Technically, an isometric angle would be of 35.264 degrees from the horizontal, but this is avoided since the pixels created by a line drawing algorithm would not follow a neat pattern. To fix this, lines with a 1:2 pixel ratio are picked, leading to an angle of about 26.57 degrees (arctan 0.5). One subcategory is planometric, which is done at a 1:1 angle, giving a more top-down look. Another subcategory is "RPG perspective", in which the x and z (vertical) axes are combined into a side/top view. This view is facing an edge, instead of a vertex. Non-isometric pixel art is any pixel art that does not fall in the isometric category, such as views from the top, side, front, bottom or perspective views. When pixel art is displayed at a higher resolution than the source image, it is often scaled using the nearest-neighbor interpolation algorithm. This avoids blurring caused by other algorithms, such as bilinear and bicubic interpolation—which interpolate between adjacent pixels and work best on continuous tones, but not sharp edges or lines. Nearest-neighbor interpolation preserves these sharp edges, but it makes diagonal lines and curves look blocky, an effect called pixelation. Thus, hybrid algorithms have been devised to interpolate between continuous tones while preserving the sharpness of lines in the piece; such attempts include the 2xSaI, Super Eagle, and the high-quality hqx algorithms. Pixel art was very often used in older computer and console video games. With the increasing use of 3D graphics in games, pixel art lost some of its use. Despite that, there is still a very active professional/amateur community, since mobile phones and other portable devices still have low resolution and therefore require skillful use of space and memory. The improvement in current technology has caused pixel art to evolve, as it allows for better detail and animation in the art style than previously attainable. Pixel art has also been used in advertising, with one such company being Bell. The group eBoy specializes in isometric pixel graphics for advertising. Icons for operating systems with limited graphics abilities are also pixel art. The limited number of colors and resolution presents a challenge when attempting to convey complicated concepts and ideas in an efficient way. On the Microsoft Windows desktop icons are raster images of various sizes, the smaller of which are not necessarily scaled from the larger ones and could be considered pixel art.