COMPMID-344 Updated doxygen

Change-Id: I32f7b84daa560e460b77216add529c8fa8b327ae

1 files changed, 429 insertions, 0 deletions

diff --git a/src/core/CL/cl_kernels/canny.cl b/src/core/CL/cl_kernels/canny.cl
new file mode 100644
index 0000000000..ec6719213c
--- /dev/null
+++ b/src/core/CL/cl_kernels/canny.cl
@@ -0,0 +1,429 @@
+/*
+ * Copyright (c) 2017 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 "helpers.h"
+
+/** Calculate the magnitude and phase from horizontal and vertical result of sobel result.
+ *
+ * @note The calculation of gradient uses level 1 normalisation.
+ * @attention The input and output data types need to be passed at compile time using -DDATA_TYPE_IN and -DDATA_TYPE_OUT:
+ * e.g. -DDATA_TYPE_IN=uchar -DDATA_TYPE_OUT=short
+ *
+ * @param[in]  src1_ptr                            Pointer to the source image (Vertical result of Sobel). Supported data types: S16, S32
+ * @param[in]  src1_stride_x                       Stride of the source image in X dimension (in bytes)
+ * @param[in]  src1_step_x                         src1_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  src1_stride_y                       Stride of the source image in Y dimension (in bytes)
+ * @param[in]  src1_step_y                         src1_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  src1_offset_first_element_in_bytes  The offset of the first element in the source image
+ * @param[in]  src2_ptr                            Pointer to the source image (Vertical result of Sobel). Supported data types: S16, S32
+ * @param[in]  src2_stride_x                       Stride of the source image in X dimension (in bytes)
+ * @param[in]  src2_step_x                         src2_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  src2_stride_y                       Stride of the source image in Y dimension (in bytes)
+ * @param[in]  src2_step_y                         src2_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  src2_offset_first_element_in_bytes  The offset of the first element in the source image
+ * @param[out] grad_ptr                            Pointer to the gradient output. Supported data types: U16, U32
+ * @param[in]  grad_stride_x                       Stride of the source image in X dimension (in bytes)
+ * @param[in]  grad_step_x                         grad_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  grad_stride_y                       Stride of the source image in Y dimension (in bytes)
+ * @param[in]  grad_step_y                         grad_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  grad_offset_first_element_in_bytes  The offset of the first element of the output
+ * @param[out] angle_ptr                           Pointer to the angle output. Supported data types: U8
+ * @param[in]  angle_stride_x                      Stride of the source image in X dimension (in bytes)
+ * @param[in]  angle_step_x                        angle_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  angle_stride_y                      Stride of the source image in Y dimension (in bytes)
+ * @param[in]  angle_step_y                        angle_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  angle_offset_first_element_in_bytes The offset of the first element of the output
+ */
+__kernel void combine_gradients_L1(
+    IMAGE_DECLARATION(src1),
+    IMAGE_DECLARATION(src2),
+    IMAGE_DECLARATION(grad),
+    IMAGE_DECLARATION(angle))
+{
+    // Construct images
+    Image src1  = CONVERT_TO_IMAGE_STRUCT(src1);
+    Image src2  = CONVERT_TO_IMAGE_STRUCT(src2);
+    Image grad  = CONVERT_TO_IMAGE_STRUCT(grad);
+    Image angle = CONVERT_TO_IMAGE_STRUCT(angle);
+
+    // Load sobel horizontal and vertical values
+    VEC_DATA_TYPE(DATA_TYPE_IN, 4)
+    h = vload4(0, (__global DATA_TYPE_IN *)src1.ptr);
+    VEC_DATA_TYPE(DATA_TYPE_IN, 4)
+    v = vload4(0, (__global DATA_TYPE_IN *)src2.ptr);
+
+    /* Calculate the gradient, using level 1 normalisation method */
+    VEC_DATA_TYPE(DATA_TYPE_OUT, 4)
+    m = CONVERT_SAT((abs(h) + abs(v)), VEC_DATA_TYPE(DATA_TYPE_OUT, 4));
+
+    /* Calculate the angle */
+    float4 p = atan2pi(convert_float4(v), convert_float4(h));
+
+    /* Remap angle to range [0, 256) */
+    p = select(p, p + 2, p < 0.0f) * 128.0f;
+
+    /* Store results */
+    vstore4(m, 0, (__global DATA_TYPE_OUT *)grad.ptr);
+    vstore4(convert_uchar4_sat_rte(p), 0, angle.ptr);
+}
+
+/** Calculate the gradient and angle from horizontal and vertical result of sobel result.
