python opencv: Use the slider to make the color palette

cv2.getTrackbarPos () function
parameter is the name of the slider,
the second argument is the name of the window slider is disposed,
the third parameter is the default position of the slider.
The fourth parameter is the maximum value of the slider,
the fifth function is a callback function that will be called every time the slider sliding callback function.
The callback function usually contain a default parameter is the position of the slider.
In this case, this function is not to do anything, we just need to pass it
slider Another important application is used as the conversion button.
OpenCV itself does not function with the button by default.
So we use the sliders instead.
In our program, we want to create a conversion button only when the button is installed for point to ON, slide the slider to be useful, otherwise all black windows account

import cv2
import numpy as np


def nothing(x):
    pass


# 创建一副黑色图像
img = np.zeros((300, 512, 3), np.uint8)
cv2.namedWindow('image')
cv2.createTrackbar('R', 'image', 0, 255, nothing)
cv2.createTrackbar('G', 'image', 0, 255, nothing)
cv2.createTrackbar('B', 'image', 0, 255, nothing)
switch = '0:OFF\n1:ON'
cv2.createTrackbar(switch, 'image', 0, 1, nothing)
while(1):
    cv2.imshow('image', img)
    k = cv2.waitKey(1) & 0xFF
    if k == 27:
        break
    r = cv2.getTrackbarPos('R', 'image')
    g = cv2.getTrackbarPos('G', 'image')
    b = cv2.getTrackbarPos('B', 'image')
    s = cv2.getTrackbarPos(switch, 'image')
    if s == 0:
        img[:] = 0
    else:
        img[:] = [b, g, r]
cv2.destroyAllWindows()

import cv2
import numpy as np


def nothing(x):
    pass


# 当鼠标按下时变为 True
drawing = False
# 如果 mode 为 true 绘制矩形。按下'm' 变成绘制曲线。
mode = True
ix, iy = -1, -1
# 创建回调函数


def draw_circle(event, x, y, flags, param):
    r = cv2.getTrackbarPos('R', 'image')
    g = cv2.getTrackbarPos('G', 'image')
    b = cv2.getTrackbarPos('B', 'image')
    color = (b, g, r)
    global ix, iy, drawing, mode
# 当按下左键是返回起始位置坐标
    if event == cv2.EVENT_LBUTTONDOWN:
        drawing = True
        ix, iy = x, y
# 当鼠标左键按下并移动是绘制图形。 event 可以查看移动， flag 查看是否按下
    elif event == cv2.EVENT_MOUSEMOVE and flags == cv2.EVENT_FLAG_LBUTTON:
        if drawing == True:
            if mode == True:
                cv2.rectangle(img, (ix, iy), (x, y), color, -1)
            else:
                # 绘制圆圈，小圆点连在一起就成了线， 3 代表了笔画的粗细
                cv2.circle(img, (x, y), 3, color, -1)
        # 下面注释掉的代码是起始点为圆心，起点到终点为半径的
        # r=int(np.sqrt((x-ix)**2+(y-iy)**2))
        # cv2.circle(img,(x,y),r,(0,0,255),-1)
        # 当鼠标松开停止绘画。
    elif event == cv2.EVENT_LBUTTONUP:
        drawing == False


        # if mode==True:
        # cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),-1)
        # else:
        # cv2.circle(img,(x,y),5,(0,0,255),-1)
img = np.zeros((512, 512, 3), np.uint8)
cv2.namedWindow('image')
cv2.createTrackbar('R', 'image', 0, 255, nothing)
cv2.createTrackbar('G', 'image', 0, 255, nothing)
cv2.createTrackbar('B', 'image', 0, 255, nothing)
cv2.setMouseCallback('image', draw_circle)
while(1):
    cv2.imshow('image', img)
    k = cv2.waitKey(1) & 0xFF
    if k == ord('m'):
        mode = not mode
    elif k == 27:
        break