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review.mlplatform.org / ml / ComputeLibrary / ebcebf1dee7f8314976b1e0cabd62b4cf893d765 / . / src / core / NEON / kernels / NEFastCornersKernel.cpp
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/*
* Copyright (c) 2016-2020 Arm Limited.
*
* SPDX-License-Identifier: MIT
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "src/core/NEON/kernels/NEFastCornersKernel.h"
#include "arm_compute/core/Coordinates.h"
#include "arm_compute/core/Error.h"
#include "arm_compute/core/Helpers.h"
#include "arm_compute/core/Validate.h"
#include "src/core/helpers/AutoConfiguration.h"
#include "src/core/helpers/WindowHelpers.h"
#include <algorithm>
#include <arm_neon.h>
#include <cstddef>
#include <limits>
using namespace arm_compute;
NEFastCornersKernel::NEFastCornersKernel()
: INEKernel(), _input(nullptr), _output(nullptr), _threshold(0), _non_max_suppression(false)
{
}
namespace
{
constexpr size_t PERMUTATIONS = 16;
constexpr size_t PERM_SIZE = 16;
inline uint8x8x2_t create_permutation_index(size_t k)
{
ARM_COMPUTE_ERROR_ON(k >= PERMUTATIONS);
static const std::array<std::array<uint8_t, PERMUTATIONS>, PERM_SIZE> permutations_table{ { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 255, 255, 255, 255, 255, 255, 255 },
{ 15, 0, 1, 2, 3, 4, 5, 6, 7, 255, 255, 255, 255, 255, 255, 255 },
{ 14, 15, 0, 1, 2, 3, 4, 5, 6, 255, 255, 255, 255, 255, 255, 255 },
{ 13, 14, 15, 0, 1, 2, 3, 4, 5, 255, 255, 255, 255, 255, 255, 255 },
{ 12, 13, 14, 15, 0, 1, 2, 3, 4, 255, 255, 255, 255, 255, 255, 255 },
{ 11, 12, 13, 14, 15, 0, 1, 2, 3, 255, 255, 255, 255, 255, 255, 255 },
{ 10, 11, 12, 13, 14, 15, 0, 1, 2, 255, 255, 255, 255, 255, 255, 255 },
{ 9, 10, 11, 12, 13, 14, 15, 0, 1, 255, 255, 255, 255, 255, 255, 255 },
{ 8, 9, 10, 11, 12, 13, 14, 15, 0, 255, 255, 255, 255, 255, 255, 255 },
{ 7, 8, 9, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255 },
{ 6, 7, 8, 9, 10, 11, 12, 13, 14, 255, 255, 255, 255, 255, 255, 255 },
{ 5, 6, 7, 8, 9, 10, 11, 12, 13, 255, 255, 255, 255, 255, 255, 255 },
{ 4, 5, 6, 7, 8, 9, 10, 11, 12, 255, 255, 255, 255, 255, 255, 255 },
{ 3, 4, 5, 6, 7, 8, 9, 10, 11, 255, 255, 255, 255, 255, 255, 255 },
{ 2, 3, 4, 5, 6, 7, 8, 9, 10, 255, 255, 255, 255, 255, 255, 255 },
{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255, 255, 255, 255, 255 }
} };
const uint8x8x2_t index =
{
{
vld1_u8(permutations_table[k].data()),
vld1_u8(permutations_table[k].data() + 8)
}
};
return index;
}
inline uint8x8x4_t create_circle_index_register()
{
/*
This function creates the index registers to retrieve the 16 texels in the Bresenham circle of radius 3 with center in P.
. . F 0 1 . . .
. E . . . 2 . .
D . . . . . 3 .
C . . P . . 4 .
B . . . . . 5 .
. A . . . 6 . .
. . 9 8 7 . . .
Where . is an irrelevant texel value
We want to retrieve all texels [0,F]
The 4 registers in r will then be used to get these texels out of two tables in the function get_circle_texels()
The first table holds the top 4 rows of texels
. . F 0 1 . . .
. E . . . 2 . .
D . . . . . 3 .
C . . P . . 4 .
The second table the bottom 3 rows of texels
B . . . . . 5 .
. A . . . 6 . .
. . 9 8 7 . . .
*/
static const std::array<uint8_t, 8> top_right =
{
/* The register r.val[0] will be used to retrieve these texels:
. . . 0 1 . . .
. . . . . 2 . .
. . . . . . 3 .
. . . . . . 4 .
