use of the Quattro sensor, a variant of the Foveon design that has a higher resolution top layer and lower resolution lower layers combined into a final image that is claimed to be equivalent to a 39 megapixel color filter array image. The four compact cameras are differentiated by their fixed prime lens, with the ultra wide DP0, the wide DP1, the normal DP2 and the telephoto DP3. In February 2016, Sigma announced two new mirrorless cameras—the SD Quattro and SD Quattro H. Both cameras use the full-depth Sigma SA mount, allowing the use of existing SA-mount lenses, and also use Foveon Quattro sensors. The SD Quattro uses an APS-C sensor with 19.6 MP in the top layer, while the SD Quattro H uses an APS-H (1.35x crop) sensor with 25.5 MP in the top layer. The company claims that the Foveon Quattro technology produces a level of detail equivalent to that of a Bayer sensor with twice the pixel count. Software Sigma produces the Sigma Photo Pro software for post-production of their camera's .X3F raw image format. It is available both for Mac OS and Microsoft Windows. Lenses Sigma makes autofocus lenses for the Sigma SA, Canon EF, Nikon F, Minolta/Sony α, Pentax K and Four Thirds lens mounts. Each lens may not be available in all mounts, and may lack certain features (such as HSM) on certain mounts. In August 2013, Sigma announced that starting the following month, it would offer a mount conversion service for its newest "Global Vision" lenses—those with either an "A" (Art), "C" (Contemporary), or "S" (Sport) as part of their model name. For a cost that varies with lens and market—from $80 to $250 in the U.S., not including shipping costs—owners can send their lenses to their local Sigma company, which in turn sends them to Japan for mount replacement, including calibration and optimization for the new camera system. Lenses designed for DSLRs can be converted to Canon EF, Nikon F, Pentax K, Sigma SA, or Sony A mounts; those designed for MILCs can be converted to Micro Four Thirds or Sony E-mount. Designations ASP — Aspherical lens elements APO — Apochromatic lens element(s), originally for "Advanced Performance Optics", not necessarily apochromatic OS — In-lens "Optical Stabilization", analogous to Nikon VR or Canon IS HSM — "Hyper-Sonic Motor", either in-lens ultrasonic motor or micro-motor, analogous to Nikon SWM (AF-S) (ultra-sonic or micro-motor), Canon