python - 在 3D RGB numpy 数组中设置蒙版像素

Question

我想使用蒙版设置 3d numpy 数组(RGB 图像)中与某些条件匹配的所有像素。我有这样的东西:

def make_dot(img, color, radius):
    """Make a dot of given color in the center of img (rgb numpy array)"""
    (ydim,xdim,dummy) = img.shape
    # make an open grid of x,y
    y,x = np.ogrid[0:ydim, 0:xdim, ]
    y -= ydim/2                 # centered at the origin
    x -= xdim/2
    # now make a mask
    mask = x**2+y**2 <= radius**2 # start with 2d
    mask.shape = mask.shape + (1,) # make it 3d
    print img[mask].shape
    img[mask] = color

img = np.zeros((100, 200, 3))
make_dot(img, np.array((.1, .2, .3)), 25)

但这行给出 ValueError: array is not broadcastable to correct shape:

img[mask] = color

因为img[mask]的shape是(1961,);也就是说，它被展平为仅包含“有效”像素，这是有道理的；但是我怎样才能让它“通过掩码写入”，因为它只设置掩码为 1 的像素？请注意，我想一次将三个值写入每个像素(最后一个暗淡)。

Answer 1

你几乎是对的。

(ydim,xdim,dummy) = img.shape
# make an open grid of x,y
y,x = np.ogrid[0:ydim, 0:xdim, ]
y -= ydim/2                 # centered at the origin
x -= xdim/2
# now make a mask
mask = x**2+y**2 <= radius**2 # start with 2d
img[mask,:] = color

分配末尾的额外“,:”可让您一次分配整个 3 个 channel 的颜色。