*/
3 /* top table, first row, elem 4, value 0 in the diagram above */,
4 /* top table, first row, elem 5, value 1 in the diagram above */,
13 /* top table, second row, elem 6, value 2 in the diagram above */,
22 /* top table, third row, elem 7, value 3 in the diagram above*/,
30 /* top table, fourth row, elem 7, value 4 in the diagram above*/,
255,
255,
255
};
static const std::array<uint8_t, 8> bottom_right =
{
/* The register r.val[1] will be used to retrieve these texels:
. . . . . . 5 .
. . . . . 6 . .
. . . . 7 . . .
*/
255,
255,
255,
255,
255,
6 /* low table, first row, elem 7, value 5 in the diagram above*/,
13 /* low table, second row, elem 6, value 6 in the diagram above*/,
20 /* low table, third row, elem 5, value 7 in the diagram above*/
};
static const std::array<uint8_t, 8> top_left =
{
/* The register r.val[2] will be used to retrieve these texels:
. . F . . . . .
. E . . . . . .
D . . . . . . .
C . . . . . . .
*/
255,
255,
255,
255,
24 /* top table, fourth row, elem 1, value C in the diagram above */,
16 /* top table, third row, elem 1, value D in the diagram above*/,
9 /* top table, second row, elem 2, value E in the diagram above*/,
2 /* top table, first row, elem 3, value F in the diagram above*/
};
static const std::array<uint8_t, 8> bottom_left =
{
/* The register r.val[3] will be used to retrieve these texels:
B . . . . . . .
. A . . . . . .
. . 9 8 . . . .
*/
19 /* low table, third row, elem 4, value 8 in the diagram above */,
18 /* low table, third row, elem 3, value 9 in the diagram above */,
9 /* low table, second row, elem 2, value A in the diagram above */,
0 /* low table, first row, elem 1, value B in the diagram above */,
255,
255,
255,
255
};
const uint8x8x4_t reg =
{
{
vld1_u8(top_right.data()),
vld1_u8(bottom_right.data()),
vld1_u8(top_left.data()),
vld1_u8(bottom_left.data())
}
};
return reg;
}
inline uint8x16_t get_circle_texels(const uint8x8x4_t &index, const uint8x8x4_t &tbl_hi, const uint8x8x3_t &tbl_lo)
{
/*
This function loads the 16 texels in the Bresenham circle of radius 3 into the register 'texels'.
The parameter 'index' is an array of indices which was previously setup in setup_circle_index_register().
tbl_hi and tbl_lo are the two tables holding the texels in the window [(-3,-3),(+3,+3)] for a given texel P
*/
return vcombine_u8(vtbx3_u8(vtbl4_u8(tbl_hi, index.val[0]), tbl_lo, index.val[1]),
vtbx3_u8(vtbl4_u8(tbl_hi, index.val[2]), tbl_lo, index.val[3]));
}
inline uint8x16_t get_permutation_texels(const uint8x8x2_t &permutation_index, const uint8x8x2_t &tbl_circle)
{
/*
This function stores the 9 texels of a give permutation X in the neon register 'texels'
'tbl_circle' is a LUT with the texels 0 to F
. . F 0 1 . . .
. E . . . 2 . .
D . . . . . 3 .
C . . P . . 4 .
B . . . . . 5 .
. A . . . 6 . .
. . 9 8 7 . . .
