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In computing, half precision is a binary floating-point computer number format that occupies 16 bits (two bytes in modern computers) in computer memory. In IEEE 754-2008 the 16-bit base 2 format is officially referred to as binary16. It is intended for storage (of many floating-point values where higher precision need not be stored), not for performing arithmetic computations. Half-precision floating point is a relatively new binary floating-point format. Nvidia defined the half datatype in the Cg language, released in early 2002, and was the first to implement 16-bit floating point in silicon, with the GeForce FX, released in late 2002.〔Nvidia〕 ILM was searching for an image format that could handle a wide dynamic range, but without the hard drive and memory cost of floating-point representations that are commonly used for floating-point computation (single and double precision).〔http://www.openexr.com/about.html〕 The hardware-accelerated programmable shading group led by John Airey at SGI (Silicon Graphics) invented the s10e5 data type in 1997 as part of the 'bali' design effort. This is described in a SIGGRAPH 2000 paper〔http://people.csail.mit.edu/ericchan/bib/pdf/p425-peercy.pdf〕 (see section 4.3) and further documented in US patent 7518615.〔http://www.google.com/patents/US7518615〕 This format is used in several computer graphics environments including OpenEXR, JPEG XR, OpenGL, Cg, and D3DX. The advantage over 8-bit or 16-bit binary integers is that the increased dynamic range allows for more detail to be preserved in highlights and shadows for images. The advantage over 32-bit single-precision binary formats is that it requires half the storage and bandwidth (at the expense of precision and range).〔 == IEEE 754 half-precision binary floating-point format: binary16 == The IEEE 754 standard specifies a binary16 as having the following format: * Sign bit: 1 bit * Exponent width: 5 bits * Significand precision: 11 bits (10 explicitly stored) The format is laid out as follows: The format is assumed to have an implicit lead bit with value 1 unless the exponent field is stored with all zeros. Thus only 10 bits of the significand appear in the memory format but the total precision is 11 bits. In IEEE 754 parlance, there are 10 bits of significand, but there are 11 bits of significand precision (log10(211) ≈ 3.311 decimal digits). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Half-precision floating-point format」の詳細全文を読む スポンサード リンク
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