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"""
2D visualization primitives based on Matplotlib.
1) Plot images with `plot_images`.
2) Call `plot_keypoints` or `plot_matches` any number of times.
3) Optionally: save a .png or .pdf plot (nice in papers!) with `save_plot`.
"""
import matplotlib
import matplotlib.pyplot as plt
import matplotlib.patheffects as path_effects
import numpy as np
def cm_RdGn(x):
"""Custom colormap: red (0) -> yellow (0.5) -> green (1)."""
x = np.clip(x, 0, 1)[..., None] * 2
c = x * np.array([[0, 1.0, 0]]) + (2 - x) * np.array([[1.0, 0, 0]])
return np.clip(c, 0, 1)
def plot_images(
imgs, titles=None, cmaps="gray", dpi=100, pad=0.5, adaptive=True
):
"""Plot a set of images horizontally.
Args:
imgs: a list of NumPy or PyTorch images, RGB (H, W, 3) or mono (H, W).
titles: a list of strings, as titles for each image.
cmaps: colormaps for monochrome images.
adaptive: whether the figure size should fit the image aspect ratios.
"""
n = len(imgs)
if not isinstance(cmaps, (list, tuple)):
cmaps = [cmaps] * n
if adaptive:
ratios = [i.shape[1] / i.shape[0] for i in imgs] # W / H
else:
ratios = [4 / 3] * n
figsize = [sum(ratios) * 4.5, 4.5]
fig, ax = plt.subplots(
1, n, figsize=figsize, dpi=dpi, gridspec_kw={"width_ratios": ratios}
)
if n == 1:
ax = [ax]
for i in range(n):
ax[i].imshow(imgs[i], cmap=plt.get_cmap(cmaps[i]))
ax[i].get_yaxis().set_ticks([])
ax[i].get_xaxis().set_ticks([])
ax[i].set_axis_off()
for spine in ax[i].spines.values(): # remove frame
spine.set_visible(False)
if titles:
ax[i].set_title(titles[i])
fig.tight_layout(pad=pad)
def plot_keypoints(kpts, colors="lime", ps=4):
"""Plot keypoints for existing images.
Args:
kpts: list of ndarrays of size (N, 2).
colors: string, or list of list of tuples (one for each keypoints).
ps: size of the keypoints as float.
"""
if not isinstance(colors, list):
colors = [colors] * len(kpts)
axes = plt.gcf().axes
try:
for a, k, c in zip(axes, kpts, colors):
a.scatter(k[:, 0], k[:, 1], c=c, s=ps, linewidths=0)
except IndexError as e:
pass
def plot_matches(kpts0, kpts1, color=None, lw=1.5, ps=4, indices=(0, 1), a=1.0):
"""Plot matches for a pair of existing images.
Args:
kpts0, kpts1: corresponding keypoints of size (N, 2).
color: color of each match, string or RGB tuple. Random if not given.
lw: width of the lines.
ps: size of the end points (no endpoint if ps=0)
indices: indices of the images to draw the matches on.
a: alpha opacity of the match lines.
"""
fig = plt.gcf()
ax = fig.axes
assert len(ax) > max(indices)
ax0, ax1 = ax[indices[0]], ax[indices[1]]
fig.canvas.draw()
assert len(kpts0) == len(kpts1)
if color is None:
color = matplotlib.cm.hsv(np.random.rand(len(kpts0))).tolist()
elif len(color) > 0 and not isinstance(color[0], (tuple, list)):
color = [color] * len(kpts0)
if lw > 0:
# transform the points into the figure coordinate system
transFigure = fig.transFigure.inverted()
fkpts0 = transFigure.transform(ax0.transData.transform(kpts0))
fkpts1 = transFigure.transform(ax1.transData.transform(kpts1))
fig.lines += [
matplotlib.lines.Line2D(
(fkpts0[i, 0], fkpts1[i, 0]),
(fkpts0[i, 1], fkpts1[i, 1]),
zorder=1,
transform=fig.transFigure,
c=color[i],
linewidth=lw,
alpha=a,
)
for i in range(len(kpts0))
]
# freeze the axes to prevent the transform to change
ax0.autoscale(enable=False)
ax1.autoscale(enable=False)
if ps > 0:
ax0.scatter(kpts0[:, 0], kpts0[:, 1], c=color, s=ps)
ax1.scatter(kpts1[:, 0], kpts1[:, 1], c=color, s=ps)
def add_text(
idx,
text,
pos=(0.01, 0.99),
fs=15,
color="w",
lcolor="k",
lwidth=2,
ha="left",
va="top",
):
ax = plt.gcf().axes[idx]
t = ax.text(
*pos,
text,
fontsize=fs,
ha=ha,
va=va,
color=color,
transform=ax.transAxes
)
if lcolor is not None:
t.set_path_effects(
[
path_effects.Stroke(linewidth=lwidth, foreground=lcolor),
path_effects.Normal(),
]
)
def save_plot(path, **kw):
"""Save the current figure without any white margin."""
plt.savefig(path, bbox_inches="tight", pad_inches=0, **kw)
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