'permutation_index' is one of the permutations below:
{ 0, 1, 2, 3, 4, 5, 6, 7, 8},
{ F, 0, 1, 2, 3, 4, 5, 6, 7},
{ E, F, 0, 1, 2, 3, 4, 5, 6},
{ D, E, F, 0, 1, 2, 3, 4, 5},
{ C, D, E, F, 0, 1, 2, 3, 4},
{ B, C, D, E, F, 0, 1, 2, 3},
{ A, B, C, D, E, F, 0, 1, 2},
{ 9, A, B, C, D, E, F, 0, 1},
{ 8, 9, A, B, C, D, E, F, 0},
{ 7, 8, 9, A, B, C, D, E, F},
{ 6, 7, 8, 9, A, B, C, D, E},
{ 5, 6, 7, 8, 9, A, B, C, D},
{ 4, 5, 6, 7, 8, 9, A, B, C},
{ 3, 4, 5, 6, 7, 8, 9, A, B},
{ 2, 3, 4, 5, 6, 7, 8, 9, A},
{ 1, 2, 3, 4, 5, 6, 7, 8, 9},
*/
static const uint8x8_t perm_right = vdup_n_u8(255); // init to 255 so that vtbx preserves the original values of the lanes
return vcombine_u8(vtbl2_u8(tbl_circle, permutation_index.val[0]),
vtbx2_u8(perm_right, tbl_circle, permutation_index.val[1]));
}
inline bool is_permutation_brighter(const uint8x16_t &permutation, const uint8x16_t &pg)
{
const uint8x16_t res_gt = vcgtq_u8(permutation, pg);
return vget_lane_u64(vreinterpret_u64_u8(vand_u8(vget_high_u8(res_gt), vget_low_u8(res_gt))), 0) == std::numeric_limits<uint64_t>::max();
}
inline bool is_permutation_darker(const uint8x16_t &permutation, const uint8x16_t &pl)
{
const uint8x16_t res_lt = vcltq_u8(permutation, pl);
const uint64x2_t u64res_lt = vreinterpretq_u64_u8(res_lt);
const uint64_t t3 = vgetq_lane_u64(u64res_lt, 0);
const uint64_t t4 = vgetq_lane_u64(u64res_lt, 1);
return std::numeric_limits<uint64_t>::max() == t3 && 255 == t4;
}
inline bool is_permutation_corner(const uint8x16_t &permutation, const uint8x16_t &pg, const uint8x16_t &pl)
{
return is_permutation_brighter(permutation, pg) || is_permutation_darker(permutation, pl);
}
inline bool point_is_fast_corner(uint8_t p, uint8_t threshold, const uint8x8x2_t &tbl_circle_texels, std::array<uint8x8x2_t, PERMUTATIONS> &perm_indices)
{
/*
This function determines whether the point 'p' is a corner.
*/
uint8x16_t pg = vqaddq_u8(vdupq_n_u8(p), vdupq_n_u8(threshold));
uint8x16_t pl = vqsubq_u8(vdupq_n_u8(p), vdupq_n_u8(threshold));
bool corner_detected = false;
for(size_t j = 0; !corner_detected && j < PERMUTATIONS; ++j)
{
const uint8x16_t pe_texels = get_permutation_texels(perm_indices[j], tbl_circle_texels);
corner_detected = is_permutation_corner(pe_texels, pg, pl);
}
return corner_detected;
}
inline uint8x8x2_t create_circle_tbl(const std::array<uint8_t *const __restrict, 7> &buffer, size_t in_offset, const uint8x8x4_t &circle_index_r)
{
/*
This function builds a LUT holding the 16 texels in the Brensenham circle radius 3.
circle_index_r is a vector of 4 registers to retrieve the texels from the two tables mentioned above.
*/
//Load the texels in the window [(x-3,y-3),(x+3,y+3)].
//The top 4 rows are loaded in tbl_hi and the low 3 rows in tbl_lo.
//These two tables are then used to retrieve the texels in the Bresenham circle of radius 3.
const uint8x8x4_t tbl_window_hi =
{
{
vld1_u8(buffer[0] + in_offset),
vld1_u8(buffer[1] + in_offset),
vld1_u8(buffer[2] + in_offset),
vld1_u8(buffer[3] + in_offset)
}
};
const uint8x8x3_t tbl_window_lo =
{
{
vld1_u8(buffer[4] + in_offset),
vld1_u8(buffer[5] + in_offset),
vld1_u8(buffer[6] + in_offset)
}
};
const uint8x16_t circle_texels = get_circle_texels(circle_index_r, tbl_window_hi, tbl_window_lo);
const uint8x8x2_t tbl_circle_texels =
{
{
vget_low_u8(circle_texels),
vget_high_u8(circle_texels)
}
};
return tbl_circle_texels;
}
inline uint8_t get_point_score(uint8_t p, uint8_t tolerance, const uint8x8x2_t &tbl_circle, std::array<uint8x8x2_t, PERMUTATIONS> &perm_indices)
{
uint8_t b = 255;
uint8_t a = tolerance;
while(b - a > 1)
{
const uint16_t ab = a + b;
const uint8_t c = ab >> 1;
if(point_is_fast_corner(p, c, tbl_circle, perm_indices))
{
a = c;
}
else
{
b = c;
}
}
return a;
}
} // namespace
BorderSize NEFastCornersKernel::border_size() const
{
return BorderSize(3);
}
void NEFastCornersKernel::configure(const IImage *input, IImage *output, uint8_t threshold, bool non_max_suppression, bool border_undefined)
{
