There are two different categories of methods for producing vector gradients. One is mainly interested in converting existing photographs into dense vector representations. By vector it is meant that one can zoom infinitely inside images, and that control values do not have to lie onto a grid but must represent subtle color gradients found in input images. The other category is tailored to the creation of images from scratch, using a sparse set of vector primitives. In this case, we still have the infinite zoom property, but also an advanced model of how space should be filled in-between primitives, since there is no input photograph to rely on. These two categories are actually extreme cases, and seem to exclude each other: a dense representation is difficult to manipulate, especially when one wants to modify topology; a sparse representation is hardly adapted to photo vectorization, especially in the presence of texture. Very few methods lie in the middle, and the ones that do require user assistance. The challenge is worth the effort though: it would permit to convert an image into a vector primitives easily amenable to stylization.