前面学习过寻找图像的边缘，需要在图像标记出来，这时就需要在图像上画一些图形，那么这里就来学习cv.line(), cv.circle() , cv.rectangle(), cv.ellipse()来怎么样绘制图形的，以及使用cv.putText()输出文本。下面来看一下cv.line()函数的定义：
img 绘制的图像
pt1 直线的起点
pt2 直线的终点
color 直线颜色
thickness 直线的粗细
lineType 直线的绘制方式
shift 坐标点的小数点位数
其它函数的参数大同小异，通过下面的例子来演示：
#python 3.7.4,opencv4.1
#蔡军生 https://blog.csdn.net/caimouse/article/details/51749579
#
import numpy as np
import cv2
from matplotlib import pyplot as plt
import freetype
#使用freetype显示中文类
class put_chinese_text(object):
def __init__(self, ttf):
self._face = freetype.Face(ttf)
def draw_text(self, image, pos, text, text_size, text_color):
'''
draw chinese(or not) text with ttf
:param image: image(numpy.ndarray) to draw text
:param pos: where to draw text
:param text: the context, for chinese should be unicode type
:param text_size: text size
:param text_color:text color
:return: image '''
self._face.set_char_size(text_size * 64)
metrics = self._face.size
ascender = metrics.ascender/64.0
ypos = int(ascender)
image = self.draw_string(image, pos[0], pos[1]+ypos, text, text_color)
return image
def draw_string(self, image, x_pos, y_pos, text, color):
''' draw string
:param x_pos: text x-postion on image
:param y_pos: text y-postion on image
:param text: text (unicode)
:param color: text color
:return: image
'''
prev_char = 0
pen = freetype.Vector()
pen.x = x_pos << 6 # div 64
pen.y = y_pos << 6
hscale = 1.0
matrix = freetype.Matrix(int(hscale)*0x10000, int(0.2*0x10000),\
int(0.0*0x10000), int(1.1*0x10000))
cur_pen = freetype.Vector()
pen_translate = freetype.Vector()
for cur_char in text:
self._face.set_transform(matrix, pen_translate)
self._face.load_char(cur_char)
kerning = self._face.get_kerning(prev_char, cur_char)
pen.x += kerning.x
slot = self._face.glyph
bitmap = slot.bitmap
cur_pen.x = pen.x
cur_pen.y = pen.y - slot.bitmap_top * 64
self.draw_ft_bitmap(image, bitmap, cur_pen, color)
pen.x += slot.advance.x
prev_char = cur_char
return image
def draw_ft_bitmap(self, img, bitmap, pen, color):
'''
draw each char
:param bitmap: bitmap
:param pen: pen
:param color: pen color e.g.(0,0,255) - red
:return: image
'''
x_pos = pen.x >> 6
y_pos = pen.y >> 6
cols = bitmap.width
rows = bitmap.rows
glyph_pixels = bitmap.buffer
for row in range(rows):
for col in range(cols):
if glyph_pixels[row*cols + col] != 0:
img[y_pos + row,x_pos + col] = color
# 创建一个黑色彩色图像
img = np.zeros((512,512,3), np.uint8)
# 画一条5像素宽的蓝色直线,注意颜色顺序是（B,G,R）
cv2.line(img,(0,0),(511,511),(255,0,0),5)
#画圆
cv2.circle(img,(447,63), 63, (0,0,255), -1)
#画椭圆
cv2.ellipse(img,(256,256),(100,50),0,0,180,255,-1)
#画多边形
pts = np.array([[10,5],[20,30],[70,20],[50,10]], np.int32)
pts = pts.reshape((-1,1,2))
cv2.polylines(img,[pts],True,(0,255,255))
#输出文字
font = cv2.FONT_HERSHEY_SIMPLEX
cv2.putText(img,'OpenCV',(10,500), font, 4,(255,255,255),2,cv2.LINE_AA)
#显示中文
color_ = (0,255,0) # (B,G,R) 中文显示颜色
pos = (30, 100) #显示位置
text_size = 24 #文字大小
lineTxt = '深圳先行示范区' #要显示文字
ft = put_chinese_text("C:/windows/fonts/simfang.ttf") #使用windows下的字体
image = ft.draw_text(img, pos, lineTxt, text_size, color_)
cv2.imshow('Out', image)
cv2.waitKey(0)
cv2.destroyAllWindows()
结果输出如下
在这个例子里，显示英文字符都是很简单的事情，因为OpenCV直接支持输出，如果要显示中文就不简单了，需要先安装freetype-py,并且要按freetype的方式生成bmp，再按字体的格式来显示像素。如果没有安装它，可以按下面命令进行安装：
pip install freetype-py
然后定义一个类来显示中文：
#使用freetype显示中文类
class put_chinese_text(object):
这里是构造函数，调用freetype.Face读取字体。
def __init__(self, ttf):
self._face = freetype.Face(ttf)
显示一行文字的函数
def draw_text(self, image, pos, text, text_size, text_color):
'''
draw chinese(or not) text with ttf
:param image: image(numpy.ndarray) to draw text
:param pos: where to draw text
:param text: the context, for chinese should be unicode type
:param text_size: text size
:param text_color:text color
:return: image '''
self._face.set_char_size(text_size * 64)
metrics = self._face.size
ascender = metrics.ascender/64.0
ypos = int(ascender)
image = self.draw_string(image, pos[0], pos[1]+ypos, text, text_color)
return image
根据计算出来的坐标位置显示字符串
def draw_string(self, image, x_pos, y_pos, text, color):
''' draw string
:param x_pos: text x-postion on image
:param y_pos: text y-postion on image
:param text: text (unicode)
:param color: text color
:return: image
'''
prev_char = 0
pen = freetype.Vector()
pen.x = x_pos << 6 # div 64
pen.y = y_pos << 6
hscale = 1.0
matrix = freetype.Matrix(int(hscale)*0x10000, int(0.2*0x10000),\
int(0.0*0x10000), int(1.1*0x10000))
cur_pen = freetype.Vector()
pen_translate = freetype.Vector()
for cur_char in text:
self._face.set_transform(matrix, pen_translate)
self._face.load_char(cur_char)
kerning = self._face.get_kerning(prev_char, cur_char)
pen.x += kerning.x
slot = self._face.glyph
bitmap = slot.bitmap
cur_pen.x = pen.x
cur_pen.y = pen.y - slot.bitmap_top * 64
self.draw_ft_bitmap(image, bitmap, cur_pen, color)
pen.x += slot.advance.x
prev_char = cur_char
return image
显示每个汉字的位图数据。
def draw_ft_bitmap(self, img, bitmap, pen, color):
'''
draw each char
:param bitmap: bitmap
:param pen: pen
:param color: pen color e.g.(0,0,255) - red
:return: image
'''
x_pos = pen.x >> 6
y_pos = pen.y >> 6
cols = bitmap.width
rows = bitmap.rows
glyph_pixels = bitmap.buffer
for row in range(rows):
for col in range(cols):
if glyph_pixels[row*cols + col] != 0:
img[y_pos + row,x_pos + col] = color
https://blog.csdn.net/caimouse/article/details/51749579
转载：https://blog.csdn.net/caimouse/article/details/102525550