Lv驱动库底层实际使用 Q8定点及其定点实现

目录一、定点化二、数据节点规划三、Lv Q8定点计算代码实现四、数据线性插值ISP Pipeline中Lv实现方式探究之一ISP Pipeline中Lv实现方式探究之二ISP Pipeline中Lv实现方式探究之三--lv计算定点实现ISP Pipeline中Lv实现方式探究之四----正LV值定点实现一、定点化如上博文都是讲解了Lv计算的基本原理。实际在ISP驱动中该如何根据上述原理进行Lv值的计算呢LV log₂(1/(T·Gain)) Lv_Offset其中T表示秒为单位的曝光时间Gain为总的增益倍数Lv_offset8LV计算定点化之前的公式ISP驱动库内部对应的增益倍数也不能使用小数LV在ISP驱动块中显然也不能使用浮点数。因此都需要做相应的定点化处理。假设都做Q8得定点化处理。即上式改写为LV log2(X) - log2(A_Q8 /256) - log2(D_Q8/256) - log2(I_Q8/256) 8LV log2(X) - ( log2(A_Q8) - 8 ) - ( log2(D_Q8) - 8 ) - ( log2(I_Q8) - 8 ) 8LV log2(X) - log2(A_Q8) - log2(D_Q8) - log2(I_Q8) 32LV_Q8 log2X_Q8 - log2A_Q8 - log2D_Q8 - log2I_Q8 32*256二、数据节点规划曝光时间节点划分为1/512,1/256,1/128,1/64,1/32,1/16,1/8,1/4秒支持最低帧率5帧支持最小曝光时间为1/5120.001953125s。小于1/512即为较亮场景的可以直接限制为1/512s。增益节点划分一般普通的sensor模拟增益相对较大数字增益倍数相对较小。我们以模拟增益128倍为增益节点的上限。以1X,2X,4X,8X,16X,32X,64X,128X为增益节点。由于增益是按照总的增益倍数因此我们只需要支持最大模拟增益即可数字增益和ISP增益倍数一般都小于128倍。总的增益可以支持512X当时单个增益最大倍数为128X。三、Lv Q8定点计算代码实现3.1 迭代版本1考虑到LV_Q8 log2X_Q8 - log2A_Q8 - log2D_Q8 - log2I_Q8 32*256公式中X最大值为512即规划一个计算好的log2对数Q8定点查找表实现曝光时间的计算。这样同时也能够计算2倍增益Q8定点数据。考虑到大于2X增益的计算使用二项多项式拟合定点计算计算得到。具体实现实例代码为//使用二阶多项式拟合log2函数 // 固定配置 #define Q8 256 // Q8 定点格式 #define LV_OFFSET (32 * Q8) // 固定偏移 32 #define MAX_INPUT 512 // X/A/D/I 最大值 #define MIN_X 4 // 曝光 X 最小值4 #define MAX_GAIN (128*Q8) uint16_t log2_x256_fast(uint16_t x) { uint8_t k; // 处理 f2.0 越界问题 if (x 32768) { return 3840; } if (x 16384) k 14; else if (x 8192) k 13; else if (x 4096) k 12; else if (x 2048) k 11; else if (x 1024) k 10; else k 9; // 归一化到 [256, 512] Q8 uint16_t f_q8 (k 15) ? 512 : (x (k - 8)); int16_t d f_q8 - 256; int16_t d2 (int16_t)(((int32_t)d * d) 8); // 二阶多项式高精度近似 int32_t logf_q8 ((int32_t)d * 369 8) - ((int32_t)d2 * 185 8); // 最终 Q8 结果 return (uint16_t)((k 8) logf_q8); } // // log2(x) Q8 查表 (0~512) // const uint16_t log2_q8_lut[MAX_INPUT 1] { 0, 0, 256, 406, 512, 594, 662, 719, 768, 812, 850, 886, 918, 947, 975, 1000, 1024, 1046, 1068, 1087, 1106, 1124, 1142, 1158, 1174, 1189, 1203, 1217, 1231, 1244, 1256, 1268, 1280, 1291, 1302, 1313, 1324, 1334, 1343, 1353, 1362, 1372, 1380, 1389, 1398, 1406, 1414, 1422, 1430, 1437, 1445, 1452, 1459, 1466, 1473, 1480, 1487, 1493, 1500, 1506, 1512, 1518, 1524, 1530, 1536, 1542, 1547, 1553, 1558, 1564, 1569, 1574, 1580, 1585, 1590, 1595, 1599, 1604, 1609, 1614, 1618, 1623, 1628, 1632, 1636, 1641, 1645, 1649, 1654, 1658, 1662, 1666, 1670, 1674, 1678, 1682, 1686, 1690, 1693, 1697, 1701, 1705, 1708, 1712, 1715, 1719, 1722, 1726, 1729, 1733, 