Résumé
In this paper, we propose a method to embed the color information of an image in a corresponding grey-level image. The objective of this work is to allow free access to the grey-level image and give color image access only if you own a secret key. This method is made of three major steps which are the color quantization, the ordering and the data hiding. The originality of this paper is to build an {\em indexed image} which is, in the same time, a semantically intelligible grey-level image. In order to obtain this particular {\em indexed image}, which should be robust to data hiding, we propose an original $K$ color ordering algorithm called the {\em layer running algorithm}.