一、实现目标
在OpenCV中通过鼠标左键拖拽移动图片，通过鼠标滚轮前后旋转放大缩小图片。
二、实现背景
在前一篇博客在OpenCV中使用滚动条显示大图中发现自己画滚动条移动大图略显繁琐，且缩放图片存在一定不足，故尝试利用鼠标拖拽来实现图片移动，同时完善使用鼠标滚轮缩放图片的程序。
三、实现方法
利用OpenCV中的鼠标事件实现。当鼠标左键点击时保存初始坐标，按住鼠标左键并拖拽后记下拖拽坐标，二者相减得出相对移动坐标，最后以此计算窗口相对于大图的坐标(wx, wy)，并根据窗口宽高显示截取的图片。
四、运行环境
1. 在windows下已安装Python（必须的，我使用的是python3.7）;
2. 安装PyCharm（方便编程调试）
3. 安装opencv-python（在python下安装配置OpenCV）
五、运行代码
import cv2
def mouse(event, x, y, flags, param):
global flag, x1, y1, x2, y2, wx, wy, move_w, move_h, dst
global zoom, zoom_w, zoom_h, img_zoom, flag_har, flag_var
if event == cv2.EVENT_LBUTTONDOWN: # 左键点击
if flag == 0:
flag = 1
x1, y1, x2, y2 = x, y, wx, wy # 使鼠标移动距离都是相对于初始点击位置，而不是相对于上一位置
elif event == cv2.EVENT_MOUSEMOVE and (flags & cv2.EVENT_FLAG_LBUTTON): # 按住左键拖曳
if flag == 1:
move_w, move_h = x1 - x, y1 - y # 鼠标拖拽移动的宽高
if flag_har and flag_var: # 当窗口宽高大于图片宽高
wx = x2 + move_w # 窗口在大图的横坐标
if wx < 0: # 矫正位置
wx = 0
elif wx + win_w > zoom_w:
wx = zoom_w - win_w
wy = y2 + move_h # 窗口在大图的总坐标
if wy < 0:
wy = 0
elif wy + win_h > zoom_h:
wy = zoom_h - win_h
dst = img_zoom[wy:wy + win_h, wx:wx + win_w] # 截取窗口显示区域
elif flag_har and flag_var == 0: # 当窗口宽度大于图片宽度
wx = x2 + move_w
if wx < 0:
wx = 0
elif wx + win_w > zoom_w:
wx = zoom_w - win_w
dst = img_zoom[0:zoom_h, wx:wx + win_w]
elif flag_har == 0 and flag_var: # 当窗口高度大于图片高度
wy = y2 + move_h
if wy < 0:
wy = 0
elif wy + win_h > zoom_h:
wy = zoom_h - win_h
dst = img_zoom[wy:wy + win_h, 0:zoom_w]
elif event == cv2.EVENT_LBUTTONUP: # 左键释放
flag = 0
x1, y1, x2, y2 = 0, 0, 0, 0
elif event == cv2.EVENT_MOUSEWHEEL: # 滚轮
z = zoom
if flags > 0: # 滚轮上移
zoom += wheel_step
if zoom > 1 + wheel_step * 20: # 缩放倍数调整
zoom = 1 + wheel_step * 20
else: # 滚轮下移
zoom -= wheel_step
if zoom < wheel_step: # 缩放倍数调整
zoom = wheel_step
zoom = round(zoom, 2) # 取2位有效数字
zoom_w, zoom_h = int(img_original_w * zoom), int(img_original_h * zoom)
# print(wx, wy)
wx, wy = int((wx + x) * zoom / z - x), int((wy + y) * zoom / z - y) # 缩放后窗口在图片中的坐标
# print(z, zoom, x, y, wx, wy)
if wx < 0:
wx = 0
elif wx + win_w > zoom_w:
wx = zoom_w - win_w
if wy < 0:
wy = 0
elif wy + win_h > zoom_h:
wy = zoom_h - win_h
img_zoom = cv2.resize(img_original, (zoom_w, zoom_h), interpolation=cv2.INTER_AREA) # 图片缩放
if zoom_w <= win_w and zoom_h <= win_h: # 缩放后图片宽高小于窗口宽高
flag_har, flag_var = 0, 0
dst = img_zoom
cv2.resizeWindow('img', zoom_w, zoom_h)
elif zoom_w <= win_w and zoom_h > win_h: # 缩放后图片宽度小于窗口宽度
flag_har, flag_var = 0, 1
dst = img_zoom[wy:wy + win_h, 0:zoom_w]
cv2.resizeWindow('img', zoom_w, win_h)
elif zoom_w > win_w and zoom_h <= win_h: # 缩放后图片高度小于窗口高度
flag_har, flag_var = 1, 0
dst = img_zoom[0:zoom_h, wx:wx + win_w]
