Enhancement of Learning Based Image Matting Method with Different Background/Foreground Weights

The problem of accurate foreground estimation in images is called Image Matting. In image matting methods, a map is used as learning data, which is produced by those pixels that are definitely foreground, definitely background ,and unknown. This three-level pixel map is often referred to as a trimap, which is produced manually in alpha matte datasets. The true class of unknown pixels will be estimated by minimizing of an objective function. Several methods for image matting has been proposed. The learning–based method is one the pioneering works which is the basis of many other approaches in the field of image matting.  In this method it is assumed that each pixel’s alpha value is a linear combination of its associated neighboring pixels. A Laplacian matrix in the objective function shows the similarity of the pixels. The coefficients of the linear combination are estimated with a local learning process by minimizing a quadratic cost function. The method of Lagrange multiplier and ridge regression technique are used for estimation of alpha values. In this objective function the violation of the predefined training pixels’ alpha values from their true values is controlled by a penalty term. Considering this coefficient as infinity, forces the matte (alpha) value to be 1 for the labeled foreground pixels and 0 for background. The weight of this penalty term still was taken equal for all training samples. In this paper the performance of the matting method is increased by considering different weights for different learning pixels. The good performance of the proposed method is demonstrated in two applications. The first application is improving the quality of a text extraction method and the second application is enhancement of an eye retinal segmentation system. In the first application, a Persian text which is fused onto a textured background is extracted by a thresholding method. After that the segmented output is enhanced by the proposed matting method. In the second application, segmentation is done with an existing vessel extraction method. The edges’ pixels of detected vessels that may be classified inaccurately are classified by the proposed image matting method. Subjective and objective comparisons show the better performance of the proposed method.