The first commercially successful color process, the Lumière Autochrome, invented by the French Lumière brothers, reached the market in 1907. Instead of colored strips, it was based on an irregular screen plate filter made of three colors of dyed grains of potato starch which were too small to be individually visible. The light-sensitive emulsion was coated directly onto the screen plate, eliminating problems due to imperfect contact between the screen and image. Reversal processing was used to convert the negative image which was initially produced into a positive image by removing the exposed silver metal, and re-exposing the remaining silver halide, so no printing or screen registration was required. The shortcomings of the Autochrome process were the expense (one plate cost about as much as a dozen black-and-white plates of the same size), the relatively long exposure times which made hand-held "snapshots" and photographs of moving subjects impractical, and the density of the finished image due to the presence of the light-absorbing color screen.