python - 如何使矩形透明？

Question

所以我正在使用opencv，我想做一种选择工具，但是问题是不能使矩形透明。这是代码:

import numpy as np
import cv2 as cv
drawing = False

def draw_rec(event,x,y,flags,param):
    global ix,iy,drawing
    if event == cv.EVENT_LBUTTONDOWN:
        drawing = True
        ix,iy = x,y
    elif event == cv.EVENT_LBUTTONUP:
        drawing = False
        cv.rectangle(img,(ix,iy),(x,y),(0,0,0),-1)
    elif event == cv.EVENT_MOUSEMOVE:
        if drawing == True:
            cv.rectangle(img, (ix, iy), (x, y), (0, 255, 0), 5)
img = cv.imread('baboon.jpg', -1)
cv.namedWindow('image')
cv.setMouseCallback('image',draw_rec)
while(1):
    cv.imshow('image',img)
    k = cv.waitKey(1) & 0xFF
    if k == 27:
        break
cv.destroyAllWindows()

Answer 1

代码中的第一个错误是:

elif event == cv.EVENT_LBUTTONUP:
        drawing = False
        cv.rectangle(img,(ix,iy),(x,y),(0,0,0),-1)

-1参数表示填充矩形。 source如果将-1更改为1:

从我的 Angular 来看，结果并不令人满意。多矩形显示是由 mouse_movement引起的。

elif event == cv.EVENT_MOUSEMOVE:
        if drawing == True:
            cv.rectangle(img, (ix, iy), (x, y), (0, 255, 0), 5)

每次鼠标移动时，都会绘制矩形。我认为最好在鼠标移动结束后进行绘制:

码:

import numpy as np
import cv2 as cv
drawing = False

def draw_rec(event,x,y,flags,param):
    global ix,iy,drawing
    if event == cv.EVENT_LBUTTONDOWN:
        drawing = True
        ix,iy = x,y
    elif event == cv.EVENT_LBUTTONUP:
        drawing = False
        cv.rectangle(img,(ix,iy),(x,y),(0,255,0),5)


img = cv.imread('27BR1.jpg', -1)
cv.namedWindow('image')
cv.setMouseCallback('image',draw_rec)
while(1):
    cv.imshow('image',img)
    k = cv.waitKey(1) & 0xFF
    if k == 27:
        break
cv.destroyAllWindows()