ARM_COMPUTE_ERROR_ON_TENSOR_NOT_2D(input);
ARM_COMPUTE_ERROR_ON_TENSOR_NOT_2D(output);
ARM_COMPUTE_ERROR_ON_DATA_TYPE_CHANNEL_NOT_IN(input, 1, DataType::U8);
ARM_COMPUTE_ERROR_ON_DATA_TYPE_CHANNEL_NOT_IN(output, 1, DataType::U8);
ARM_COMPUTE_ERROR_ON_MSG(border_undefined == false, "Not implemented");
_input = input;
_output = output;
_threshold = threshold;
_non_max_suppression = non_max_suppression;
constexpr unsigned int num_elems_processed_per_iteration = 1;
constexpr unsigned int num_elems_read_per_iteration = 8;
constexpr unsigned int num_elems_written_per_iteration = 1;
constexpr unsigned int num_rows_read_per_iteration = 7;
// Configure kernel window
Window win = calculate_max_window(*input->info(), Steps(num_elems_processed_per_iteration), border_undefined, border_size());
AccessWindowHorizontal output_access(output->info(), 0, num_elems_written_per_iteration);
AccessWindowRectangle input_access(input->info(), -border_size().left, -border_size().top, num_elems_read_per_iteration, num_rows_read_per_iteration);
update_window_and_padding(win, input_access, output_access);
output_access.set_valid_region(win, input->info()->valid_region(), border_undefined, border_size());
INEKernel::configure(win);
}
void NEFastCornersKernel::run(const Window &window, const ThreadInfo &info)
{
ARM_COMPUTE_UNUSED(info);
ARM_COMPUTE_ERROR_ON_UNCONFIGURED_KERNEL(this);
ARM_COMPUTE_ERROR_ON_INVALID_SUBWINDOW(INEKernel::window(), window);
std::array<uint8x8x2_t, PERMUTATIONS> perm_index{ {} };
/*
We use a LUT loaded with 7 rows of uint8_t from the input image [-3,-3]...[+3,+3] to retrieve the texels in the Brensenham circle radius 3 and put them in one neon register uint8x16_t.
The three lines below setup the neon index registers to get these texels out from the table
*/
const uint8x8x4_t circle_index_r = create_circle_index_register();
/*
We put the 16 texels (circle) in a LUT to easily generate all the permutations. The for block below setups the indices for each permutation.
*/
for(size_t k = 0; k < PERMUTATIONS; ++k)
{
perm_index[k] = create_permutation_index(k);
}
Iterator in(_input, window);
Iterator out(_output, window);
const std::array<uint8_t *const __restrict, 7> in_row
{
_input->ptr_to_element(Coordinates(-3, -3)),
_input->ptr_to_element(Coordinates(-3, -2)),
_input->ptr_to_element(Coordinates(-3, -1)),
_input->ptr_to_element(Coordinates(-3, 0)),
_input->ptr_to_element(Coordinates(-3, 1)),
_input->ptr_to_element(Coordinates(-3, 2)),
_input->ptr_to_element(Coordinates(-3, 3))
};
auto is_rejected = [](uint8_t p, uint8_t q, uint8_t a, uint8_t b)
{
const bool p_is_in_ab = (a <= p) && (p <= b);
const bool q_is_in_ab = (a <= q) && (q <= b);
return p_is_in_ab && q_is_in_ab;
};
execute_window_loop(window, [&](const Coordinates &)
{
const size_t in_offset = in.offset();
const uint8_t p0 = *in.ptr();
const uint8_t b = std::min(p0 + _threshold, 255);
const uint8_t a = std::max(p0 - _threshold, 0);
uint8_t score = 0;
/*
Fast check to discard points which cannot be corners and avoid the expensive computation of the potential 16 permutations
pixels 1 and 9 are examined, if both I1 and I9 are within [Ip - t, Ip + t], then candidate p is not a corner.
*/
const uint8_t p1 = (in_offset + in_row[0])[3];
const uint8_t p9 = (in_offset + in_row[6])[3];
if(!is_rejected(p1, p9, a, b))
{
/* pixels 5 and 13 are further examined to check whether three of them are brighter than Ip + t or darker than Ip - t */
const uint8_t p5 = (in_offset + in_row[3])[6];
const uint8_t p13 = (in_offset + in_row[3])[0];
if(!is_rejected(p5, p13, a, b))
{
/* at this stage we use the full test with the 16 permutations to classify the point as corner or not */
const uint8x8x2_t tbl_circle_texel = create_circle_tbl(in_row, in_offset, circle_index_r);
if(point_is_fast_corner(p0, _threshold, tbl_circle_texel, perm_index))
{
if(_non_max_suppression)
{
score = get_point_score(p0, _threshold, tbl_circle_texel, perm_index);
}
else
{
score = 1;
}
}
}
}
*out.ptr() = score;
},
in, out);
}