1736, 1739, 1743, 1746, 1749, 1752, 1756, 1759, 1762, 1765, 1768, 1771, 1774, 1777, 1780, 1783, 1786, 1789, 1792, 1795, 1798, 1801, 1803, 1806, 1809, 1812, 1814, 1817, 1820, 1822, 1825, 1828, 1830, 1833, 1836, 1838, 1841, 1843, 1846, 1848, 1851, 1853, 1855, 1858, 1860, 1863, 1865, 1867, 1870, 1872, 1874, 1877, 1879, 1881, 1884, 1886, 1888, 1890, 1892, 1895, 1897, 1899, 1901, 1903, 1905, 1908, 1910, 1912, 1914, 1916, 1918, 1920, 1922, 1924, 1926, 1928, 1930, 1932, 1934, 1936, 1938, 1940, 1942, 1944, 1946, 1947, 1949, 1951, 1953, 1955, 1957, 1959, 1961, 1962, 1964, 1966, 1968, 1970, 1971, 1973, 1975, 1977, 1978, 1980, 1982, 1984, 1985, 1987, 1989, 1990, 1992, 1994, 1995, 1997, 1999, 2000, 2002, 2004, 2005, 2007, 2008, 2010, 2012, 2013, 2015, 2016, 2018, 2020, 2021, 2023, 2024, 2026, 2027, 2029, 2030, 2032, 2033, 2035, 2036, 2038, 2039, 2041, 2042, 2044, 2045, 2047, 2048, 2049, 2051, 2052, 2054, 2055, 2057, 2058, 2059, 2061, 2062, 2064, 2065, 2066, 2068, 2069, 2070, 2072, 2073, 2074, 2076, 2077, 2078, 2080, 2081, 2082, 2084, 2085, 2086, 2088, 2089, 2090, 2092, 2093, 2094, 2095, 2097, 2098, 2099, 2100, 2102, 2103, 2104, 2105, 2107, 2108, 2109, 2110, 2111, 2113, 2114, 2115, 2116, 2117, 2119, 2120, 2121, 2122, 2123, 2125, 2126, 2127, 2128, 2129, 2130, 2132, 2133, 2134, 2135, 2136, 2137, 2138, 2140, 2141, 2142, 2143, 2144, 2145, 2146, 2147, 2148, 2150, 2151, 2152, 2153, 2154, 2155, 2156, 2157, 2158, 2159, 2160, 2161, 2162, 2164, 2165, 2166, 2167, 2168, 2169, 2170, 2171, 2172, 2173, 2174, 2175, 2176, 2177, 2178, 2179, 2180, 2181, 2182, 2183, 2184, 2185, 2186, 2187, 2188, 2189, 2190, 2191, 2192, 2193, 2194, 2195, 2196, 2197, 2198, 2199, 2200, 2201, 2202, 2203, 2203, 2204, 2205, 2206, 2207, 2208, 2209, 2210, 2211, 2212, 2213, 2214, 2215, 2216, 2217, 2217, 2218, 2219, 2220, 2221, 2222, 2223, 2224, 2225, 2226, 2226, 2227, 2228, 2229, 2230, 2231, 2232, 2233, 2233, 2234, 2235, 2236, 2237, 2238, 2239, 2240, 2240, 2241, 2242, 2243, 2244, 2245, 2246, 2246, 2247, 2248, 2249, 2250, 2251, 2251, 2252, 2253, 2254, 2255, 2256, 2256, 2257, 2258, 2259, 2260, 2260, 2261, 2262, 2263, 2264, 2264, 2265, 2266, 2267, 2268, 2268, 2269, 2270, 2271, 2272, 2272, 2273, 2274, 2275, 2276, 2276, 2277, 2278, 2279, 2279, 2280, 2281, 2282, 2282, 2283, 2284, 2285, 2286, 2286, 2287, 2288, 2289, 2289, 2290, 2291, 2292, 2292, 2293, 2294, 2295, 2295, 2296, 2297, 2297, 2298, 2299, 2300, 2300, 2301, 2302, 2303, 2303, 2304, }; // // 【ISP LV 计算】曝光最小 1/512 秒 // 输入 : X 