# Highly Nonlinear Approximations for Sparse Signal Representation

## Application to Image Folding

In order to apply the embedding scheme to fold an image we simply process the image by dividing it into, say blocks, of pixels. We find the representation of each block with a combination of discrete cosine and spline based subdictionaries constructed as explained in [35]. With this dictionaries the image of Fig 10 has a highly sparse representation at PSNR=40 dB (the CR is approximately 11) so that we are able to store the whole image embedding the few pixels shown in the top picture of Fig 10. The next picture is the unfolded image without using the security*key*and the right picture the one obtained with the correct

*key*. For further implementation details see [33]. An example of how to call the available codes for sparse image approximation with cosine and spline based dictionaries can be found here.