+ *
+ * @note The calculation of gradient uses level 2 normalisation
+ * @attention The input and output data types need to be passed at compile time using -DDATA_TYPE_IN and -DDATA_TYPE_OUT:
+ * e.g. -DDATA_TYPE_IN=uchar -DDATA_TYPE_OUT=short
+ *
+ * @param[in]  src1_ptr                            Pointer to the source image (Vertical result of Sobel). Supported data types: S16, S32
+ * @param[in]  src1_stride_x                       Stride of the source image in X dimension (in bytes)
+ * @param[in]  src1_step_x                         src1_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  src1_stride_y                       Stride of the source image in Y dimension (in bytes)
+ * @param[in]  src1_step_y                         src1_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  src1_offset_first_element_in_bytes  The offset of the first element in the source image
+ * @param[in]  src2_ptr                            Pointer to the source image (Vertical result of Sobel). Supported data types: S16, S32
+ * @param[in]  src2_stride_x                       Stride of the source image in X dimension (in bytes)
+ * @param[in]  src2_step_x                         src2_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  src2_stride_y                       Stride of the source image in Y dimension (in bytes)
+ * @param[in]  src2_step_y                         src2_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  src2_offset_first_element_in_bytes  The offset of the first element in the source image
+ * @param[out] grad_ptr                            Pointer to the gradient output. Supported data types: U16, U32
+ * @param[in]  grad_stride_x                       Stride of the source image in X dimension (in bytes)
+ * @param[in]  grad_step_x                         grad_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  grad_stride_y                       Stride of the source image in Y dimension (in bytes)
+ * @param[in]  grad_step_y                         grad_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  grad_offset_first_element_in_bytes  The offset of the first element of the output
+ * @param[out] angle_ptr                           Pointer to the angle output. Supported data types: U8
+ * @param[in]  angle_stride_x                      Stride of the source image in X dimension (in bytes)
+ * @param[in]  angle_step_x                        angle_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  angle_stride_y                      Stride of the source image in Y dimension (in bytes)
+ * @param[in]  angle_step_y                        angle_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  angle_offset_first_element_in_bytes The offset of the first element of the output
+ */
+__kernel void combine_gradients_L2(
+    IMAGE_DECLARATION(src1),
+    IMAGE_DECLARATION(src2),
+    IMAGE_DECLARATION(grad),
+    IMAGE_DECLARATION(angle))
+{
+    // Construct images
+    Image src1  = CONVERT_TO_IMAGE_STRUCT(src1);
+    Image src2  = CONVERT_TO_IMAGE_STRUCT(src2);
+    Image grad  = CONVERT_TO_IMAGE_STRUCT(grad);
+    Image angle = CONVERT_TO_IMAGE_STRUCT(angle);
+
+    // Load sobel horizontal and vertical values
+    float4 h = convert_float4(vload4(0, (__global DATA_TYPE_IN *)src1.ptr));
+    float4 v = convert_float4(vload4(0, (__global DATA_TYPE_IN *)src2.ptr));
+
+    /* Calculate the gradient, using level 2 normalisation method */
+    float4 m = sqrt(h * h + v * v);
+
+    /* Calculate the angle */
+    float4 p = atan2pi(v, h);
+
+    /* Remap angle to range [0, 256) */
+    p = select(p, p + 2, p < 0.0f) * 128.0f;
+
+    /* Store results */
+    vstore4(CONVERT_SAT_ROUND(m, VEC_DATA_TYPE(DATA_TYPE_OUT, 4), rte), 0, (__global DATA_TYPE_OUT *)grad.ptr);
+    vstore4(convert_uchar4_sat_rte(p), 0, angle.ptr);
+}
+
+/** Array that holds the relative coordinates offset for the neighbouring pixels.
+ */
+__constant short4 neighbours_coords[] =
+{
+    { -1, 0, 1, 0 },  // 0
+    { -1, 1, 1, -1 }, // 45
+    { 0, 1, 0, -1 },  // 90
+    { 1, 1, -1, -1 }, // 135
+    { 1, 0, -1, 0 },  // 180
+    { 1, -1, -1, 1 }, // 225
+    { 0, 1, 0, -1 },  // 270
+    { -1, -1, 1, 1 }, // 315
+    { -1, 0, 1, 0 },  // 360
+};
+
+/** Perform non maximum suppression.
