Avoiding oddification to simplify MPEG-1 decoding with LNS

M. Arnold
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引用次数: 3

Abstract

Low-precision logarithmic number system (LNS) arithmetic can reduce the power consumption for MPEG decoding compared to conventional fixed-point techniques. Although this introduces small numeric errors, which violate the IEEE-1180 standard for the inverse discrete cosine transform (IDCT), the visual effects of such error may be tolerable for portable battery-powered devices, like videophones, that have limited-resolution displays. The MPEG standard achieves video compression by quantization of the data fed to the IDCT. The MPEG decoder must multiply this data by dequantization factors. Such multiplication, by itself, is trivial with LNS since adding logarithms is equivalent to multiplication. The IEEE-1180 standard suggests oddification, where fixed-point data is forced to become odd after dequantization to minimize IDCT mismatch between the encoder and the decoder. Oddification poses an implementation problem for data in LNS format. This paper suggests that the visual effect of LNS without oddification is nearly indistinguishable from LNS with oddification, meaning that the benefits of LNS in MPEG are even greater than previously expected.
避免修改,简化LNS的MPEG-1解码
与传统的定点解码技术相比,低精度对数系统(LNS)算法可以降低MPEG解码的功耗。虽然这会引入小的数值误差,这违反了IEEE-1180的反离散余弦变换(IDCT)标准,但对于具有有限分辨率显示的便携式电池供电设备(如可视电话),这种误差的视觉效果可能是可以容忍的。MPEG标准通过对送入IDCT的数据进行量化来实现视频压缩。MPEG解码器必须将这些数据乘以去量化因子。这种乘法本身对于LNS来说是微不足道的,因为添加对数等同于乘法。IEEE-1180标准建议进行奇数化,即定点数据在去量化后强制变为奇数,以最小化编码器和解码器之间的IDCT不匹配。修改对LNS格式的数据造成了实现上的问题。本文认为,无修饰的LNS与有修饰的LNS的视觉效果几乎没有区别,这意味着LNS在MPEG中的好处甚至比之前预期的要大。
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