  Transformations for enhancing sparsity in the approximation of color images
by 2D atomic decomposition are discussed. The sparsity is firstly considered
with respect to the most significant coefficients in the wavelet decomposition
of the color image. The discrete cosine transform is singled out as an
effective transformation for this purpose. The enhanced feature is further
exploited by approximating the transformed arrays using an effective greedy
strategy with a separable highly redundant dictionary. The relevance of the
achieved sparsity is illustrated by a simple encoding procedure. On a set of
typical test images the compression at high quality recovery is shown to
significantly improve upon JPEG and WebP formats. The results are competitive
with those produced by the JPEG2000 standard.