cv2.resizeWindow('img', win_w, zoom_h)
else: # 缩放后图片宽高大于于窗口宽高
flag_har, flag_var = 1, 1
dst = img_zoom[wy:wy + win_h, wx:wx + win_w]
cv2.resizeWindow('img', win_w, win_h)
cv2.imshow("img", dst)
cv2.waitKey(1)
win_h, win_w = 600, 800 # 窗口宽高
wx, wy = 0, 0 # 窗口相对于原图的坐标
wheel_step, zoom = 0.05, 1 # 缩放系数， 缩放值
img_original = cv2.imread("E:/VSCode/git/my_program/ImageMoveZoom/1.jpg") # 建议图片大于win_w*win_h(800*600)
img_original_h, img_original_w = img_original.shape[0:2] # 原图宽高
cv2.namedWindow('img', cv2.WINDOW_NORMAL)
cv2.moveWindow("img", 300, 100)
zoom_w, zoom_h = img_original_w, img_original_h # 缩放图宽高
img_zoom = img_original.copy() # 缩放图片
flag, flag_har, flag_var = 0, 0, 0 # 鼠标操作类型
move_w, move_h = 0, 0 # 鼠标移动坐标
x1, y1, x2, y2 = 0, 0, 0, 0 # 中间变量
cv2.resizeWindow("img", win_w, win_h)
dst = img_original[wy:wy + win_h, wx:wx + win_w]
cv2.setMouseCallback('img', mouse)
if img_original_w > win_w:
flag_har = 1
if img_original_h > win_h:
flag_var = 1
cv2.waitKey()
cv2.destroyAllWindows()
2020.06.02版本：缩减全局变量个数，将关联较少的功能（如矫正坐标，计算缩放倍数）单独定义成函数，精炼鼠标事件函数。
import cv2
# 全局变量
g_window_name = "img" # 窗口名
g_window_wh = [800, 600] # 窗口宽高
g_location_win = [0, 0] # 相对于大图，窗口在图片中的位置
location_win = [0, 0] # 鼠标左键点击时，暂存g_location_win
g_location_click, g_location_release = [0, 0], [0, 0] # 相对于窗口，鼠标左键点击和释放的位置
g_zoom, g_step = 1, 0.1 # 图片缩放比例和缩放系数
g_image_original = cv2.imread("E:/VSCode/git/my_program/ImageMoveZoom/1.jpg") # 原始图片，建议大于窗口宽高（800*600）
g_image_zoom = g_image_original.copy() # 缩放后的图片
g_image_show = g_image_original[g_location_win[1]:g_location_win[1] + g_window_wh[1], g_location_win[0]:g_location_win[0] + g_window_wh[0]] # 实际显示的图片
# 矫正窗口在图片中的位置
# img_wh:图片的宽高, win_wh:窗口的宽高, win_xy:窗口在图片的位置
def check_location(img_wh, win_wh, win_xy):
for i in range(2):
if win_xy[i] < 0:
win_xy[i] = 0
elif win_xy[i] + win_wh[i] > img_wh[i] and img_wh[i] > win_wh[i]:
win_xy[i] = img_wh[i] - win_wh[i]
elif win_xy[i] + win_wh[i] > img_wh[i] and img_wh[i] < win_wh[i]:
win_xy[i] = 0
# print(img_wh, win_wh, win_xy)
# 计算缩放倍数
# flag：鼠标滚轮上移或下移的标识, step：缩放系数，滚轮每步缩放0.1, zoom：缩放倍数
def count_zoom(flag, step, zoom):
if flag > 0: # 滚轮上移
zoom += step
if zoom > 1 + step * 20: # 最多只能放大到3倍
zoom = 1 + step * 20
else: # 滚轮下移
zoom -= step
if zoom < step: # 最多只能缩小到0.1倍
zoom = step
zoom = round(zoom, 2) # 取2位有效数字
return zoom
# OpenCV鼠标事件
def mouse(event, x, y, flags, param):
global g_location_click, g_location_release, g_image_show, g_image_zoom, g_location_win, location_win, g_zoom
if event == cv2.EVENT_LBUTTONDOWN: # 左键点击
g_location_click = [x, y] # 左键点击时，鼠标相对于窗口的坐标
location_win = [g_location_win[0], g_location_win[1]] # 窗口相对于图片的坐标，不能写成location_win = g_location_win
