Adaptive Colour Filter Array (CFA) Demosaicking with Mixed Order of Approximation

The estimation of missing pixel colour values when using a single-sensor digital camera for full colour image capture is known as colour filter array (CFA) demosaicking. It has recently been shown that missing colour values can be approximated using Taylor series with good accuracy. In order to prevent the appearance of colour artefacts around an edge boundary, it is desirable to avoid interpolation across an edge. By the application of an edge direction map, we can determine the preferred direction for interpolation, either vertically or horizontally for the green plane. In this paper, interpolation is carried out along a preferred direction and samples from both sides of the missing colour value are used. The order of approximation for the estimates on each side of the missing colour value is determined independently and adoptively depending on whether there is a nearby edge and its distance from the missing colour value. For example, if a colour edge is nearby, a lower order of approximation, which only uses samples close to the missing colour value, will be employed so as to avoid the inclusion of the colour edge. However, if a colour edge is further away on the other side of the missing colour value, a higher order of approximation for higher accuracy will be used instead. The missing colour value is then estimated by combining the estimates from both sides with their respective orders of approximation. This proposed method using mixed order of approximation has been shown to produce better performance than the method by selecting a single estimate as the output.