+ *
+ * @attention The input and output data types need to be passed at compile time using -DDATA_TYPE_IN and -DDATA_TYPE_OUT:
+ * e.g. -DDATA_TYPE_IN=uchar -DDATA_TYPE_OUT=short
+ *
+ * @param[in]  grad_ptr                              Pointer to the gradient output. Supported data types: S16, S32
+ * @param[in]  grad_stride_x                         Stride of the source image in X dimension (in bytes)
+ * @param[in]  grad_step_x                           grad_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  grad_stride_y                         Stride of the source image in Y dimension (in bytes)
+ * @param[in]  grad_step_y                           grad_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  grad_offset_first_element_in_bytes    The offset of the first element of the output
+ * @param[in]  angle_ptr                             Pointer to the angle output. Supported data types: U8
+ * @param[in]  angle_stride_x                        Stride of the source image in X dimension (in bytes)
+ * @param[in]  angle_step_x                          angle_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  angle_stride_y                        Stride of the source image in Y dimension (in bytes)
+ * @param[in]  angle_step_y                          angle_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  angle_offset_first_element_in_bytes   TThe offset of the first element of the output
+ * @param[out] non_max_ptr                           Pointer to the non maximum suppressed output. Supported data types: U16, U32
+ * @param[in]  non_max_stride_x                      Stride of the source image in X dimension (in bytes)
+ * @param[in]  non_max_step_x                        non_max_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  non_max_stride_y                      Stride of the source image in Y dimension (in bytes)
+ * @param[in]  non_max_step_y                        non_max_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  non_max_offset_first_element_in_bytes The offset of the first element of the output
+ * @param[in]  lower_thr                             The low threshold
+ */
+__kernel void suppress_non_maximum(
+    IMAGE_DECLARATION(grad),
+    IMAGE_DECLARATION(angle),
+    IMAGE_DECLARATION(non_max),
+    uint lower_thr)
+{
+    // Construct images
+    Image grad    = CONVERT_TO_IMAGE_STRUCT(grad);
+    Image angle   = CONVERT_TO_IMAGE_STRUCT(angle);
+    Image non_max = CONVERT_TO_IMAGE_STRUCT(non_max);
+
+    // Get gradient and angle
+    DATA_TYPE_IN gradient = *((__global DATA_TYPE_IN *)grad.ptr);
+    uchar an              = convert_ushort(*angle.ptr);
+
+    if(gradient <= lower_thr)
+    {
+        return;
+    }
+
+    // Divide the whole round into 8 directions
+    uchar         ang  = 127 - an;
+    DATA_TYPE_OUT q_an = (ang + 16) >> 5;
+
+    // Find the two pixels in the perpendicular direction
+    short2       x_p = neighbours_coords[q_an].s02;
+    short2       y_p = neighbours_coords[q_an].s13;
+    DATA_TYPE_IN g1  = *((global DATA_TYPE_IN *)offset(&grad, x_p.x, y_p.x));
+    DATA_TYPE_IN g2  = *((global DATA_TYPE_IN *)offset(&grad, x_p.y, y_p.y));
+
+    if((gradient > g1) && (gradient > g2))
+    {
+        *((global DATA_TYPE_OUT *)non_max.ptr) = gradient;
+    }
+}
+
+#define EDGE 255
+#define hysteresis_local_stack_L1 8  // The size of level 1 stack. This has to agree with the host side
+#define hysteresis_local_stack_L2 16 // The size of level 2 stack, adjust this can impact the match rate with VX implementation
+
+/** Check whether pixel is valid
+*
+* Skip the pixel if the early_test fails.
+* Otherwise, it tries to add the pixel coordinate to the stack, and proceed to popping the stack instead if the stack is full
+*
+* @param[in] early_test Boolean condition based on the minv check and visited buffer check
+* @param[in] x_pos      X-coordinate of pixel that is going to be recorded, has to be within the boundary
+* @param[in] y_pos      Y-coordinate of pixel that is going to be recorded, has to be within the boundary
+* @param[in] x_cur      X-coordinate of current central pixel
+* @param[in] y_cur      Y-coordinate of current central pixel
+*/
+#define check_pixel(early_test, x_pos, y_pos, x_cur, y_cur)                               \
+    {                                                                                     \
+        if(!early_test)                                                                   \
+        {                                                                                 \
+            /* Number of elements in the local stack 1, points to next available entry */ \
+            c = *((__global char *)offset(&l1_stack_counter, x_cur, y_cur));              \
+            \
+            if(c > (hysteresis_local_stack_L1 - 1)) /* Stack level 1 is full */           \
+                goto pop_stack;                                                           \
+            \
+            /* The pixel that has already been recorded is ignored */                     \
+            if(!atomic_or((__global uint *)offset(&recorded, x_pos, y_pos), 1))           \
+            {                                                                             \
+                l1_ptr[c] = (short2)(x_pos, y_pos);                                       \
+                *((__global char *)offset(&l1_stack_counter, x_cur, y_cur)) += 1;         \
+            }                                                                             \
+        }                                                                                 \
+    }
+
+/** Perform hysteresis.
