def _cross_suppression(boxes, box_slice, iou_threshold, inner_idx):
batch_size = tf.shape(boxes)[0]
new_slice = tf.slice(boxes, [0, inner_idx * NMS_TILE_SIZE, 0],
[batch_size, NMS_TILE_SIZE, 4])
iou = box_ops.bbox_overlap(new_slice, box_slice)
ret_slice = tf.expand_dims(
tf.cast(tf.reduce_all(iou < iou_threshold, [1]), box_slice.dtype),
2) * box_slice
return boxes, ret_slice, iou_threshold, inner_idx + 1
def _suppression_loop_body(boxes, iou_threshold, output_size, idx):
"""Process boxes in the range [idx*NMS_TILE_SIZE, (idx+1)*NMS_TILE_SIZE).
Args:
boxes: a tensor with a shape of [batch_size, anchors, 4].
iou_threshold: a float representing the threshold for deciding whether boxes
overlap too much with respect to IOU.
output_size: an int32 tensor of size [batch_size]. Representing the number
of selected boxes for each batch.
idx: an integer scalar representing induction variable.
Returns:
boxes: updated boxes.
iou_threshold: pass down iou_threshold to the next iteration.
output_size: the updated output_size.
idx: the updated induction variable.
"""
num_tiles = tf.shape(boxes)[1] // NMS_TILE_SIZE
batch_size = tf.shape(boxes)[0]
# Iterates over tiles that can possibly suppress the current tile.
box_slice = tf.slice(boxes, [0, idx * NMS_TILE_SIZE, 0],
[batch_size, NMS_TILE_SIZE, 4])
_, box_slice, _, _ = tf.while_loop(
lambda _boxes, _box_slice, _threshold, inner_idx: inner_idx < idx,
_cross_suppression, [boxes, box_slice, iou_threshold,
tf.constant(0)])
# Iterates over the current tile to compute self-suppression.
iou = box_ops.bbox_overlap(box_slice, box_slice)
mask = tf.expand_dims(
tf.reshape(tf.range(NMS_TILE_SIZE), [1, -1]) > tf.reshape(
tf.range(NMS_TILE_SIZE), [-1, 1]), 0)
iou *= tf.cast(tf.logical_and(mask, iou >= iou_threshold), iou.dtype)
suppressed_iou, _, _ = tf.while_loop(
lambda _iou, loop_condition, _iou_sum: loop_condition,
_self_suppression,
[iou, tf.constant(True),
tf.reduce_sum(iou, [1, 2])])
suppressed_box = tf.reduce_sum(suppressed_iou, 1) > 0
box_slice *= tf.expand_dims(1.0 - tf.cast(suppressed_box, box_slice.dtype),
2)
# Uses box_slice to update the input boxes.
mask = tf.reshape(tf.cast(tf.equal(tf.range(num_tiles), idx), boxes.dtype),
[1, -1, 1, 1])
boxes = tf.tile(tf.expand_dims(
box_slice, [1]), [1, num_tiles, 1, 1]) * mask + tf.reshape(
boxes, [batch_size, num_tiles, NMS_TILE_SIZE, 4]) * (1 - mask)
boxes = tf.reshape(boxes, [batch_size, -1, 4])
# Updates output_size.
output_size += tf.reduce_sum(
tf.cast(tf.reduce_any(box_slice > 0, [2]), tf.int32), [1])
return boxes, iou_threshold, output_size, idx + 1
def random_crop_image_with_boxes_and_labels(img, boxes, labels, min_scale,
aspect_ratio_range,
min_overlap_params, max_retry):
"""Crops a random slice from the input image.
The function will correspondingly recompute the bounding boxes and filter out
outside boxes and their labels.
References:
[1] End-to-End Object Detection with Transformers
https://arxiv.org/abs/2005.12872
The preprocessing steps:
1. Sample a minimum IoU overlap.
2. For each trial, sample the new image width, height, and top-left corner.
3. Compute the IoUs of bounding boxes with the cropped image and retry if
the maximum IoU is below the sampled threshold.
4. Find boxes whose centers are in the cropped image.
5. Compute new bounding boxes in the cropped region and only select those
boxes' labels.
