Two techniques are devised for a natural image matting method using semi-supervised object extraction. One is a guiding scheme for placement of user strokes specifying object or background regions and the other is a scheme of adjustment of object colors for conforming to composited background colors. We draw strokes at inhomogeneous color regions disclosed with an unsupervised cluster extraction method from which the semi-supervised algorithm is derived. Objects are composited with a new background after their color adjustment using a color transfer method with eigencolor mapping. This image matting method is then extended to videos. Strokes are drawn only in the first frame from which memberships are propagated to successive frames to extract objects in every frame. Performance of the proposed method is examined with images and videos experimented with existing matting methods.