sensor. Suppose the sensor has red, greenand blue colour filters. Since the green and blue colour filters do not transmit red light, a red scene givesan output from columns one, four, seven, etc. of the CCD. If high spatial frequencies are not suppressedby optical filters, aliasing results. An Optical Low-Pass ifiter (OLP), which is not ideal, is used to reducethe high frequency content (see Fig. 3). The aliasing is visible as blockiness and colour errors.