曝光1/X 秒 (X 512) // 输出 : LV_Q8 // uint16_t calc_lv_final(uint16_t X, uint16_t A_Q8, uint16_t D_Q8, uint16_t I_Q8) { int32_t lv_result; uint16_t logX, logA, logD, logI; // 关键修正曝光 X 最小 512 if (X MIN_X) X MIN_X; // 强制最小 1/512s if (X MAX_INPUT) X MAX_INPUT; // 增益边界不变 if (A_Q8 MAX_GAIN) A_Q8 MAX_GAIN; if (D_Q8 MAX_GAIN) D_Q8 MAX_GAIN; if (I_Q8 MAX_GAIN) I_Q8 MAX_GAIN; // 查表 logX log2_q8_lut[X]; logA log2_x256_fast(A_Q8); logD log2_x256_fast(D_Q8); logI log2_x256_fast(I_Q8); // 公式不变 lv_result (int32_t)logX - logA - logD - logI LV_OFFSET; // 钳位 if (lv_result 256) lv_result 256; if (lv_result 512 * Q8) lv_result (512 * Q8); return (uint16_t)lv_result; }实际结果对比以下为误差较大的数据对比。估算值和excel计算值最大相差71。3.2 迭代版本2由迭代版本1结果可知log2_x256_fast(uint16_t x)计算精度相对还是较大因此使用三项多项式拟合定点计算提高计算精度。具体实现实例代码为//使用三阶多项式拟合log2函数 // 固定配置 #define Q8 256 // Q8 定点格式 #define LV_OFFSET (32 * Q8) // 固定偏移 32 #define MAX_INPUT 512 // X/A/D/I 最大值 #define MIN_X 4 // 曝光 X 最小值 #define MAX_GAIN (128*Q8) uint16_t log2_x256_fast(uint16_t x) { // 处理 f2.0 越界问题 if (x 32768) { return 3840; } uint8_t k; //if (x 32768) k 15; if (x 16384) k 14; else if (x 8192) k 13; else if (x 4096) k 12; else if (x 2048) k 11; else if (x 1024) k 10; else k 9; // 归一化到 [256, 512] Q8 uint16_t f_q8 (k 15) ? 512 : (x (k - 8)); int32_t d f_q8 - 256; int32_t d2 (int16_t)(((int32_t)d * d) 8); int32_t d3 (d2*d) 8; // 三阶多项式高精度近似 int32_t logf_q8 ((int32_t)d * 369 8) - ((int32_t)d2 * 185 8) (d3 * 85 8); // 最终 Q8 结果 return (int32_t)((k 8) logf_q8); } // // log2(x) Q8 查表 (0~512) // const uint16_t log2_q8_lut[MAX_INPUT 1] { 0, 0, 256, 406, 512, 594, 662, 719, 768, 812, 850, 886, 918, 947, 975, 1000, 1024, 1046, 1068, 1087, 1106, 1124, 1142, 1158, 1174, 1189, 1203, 1217, 1231, 1244, 1256, 1268, 1280, 1291, 1302, 1313, 1324, 1334, 1343, 1353, 1362, 1372, 1380, 1389, 1398, 1406, 1414, 1422, 1430, 1437, 1445, 1452, 1459, 1466, 1473, 1480, 1487, 1493, 1500, 1506, 1512, 1518, 1524, 1530, 1536, 1542, 1547, 1553, 1558, 1564, 1569, 1574, 1580, 1585, 1590, 1595, 1599, 1604, 1609, 1614, 1618, 1623, 1628, 1632, 1636, 1641, 1645, 1649, 1654, 1658, 1662, 1666, 1670, 1674, 1678, 1682, 1686, 1690, 1693, 1697, 1701, 1705, 1708, 1712, 1715, 1719, 1722, 1726, 1729, 1733, 1736, 1739, 1743, 1746, 1749, 1752, 1756, 1759, 1762, 1765, 1768, 1771, 1774, 1777, 1780, 1783, 1786, 1789, 1792, 1795, 1798, 1801, 1803, 1806, 1809, 1812, 1814, 1817, 1820, 1822, 1825, 1828, 1830, 1833, 1836, 1838, 1841, 1843, 1846, 1848, 1851, 1853, 1855, 1858, 1860, 1863, 