| """ |
| Generate base anchors on index 0 |
| """ |
| |
| import numpy as np |
| |
| |
| def generate_anchors(base_size=16, ratios=[0.5, 1, 2], |
| scales=2 ** np.arange(3, 6)): |
| """ |
| Generate anchor (reference) windows by enumerating aspect ratios X |
| scales wrt a reference (0, 0, 15, 15) window. |
| """ |
| |
| base_anchor = np.array([1, 1, base_size, base_size]) - 1 |
| ratio_anchors = _ratio_enum(base_anchor, ratios) |
| anchors = np.vstack([_scale_enum(ratio_anchors[i, :], scales) |
| for i in xrange(ratio_anchors.shape[0])]) |
| return anchors |
| |
| |
| def _whctrs(anchor): |
| """ |
| Return width, height, x center, and y center for an anchor (window). |
| """ |
| |
| w = anchor[2] - anchor[0] + 1 |
| h = anchor[3] - anchor[1] + 1 |
| x_ctr = anchor[0] + 0.5 * (w - 1) |
| y_ctr = anchor[1] + 0.5 * (h - 1) |
| return w, h, x_ctr, y_ctr |
| |
| |
| def _mkanchors(ws, hs, x_ctr, y_ctr): |
| """ |
| Given a vector of widths (ws) and heights (hs) around a center |
| (x_ctr, y_ctr), output a set of anchors (windows). |
| """ |
| |
| ws = ws[:, np.newaxis] |
| hs = hs[:, np.newaxis] |
| anchors = np.hstack((x_ctr - 0.5 * (ws - 1), |
| y_ctr - 0.5 * (hs - 1), |
| x_ctr + 0.5 * (ws - 1), |
| y_ctr + 0.5 * (hs - 1))) |
| return anchors |
| |
| |
| def _ratio_enum(anchor, ratios): |
| """ |
| Enumerate a set of anchors for each aspect ratio wrt an anchor. |
| """ |
| |
| w, h, x_ctr, y_ctr = _whctrs(anchor) |
| size = w * h |
| size_ratios = size / ratios |
| ws = np.round(np.sqrt(size_ratios)) |
| hs = np.round(ws * ratios) |
| anchors = _mkanchors(ws, hs, x_ctr, y_ctr) |
| return anchors |
| |
| |
| def _scale_enum(anchor, scales): |
| """ |
| Enumerate a set of anchors for each scale wrt an anchor. |
| """ |
| |
| w, h, x_ctr, y_ctr = _whctrs(anchor) |
| ws = w * scales |
| hs = h * scales |
| anchors = _mkanchors(ws, hs, x_ctr, y_ctr) |
| return anchors |
