Image matting is the process of extracting a foreground element from a single image with limited user input. To solve the inherently ill-posed problem, there exist various methods which use specific color model. One representative method assumes that the colors of the foreground and background elements satisfy the linear color model. The other recent method considers line-point color model and point-point color model. In this paper we present a new adaptive color curve model for image matting. We assume that the colors of local region form curve. Based on these pixels in the local region, we adaptively construct a curve model using quadratic Bézier curve model. This curve model enables us to derive a matting equation for estimating alphas of pixels forming a curve using quadratic formula. We show that our model estimates alpha mattes comparable or more accurately than recent existing methods.