Python2.x上使用freetype实现OpenCV2.x的中文输出

OpenCV2.x的putText是无法处理中文的（OpenCV3.x中集成了freetype实现中文输出），同样，Python2.x对中文的支持也很差（同样这一情况在Python3.x中得到了改善）。
所以最方便的方法是，两个都换成3.x版本的。。。[捂脸]

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freetype的安装

计算机上显示文本的过程大体上是，先将文本转换成一个一个的bitmap，然后再用图形系统将这些bitmap显示出来。freetype是一个开源的字体引擎，它完成的工作即是将字符转换成bitmap。

参考这篇文章和Github项目介绍，首先需要编译安装freetype2
1）到这里下载最新的freetype2，解压缩后进入目录

../configure
make
sudo make install

2）到这里下载freetype-py源代码，解压缩后进入目录

sudo ./setup.py install

这样就算安装好了

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Python2.x中文编码的处理

推荐这篇文章
归纳起来就是：Python2.x里有两种字符串类型（str和unicode），可以类比c++里的char和wchar_t
两者可以通过 decode 和 encode 互转

此外需要注意的是，编码正常情况下 print 会打印正确的字符，但pdb观察该变量则是转义符组成的值。这是内部机制的问题，只要print正确就好了

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代码封装

建议使用 wqy-zenhei.ttc，测试了freetype自带的 Vera.ttf 和 windows下的 msyh.ttf，部分中文还是会乱码

算法核心参考这篇文章

#! /usr/bin/env python
# -*- coding: utf-8 -*-

'''
##################################################
# tools                                          #
#------------------------------------------------#
# draw chinese text using freetype on python2.x  #                  #
# 2017.4.12                                      #
##################################################
'''

import numpy as np
import freetype
import copy
import pdb

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

        #descender = metrics.descender/64.0
        #height = metrics.height/64.0
        #linegap = height - ascender + descender
        ypos = int(ascender)

        if not isinstance(text, unicode):
            text = text.decode('utf-8')
        img = self.draw_string(image, pos[0], pos[1]+ypos, text, text_color)
        return img

    def draw_string(self, img, x_pos, y_pos, text, color):
        '''
        draw string
        :param x_pos: text x-postion on img
        :param y_pos: text y-postion on img
        :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)*0x10000L, int(0.2*0x10000L),\
                                 int(0.0*0x10000L), int(1.1*0x10000L))
        cur_pen = freetype.Vector()
        pen_translate = freetype.Vector()

        image = copy.deepcopy(img)
        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][0] = color[0]
                    img[y_pos + row][x_pos + col][1] = color[1]
                    img[y_pos + row][x_pos + col][2] = color[2]


if __name__ == '__main__':
    # just for test
    import cv2
    file = open('class.txt','r')
    line = file.readline()
    img = np.zeros([300,300,3])

    color_ = (0,255,0)
    pos = (3, 3)
    text_size = 24

    ft = put_chinese_text('wqy-zenhei.ttc')
    image = ft.draw_text(img, pos, line, text_size, color_)

    cv2.imshow('ss', image)
    cv2.waitKey(0)

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