Args:
img: a 'Tensor' of shape [height, width, 3] representing the input image.
boxes: a 'Tensor' of shape [N, 4] representing the ground-truth bounding
boxes with (ymin, xmin, ymax, xmax).
labels: a 'Tensor' of shape [N,] representing the class labels of the boxes.
min_scale: a 'float' in [0.0, 1.0) indicating the lower bound of the random
scale variable.
aspect_ratio_range: a list of two 'float' that specifies the lower and upper
bound of the random aspect ratio.
min_overlap_params: a list of four 'float' representing the min value, max
value, step size, and offset for the minimum overlap sample.
max_retry: an 'int' representing the number of trials for cropping. If it is
exhausted, no cropping will be performed.
Returns:
img: a Tensor representing the random cropped image. Can be the
original image if max_retry is exhausted.
boxes: a Tensor representing the bounding boxes in the cropped image.
labels: a Tensor representing the new bounding boxes' labels.
"""
shape = tf.shape(img)
original_h = shape[0]
original_w = shape[1]
minval, maxval, step, offset = min_overlap_params
min_overlap = tf.math.floordiv(
tf.random.uniform([], minval=minval, maxval=maxval), step) * step - offset
min_overlap = tf.clip_by_value(min_overlap, 0.0, 1.1)
if min_overlap > 1.0:
return img, boxes, labels
aspect_ratio_low = aspect_ratio_range[0]
aspect_ratio_high = aspect_ratio_range[1]
for _ in tf.range(max_retry):
scale_h = tf.random.uniform([], min_scale, 1.0)
scale_w = tf.random.uniform([], min_scale, 1.0)
new_h = tf.cast(
scale_h * tf.cast(original_h, dtype=tf.float32), dtype=tf.int32)
new_w = tf.cast(
scale_w * tf.cast(original_w, dtype=tf.float32), dtype=tf.int32)
# Aspect ratio has to be in the prespecified range
aspect_ratio = new_h / new_w
if aspect_ratio_low > aspect_ratio or aspect_ratio > aspect_ratio_high:
continue
left = tf.random.uniform([], 0, original_w - new_w, dtype=tf.int32)
right = left + new_w
top = tf.random.uniform([], 0, original_h - new_h, dtype=tf.int32)
bottom = top + new_h
normalized_left = tf.cast(
left, dtype=tf.float32) / tf.cast(
original_w, dtype=tf.float32)
normalized_right = tf.cast(
right, dtype=tf.float32) / tf.cast(
original_w, dtype=tf.float32)
normalized_top = tf.cast(
top, dtype=tf.float32) / tf.cast(
original_h, dtype=tf.float32)
normalized_bottom = tf.cast(
bottom, dtype=tf.float32) / tf.cast(
original_h, dtype=tf.float32)
cropped_box = tf.expand_dims(
tf.stack([
normalized_top,
normalized_left,
normalized_bottom,
normalized_right,
]),
axis=0)
iou = box_ops.bbox_overlap(
tf.expand_dims(cropped_box, axis=0),
tf.expand_dims(boxes, axis=0)) # (1, 1, n_ground_truth)
iou = tf.squeeze(iou, axis=[0, 1])
# If not a single bounding box has a Jaccard overlap of greater than
# the minimum, try again
if tf.reduce_max(iou) < min_overlap:
continue
centroids = box_ops.yxyx_to_cycxhw(boxes)
mask = tf.math.logical_and(
tf.math.logical_and(centroids[:, 0] > normalized_top,
centroids[:, 0] < normalized_bottom),
tf.math.logical_and(centroids[:, 1] > normalized_left,
centroids[:, 1] < normalized_right))
# If not a single bounding box has its center in the crop, try again.
if tf.reduce_sum(tf.cast(mask, dtype=tf.int32)) > 0:
indices = tf.squeeze(tf.where(mask), axis=1)
filtered_boxes = tf.gather(boxes, indices)
boxes = tf.clip_by_value(
(filtered_boxes[..., :] * tf.cast(
tf.stack([original_h, original_w, original_h, original_w]),
dtype=tf.float32) -
tf.cast(tf.stack([top, left, top, left]), dtype=tf.float32)) /
tf.cast(tf.stack([new_h, new_w, new_h, new_w]), dtype=tf.float32),
0.0, 1.0)
img = tf.image.crop_to_bounding_box(img, top, left, bottom - top,
right - left)
labels = tf.gather(labels, indices)
break
return img, boxes, labels