+ *
+ * @attention The input data_type needs to be passed at compile time using -DDATA_TYPE_IN: e.g. -DDATA_TYPE_IN=short
+ *
+ * @param[in]  src_ptr                                        Pointer to the input image. Supported data types: U8
+ * @param[in]  src_stride_x                                   Stride of the source image in X dimension (in bytes)
+ * @param[in]  src_step_x                                     src_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  src_stride_y                                   Stride of the source image in Y dimension (in bytes)
+ * @param[in]  src_step_y                                     src_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  src_offset_first_element_in_bytes              The offset of the first element of the output
+ * @param[out] out_ptr                                        Pointer to the output image. Supported data types: U8
+ * @param[in]  out_stride_x                                   Stride of the source image in X dimension (in bytes)
+ * @param[in]  out_step_x                                     out_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  out_stride_y                                   Stride of the source image in Y dimension (in bytes)
+ * @param[in]  out_step_y                                     out_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  out_offset_first_element_in_bytes              The offset of the first element of the output
+ * @param[out] visited_ptr                                    Pointer to the visited buffer, where pixels are marked as visited. Supported data types: U32
+ * @param[in]  visited_stride_x                               Stride of the source image in X dimension (in bytes)
+ * @param[in]  visited_step_x                                 visited_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  visited_stride_y                               Stride of the source image in Y dimension (in bytes)
+ * @param[in]  visited_step_y                                 visited_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  visited_offset_first_element_in_bytes          The offset of the first element of the output
+ * @param[out] recorded_ptr                                   Pointer to the recorded buffer, where pixels are marked as recorded. Supported data types: U32
+ * @param[in]  recorded_stride_x                              Stride of the source image in X dimension (in bytes)
+ * @param[in]  recorded_step_x                                recorded_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  recorded_stride_y                              Stride of the source image in Y dimension (in bytes)
+ * @param[in]  recorded_step_y                                recorded_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  recorded_offset_first_element_in_bytes         The offset of the first element of the output
+ * @param[out] l1_stack_ptr                                   Pointer to the l1 stack of a pixel. Supported data types: S32
+ * @param[in]  l1_stack_stride_x                              Stride of the source image in X dimension (in bytes)
+ * @param[in]  l1_stack_step_x                                l1_stack_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  l1_stack_stride_y                              Stride of the source image in Y dimension (in bytes)
+ * @param[in]  l1_stack_step_y                                l1_stack_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  l1_stack_offset_first_element_in_bytes         The offset of the first element of the output
+ * @param[out] l1_stack_counter_ptr                           Pointer to the l1 stack counters of an image. Supported data types: U8
+ * @param[in]  l1_stack_counter_stride_x                      Stride of the source image in X dimension (in bytes)
+ * @param[in]  l1_stack_counter_step_x                        l1_stack_counter_stride_x * number of elements along X processed per workitem(in bytes)
+ * @param[in]  l1_stack_counter_stride_y                      Stride of the source image in Y dimension (in bytes)
+ * @param[in]  l1_stack_counter_step_y                        l1_stack_counter_stride_y * number of elements along Y processed per workitem(in bytes)
+ * @param[in]  l1_stack_counter_offset_first_element_in_bytes The offset of the first element of the output
+ * @param[in]  low_thr                                        The lower threshold
+ * @param[in]  up_thr                                         The upper threshold
+ * @param[in]  width                                          The width of the image.