1865, 1867, 1870, 1872, 1874, 1877, 1879, 1881, 1884, 1886, 1888, 1890, 1892, 1895, 1897, 1899, 1901, 1903, 1905, 1908, 1910, 1912, 1914, 1916, 1918, 1920, 1922, 1924, 1926, 1928, 1930, 1932, 1934, 1936, 1938, 1940, 1942, 1944, 1946, 1947, 1949, 1951, 1953, 1955, 1957, 1959, 1961, 1962, 1964, 1966, 1968, 1970, 1971, 1973, 1975, 1977, 1978, 1980, 1982, 1984, 1985, 1987, 1989, 1990, 1992, 1994, 1995, 1997, 1999, 2000, 2002, 2004, 2005, 2007, 2008, 2010, 2012, 2013, 2015, 2016, 2018, 2020, 2021, 2023, 2024, 2026, 2027, 2029, 2030, 2032, 2033, 2035, 2036, 2038, 2039, 2041, 2042, 2044, 2045, 2047, 2048, 2049, 2051, 2052, 2054, 2055, 2057, 2058, 2059, 2061, 2062, 2064, 2065, 2066, 2068, 2069, 2070, 2072, 2073, 2074, 2076, 2077, 2078, 2080, 2081, 2082, 2084, 2085, 2086, 2088, 2089, 2090, 2092, 2093, 2094, 2095, 2097, 2098, 2099, 2100, 2102, 2103, 2104, 2105, 2107, 2108, 2109, 2110, 2111, 2113, 2114, 2115, 2116, 2117, 2119, 2120, 2121, 2122, 2123, 2125, 2126, 2127, 2128, 2129, 2130, 2132, 2133, 2134, 2135, 2136, 2137, 2138, 2140, 2141, 2142, 2143, 2144, 2145, 2146, 2147, 2148, 2150, 2151, 2152, 2153, 2154, 2155, 2156, 2157, 2158, 2159, 2160, 2161, 2162, 2164, 2165, 2166, 2167, 2168, 2169, 2170, 2171, 2172, 2173, 2174, 2175, 2176, 2177, 2178, 2179, 2180, 2181, 2182, 2183, 2184, 2185, 2186, 2187, 2188, 2189, 2190, 2191, 2192, 2193, 2194, 2195, 2196, 2197, 2198, 2199, 2200, 2201, 2202, 2203, 2203, 2204, 2205, 2206, 2207, 2208, 2209, 2210, 2211, 2212, 2213, 2214, 2215, 2216, 2217, 2217, 2218, 2219, 2220, 2221, 2222, 2223, 2224, 2225, 2226, 2226, 2227, 2228, 2229, 2230, 2231, 2232, 2233, 2233, 2234, 2235, 2236, 2237, 2238, 2239, 2240, 2240, 2241, 2242, 2243, 2244, 2245, 2246, 2246, 2247, 2248, 2249, 2250, 2251, 2251, 2252, 2253, 2254, 2255, 2256, 2256, 2257, 2258, 2259, 2260, 2260, 2261, 2262, 2263, 2264, 2264, 2265, 2266, 2267, 2268, 2268, 2269, 2270, 2271, 2272, 2272, 2273, 2274, 2275, 2276, 2276, 2277, 2278, 2279, 2279, 2280, 2281, 2282, 2282, 2283, 2284, 2285, 2286, 2286, 2287, 2288, 2289, 2289, 2290, 2291, 2292, 2292, 2293, 2294, 2295, 2295, 2296, 2297, 2297, 2298, 2299, 2300, 2300, 2301, 2302, 2303, 2303, 2304, }; // // 【ISP LV 计算】曝光最小 1/512 秒 // 输入 : X 曝光1/X 秒 (X 512) // 输出 : LV_Q8 // uint16_t calc_lv_final(uint16_t X, uint16_t A_Q8, uint16_t D_Q8, uint16_t I_Q8) { int32_t lv_result; uint16_t logX, logA, logD, logI; // 关键修正曝光 X 最小 512 if (X MIN_X) X MIN_X; // 强制最小 1/512s if (X MAX_INPUT) X MAX_INPUT; // 增益边界不变 if (A_Q8 