elif event == cv2.EVENT_MOUSEMOVE and (flags & cv2.EVENT_FLAG_LBUTTON): # 按住左键拖曳
g_location_release = [x, y] # 左键拖曳时，鼠标相对于窗口的坐标
h1, w1 = g_image_zoom.shape[0:2] # 缩放图片的宽高
w2, h2 = g_window_wh # 窗口的宽高
show_wh = [0, 0] # 实际显示图片的宽高
if w1 < w2 and h1 < h2: # 图片的宽高小于窗口宽高，无法移动
show_wh = [w1, h1]
g_location_win = [0, 0]
elif w1 >= w2 and h1 < h2: # 图片的宽度大于窗口的宽度，可左右移动
show_wh = [w2, h1]
g_location_win[0] = location_win[0] + g_location_click[0] - g_location_release[0]
elif w1 < w2 and h1 >= h2: # 图片的高度大于窗口的高度，可上下移动
show_wh = [w1, h2]
g_location_win[1] = location_win[1] + g_location_click[1] - g_location_release[1]
else: # 图片的宽高大于窗口宽高，可左右上下移动
show_wh = [w2, h2]
g_location_win[0] = location_win[0] + g_location_click[0] - g_location_release[0]
g_location_win[1] = location_win[1] + g_location_click[1] - g_location_release[1]
check_location([w1, h1], [w2, h2], g_location_win) # 矫正窗口在图片中的位置
g_image_show = g_image_zoom[g_location_win[1]:g_location_win[1] + show_wh[1], g_location_win[0]:g_location_win[0] + show_wh[0]] # 实际显示的图片
elif event == cv2.EVENT_MOUSEWHEEL: # 滚轮
z = g_zoom # 缩放前的缩放倍数，用于计算缩放后窗口在图片中的位置
g_zoom = count_zoom(flags, g_step, g_zoom) # 计算缩放倍数
w1, h1 = [int(g_image_original.shape[1] * g_zoom), int(g_image_original.shape[0] * g_zoom)] # 缩放图片的宽高
w2, h2 = g_window_wh # 窗口的宽高
g_image_zoom = cv2.resize(g_image_original, (w1, h1), interpolation=cv2.INTER_AREA) # 图片缩放
show_wh = [0, 0] # 实际显示图片的宽高
if w1 < w2 and h1 < h2: # 缩放后，图片宽高小于窗口宽高
show_wh = [w1, h1]
cv2.resizeWindow(g_window_name, w1, h1)
elif w1 >= w2 and h1 < h2: # 缩放后，图片高度小于窗口高度
show_wh = [w2, h1]
cv2.resizeWindow(g_window_name, w2, h1)
elif w1 < w2 and h1 >= h2: # 缩放后，图片宽度小于窗口宽度
show_wh = [w1, h2]
cv2.resizeWindow(g_window_name, w1, h2)
else: # 缩放后，图片宽高大于窗口宽高
show_wh = [w2, h2]
cv2.resizeWindow(g_window_name, w2, h2)
g_location_win = [int((g_location_win[0] + x) * g_zoom / z - x), int((g_location_win[1] + y) * g_zoom / z - y)] # 缩放后，窗口在图片的位置
check_location([w1, h1], [w2, h2], g_location_win) # 矫正窗口在图片中的位置
# print(g_location_win, show_wh)
g_image_show = g_image_zoom[g_location_win[1]:g_location_win[1] + show_wh[1], g_location_win[0]:g_location_win[0] + show_wh[0]] # 实际的显示图片
cv2.imshow(g_window_name, g_image_show)
# 主函数
if __name__ == "__main__":
# 设置窗口
cv2.namedWindow(g_window_name, cv2.WINDOW_NORMAL)
# 设置窗口大小，只有当图片大于窗口时才能移动图片
cv2.resizeWindow(g_window_name, g_window_wh[0], g_window_wh[1])
cv2.moveWindow(g_window_name, 700, 100) # 设置窗口在电脑屏幕中的位置
# 鼠标事件的回调函数
cv2.setMouseCallback(g_window_name, mouse)
cv2.waitKey() # 不可缺少，用于刷新图片，等待鼠标操作
cv2.destroyAllWindows()
六、运行结果
原图：
水平移动图片（鼠标左键点击并向左拖拽）：
垂直移动图片（鼠标左键点击，向上拖拽）：
鼠标滚轮后转缩小图片：
鼠标滚轮前转放大图片：