+ * @param[in]  height                                         The height of the image
+ */
+kernel void hysteresis(
+    IMAGE_DECLARATION(src),
+    IMAGE_DECLARATION(out),
+    IMAGE_DECLARATION(visited),
+    IMAGE_DECLARATION(recorded),
+    IMAGE_DECLARATION(l1_stack),
+    IMAGE_DECLARATION(l1_stack_counter),
+    uint low_thr,
+    uint up_thr,
+    int  width,
+    int  height)
+{
+    // Create images
+    Image src              = CONVERT_TO_IMAGE_STRUCT_NO_STEP(src);
+    Image out              = CONVERT_TO_IMAGE_STRUCT_NO_STEP(out);
+    Image visited          = CONVERT_TO_IMAGE_STRUCT_NO_STEP(visited);
+    Image recorded         = CONVERT_TO_IMAGE_STRUCT_NO_STEP(recorded);
+    Image l1_stack         = CONVERT_TO_IMAGE_STRUCT_NO_STEP(l1_stack);
+    Image l1_stack_counter = CONVERT_TO_IMAGE_STRUCT_NO_STEP(l1_stack_counter);
+
+    // Index
+    int x = get_global_id(0);
+    int y = get_global_id(1);
+
+    // Load value
+    DATA_TYPE_IN val = *((__global DATA_TYPE_IN *)offset(&src, x, y));
+
+    // If less than upper threshold set to NO_EDGE and return
+    if(val <= up_thr)
+    {
+        *offset(&out, x, y) = 0;
+        return;
+    }
+
+    // Init local stack 2
+    short2 stack_L2[hysteresis_local_stack_L2] = { 0 };
+    int    L2_counter                          = 0;
+
+    // Perform recursive hysteresis
+    while(true)
+    {
+        // Get L1 stack pointer
+        __global short2 *l1_ptr = (__global short2 *)(l1_stack.ptr + y * l1_stack.stride_y + x * hysteresis_local_stack_L1 * l1_stack.stride_x);
+
+        // If the pixel has already been visited, proceed with the items in the stack instead
+        if(atomic_or((__global uint *)offset(&visited, x, y), 1) != 0)
+        {
+            goto pop_stack;
+        }
+
+        // Set strong edge
+        *offset(&out, x, y) = EDGE;
+
+        // If it is the top of stack l2, we don't need check the surrounding pixels
+        if(L2_counter > (hysteresis_local_stack_L2 - 1))
+        {
+            goto pop_stack2;
+        }
+
+        // Points to the start of the local stack;
+        char c;
+
+        VEC_DATA_TYPE(DATA_TYPE_IN, 4)
+        x_tmp;
+        uint4 v_tmp;
+
+        // Get direction pixel indices
+        int N = max(y - 1, 0), S = min(y + 1, height - 2), W = max(x - 1, 0), E = min(x + 1, width - 2);
+
+        // Check 8 pixels around for week edges where low_thr < val <= up_thr
+        x_tmp = vload4(0, (__global DATA_TYPE_IN *)offset(&src, W, N));
+        v_tmp = vload4(0, (__global uint *)offset(&visited, W, N));
+        check_pixel(((x_tmp.s0 <= low_thr) || v_tmp.s0 || (x_tmp.s0 > up_thr)), W, N, x, y); // NW
+        check_pixel(((x_tmp.s1 <= low_thr) || v_tmp.s1 || (x_tmp.s1 > up_thr)), x, N, x, y); // N
+        check_pixel(((x_tmp.s2 <= low_thr) || v_tmp.s2 || (x_tmp.s2 > up_thr)), E, N, x, y); // NE
+
+        x_tmp = vload4(0, (__global DATA_TYPE_IN *)offset(&src, W, y));
+        v_tmp = vload4(0, (__global uint *)offset(&visited, W, y));
+        check_pixel(((x_tmp.s0 <= low_thr) || v_tmp.s0 || (x_tmp.s0 > up_thr)), W, y, x, y); // W
+        check_pixel(((x_tmp.s2 <= low_thr) || v_tmp.s2 || (x_tmp.s2 > up_thr)), E, y, x, y); // E
+
+        x_tmp = vload4(0, (__global DATA_TYPE_IN *)offset(&src, W, S));
+        v_tmp = vload4(0, (__global uint *)offset(&visited, W, S));
+        check_pixel(((x_tmp.s0 <= low_thr) || v_tmp.s0 || (x_tmp.s0 > up_thr)), W, S, x, y); // SW
+        check_pixel(((x_tmp.s1 <= low_thr) || v_tmp.s1 || (x_tmp.s1 > up_thr)), x, S, x, y); // S
+        check_pixel(((x_tmp.s2 <= low_thr) || v_tmp.s2 || (x_tmp.s2 > up_thr)), E, S, x, y); // SE
+
+#undef check_pixel
+
+pop_stack:
+        c = *((__global char *)offset(&l1_stack_counter, x, y));
+
+        if(c >= 1)
+        {
+            *((__global char *)offset(&l1_stack_counter, x, y)) -= 1;
+            int2 l_c = convert_int2(l1_ptr[c - 1]);
+
+            // Push the current position into level 2 stack
+            stack_L2[L2_counter].x = x;
+            stack_L2[L2_counter].y = y;
+
+            x = l_c.x;
+            y = l_c.y;
+
+            L2_counter++;
+
+            continue;
+        }
+
+        if(L2_counter > 0)
+        {
+            goto pop_stack2;
+        }
+        else
+        {
+            return;
+        }
+
+pop_stack2:
+        L2_counter--;
+        x = stack_L2[L2_counter].x;
+        y = stack_L2[L2_counter].y;
+    };
+}