MAX_GAIN) A_Q8 MAX_GAIN; if (D_Q8 MAX_GAIN) D_Q8 MAX_GAIN; if (I_Q8 MAX_GAIN) I_Q8 MAX_GAIN; // 查表 logX log2_q8_lut[X]; if (A_Q8 MAX_INPUT) logA log2_q8_lut[A_Q8]; else logA log2_x256_fast(A_Q8); if (D_Q8 MAX_INPUT) logD log2_q8_lut[D_Q8]; else logD log2_x256_fast(D_Q8); if (D_Q8 MAX_INPUT) logI log2_q8_lut[I_Q8]; else logI log2_x256_fast(I_Q8); // 公式不变 lv_result (int32_t)logX - logA - logD - logI LV_OFFSET; // 钳位 if (lv_result 256) lv_result 256; if (lv_result 512 * Q8) lv_result (512 * Q8); return (uint16_t)lv_result; }实际结果对比以下为误差较大的数据对比。估算值和excel计算值最大相差12精度提高不少。3.3 迭代版本3既然使用三次多项式拟合定点能提高计算精度那么对于512以下的log2的Q8值计算是否也可以使用三次多项式拟合呢我们验证如下代码也可以达到不错的精度效果。具体实现实例代码为// 使用三阶多项式拟合log2函数 no lut // 固定配置 #define Q8 256 // Q8 定点格式 #define LV_OFFSET (32 * Q8) // 固定偏移 32 #define MAX_INPUT 512 // X/A/D/I 最大值 #define MIN_X 4 // 曝光 X #define MAX_GAIN (128*Q8) uint16_t log2_x256_fast(uint16_t x) { // 处理 f2.0 越界问题 if (x 32768) { return 3840; } uint8_t k; //if (x 32768) k 15; if (x 16384) k 14; else if (x 8192) k 13; else if (x 4096) k 12; else if (x 2048) k 11; else if (x 1024) k 10; else if (x 512) k 9; else if (x 256) k 8; else if (x 128) k 7; else if (x 64) k 6; else if (x 32) k 5; else if (x 16) k 4; else if (x 8) k 3; else if (x 4) k 2; else if (x 2) k 1; else k 0; // 归一化公式f_q8 x * 256 / 2^k // 全范围 1~32768 都正确永不出现负数移位 // uint32_t f_q8 ((uint32_t)x 8) k; // 归一化到 [256, 512] Q8 //uint16_t f_q8 (k 15) ? 512 : (x (k - 8)); int32_t d f_q8 - 256; int32_t d2 (int16_t)(((int32_t)d * d) 8); int32_t d3 (d2*d) 8; // 三阶多项式高精度近似 int32_t logf_q8 ((int32_t)d * 369 8) - ((int32_t)d2 * 185 8) (d3 * 85 8); // 最终 Q8 结果 return (int32_t)((k 8) logf_q8); } // // 【ISP LV 计算】曝光最小 1/512 秒 // 输入 : X 曝光1/X 秒 (X 512) // 输出 : LV_Q8 // uint16_t calc_lv_final(uint16_t X, uint16_t A_Q8, uint16_t D_Q8, uint16_t I_Q8) { int32_t lv_result; uint16_t logX, logA, logD, logI; // 关键修正曝光 X 最小 512 if (X MIN_X) X MIN_X; // 强制最小 1/512s if (X MAX_INPUT) X MAX_INPUT; // 增益边界不变 if (A_Q8 MAX_GAIN) A_Q8 MAX_GAIN; if (D_Q8 MAX_GAIN) D_Q8 MAX_GAIN; if (I_Q8 MAX_GAIN) I_Q8 MAX_GAIN; // 查表 logX log2_x256_fast(X); logA log2_x256_fast(A_Q8); logD log2_x256_fast(D_Q8); logI log2_x256_fast(I_Q8); // 公式不变 lv_result (int32_t)logX - logA - logD - logI LV_OFFSET; // 钳位 if (lv_result 256) lv_result 256; if (lv_result 512 * Q8) lv_result (512 * Q8); return (uint16_t)lv_result; }实际结果对比以下为误差较大的数据对比。估算值和excel计算值最大相差12。和方法2基本一致。但是统一了计算方式省去了查找表四、数据线性插值类似如下截图中相应权重的设置后我们即可在驱动块内部非常方便的根据LV的计算结果以及LV节点线性插值得到不同LV下的权重值。