Securing color information of an image by concealing the color palette

This paper deals with a method to protect the color information of images by providing free access to the corresponding gray level images. Only with a secret key and the gray level images, it is then possible to view the images in color. The approach is based on a color reordering algorithm after a quantization step. Based on a layer scanning algorithm, the color reordering generates gray level images and makes it possible to embed the color palette into the gray level images using a data hiding algorithm. This work was carried out in the framework of a project aimed at providing limited access to the private digital painting database of the Louvre Museum in Paris, France.

► We propose to hide color information in a grey level image.
► We propose a color reordering algorithm (the layer scanning algorithm).
► We improve the gray-levels images by reducing the number of quantized colors.
► We analyze the results as a function of the number of colors, and as a function of the size of the layer.
► We compare our results with the approach of De Queiroz and Braun, and that of Campisi et al.