ASCII：一个简单的字符编码方案

pillow模块：读取图像，访问底层数据
numpy模块：计算平均值

import sys, random, argparse
import numpy as np
import math
from PIL import Image

定义灰度等级和网格

定义两种灰度等级作为全局值，用于将亮度值转换为ASCII 字符

从最黑暗变到最亮

# 70 levels of gray
gscale1 = "$@B%8&WM#*oahkbdpqwmZO0QLCJUYXzcvunxrjft/\|()1{}[]?-_+~<>i!lI;:,\"^`'. "

# 10 levels of gray
gscale2 = '@%#*+=-:. '

http://paulbourke.net/dataformats/asciiart/

准备图像，并分割成网格

cols = 80
scale = 0.43

# open the image and convert to grayscale
image = Image.open('youling.png').convert("L")
# store the image dimensions  # image.size
W, H = image.size[0], image.size[1]
# compute the tile width  根据用户给定列数（cols）计算每个网格的宽度
w = W/cols
# compute the tile height based on the aspect ratio and scale of the font
h = w/scale
# compute the number of rows to use in the final grid
rows = int(H/h)

w网格的宽 = W图片的宽 / cols列数
h网格的高度 = w网格的宽 / 垂直比例系数scale
rows行 总共有多少行

Pillow模块里的convert()函数可以将图像从一种模式转换为另一种模式
convert(‘L’)将原始图像转换为灰度图像 L is luminance：是图像亮度的单位
convert(‘1’)将原始图像转换为黑白模式
convert(‘P’, palette=Image.ADAPTIVE, colors=1)将原始图像转换为使用颜色调色板的单色模式,colors=2，图片只有2种颜色
还有RGB、RGBA，CMYK，LAB，HSV，YCbCr、XYZ等等模式

CMYK代表青、洋红、黄和黑色，是一种用于印刷的颜色模式。它是印刷过程中使用的四种油墨颜色的缩写，包括青色（Cyan）、洋红色（Magenta）、黄色（Yellow）和黑色（Key），通过它们的不同组合可以得到各种颜色和色调。相对于RGB颜色模式（红、绿、蓝），CMYK颜色模式更适合印刷。

计算平均亮度

计算灰度图像中每一小块的平均亮度

def getAverageL(image):
    # get the image as a numpy array
    im = np.array(image)
    # get the dimensions
    w,h = im.shape
    # get the average
    return np.average(im.reshape(w*h))

将 image 转换成一个 numpy数组，此时 im 成为一个二维数组，包含每个像素的亮度

保存该图像的尺寸

numpy.average()计算该图像中的亮度平均值，做法是用 numpy.reshape()先将维度为宽和高(w，h)的二维数组转换成扁平的一维，其长度是宽度乘以高度(w*h)。然后 numpy.average()调用对这些数组值求和并计算平均值

从图像生成 ASCII 内容

# an ASCII image is a list of character strings
aimg = []
# generate the list of tile dimensions
for j in range(rows):
    # 计算每个图像小块的起始和结束 y 坐标
    y1 = int(j*h)
    y2 = int((j+1)*h)
    # correct the last tile
    if j == rows-1:
        y2 = H
    # append an empty string
    aimg.append("")
    for i in range(cols):
        # crop the image to fit the tile
        x1 = int(i*w)
        x2 = int((i+1)*w)
        # correct the last tile
        if i == cols-1:
            x2 = W
        # crop the image to extract the tile into another Image object
        img = image.crop((x1, y1, x2, y2))
        # get the average luminance # 获取网格的平均亮度值
        avg = int(getAverageL(img))
        # look up the ASCII character for grayscale value (avg)
        if moreLevels:
	        # 将平均亮度值[0,255]对用到70级灰度[0,69]
	        gsval = gscale1[int((avg*69)/255)]
	    else:
	        # 将平均亮度值[0,255]对用到10级灰度[0,9]
	        gsval = gscale2[int((avg*9)/255)]
        # append the ASCII character to the string
        aimg[j] += gsval

int((avg69)/255)
if avg = 255，可得int((avg69)/255)=69，在该字符串中最后一个索引是69

命令行选项

接下来，为程序定义一些命令行选项。这段代码使用内置的 argparse 类：

parser = argparse.ArgumentParser(description="descStr")
# add expected arguments
parser.add_argument('--file', dest='imgFile', required=True)
parser.add_argument('--scale', dest='scale', required=False)
parser.add_argument('--out', dest='outFile', required=False)
parser.add_argument('--cols', dest='cols', required=False)
parser.add_argument('--morelevels', dest='moreLevels', action='store_true')

包含指定图像文件输入的选项（唯一必须的参数）
设置垂直比例因子
设置输出文件名
设置 ASCII 输出中的文本列数
添加–morelevels 选项，让用户选择更多层次的灰度梯度

将 ASCII 文本图形字符串写入文本文件

最后，将生成的 ASCII 字符串列表，写入一个文本文件：

# open a new text file
f = open(outFile, 'w')
# write each string in the list to the new file
for row in aimg:
	f.write(row + '\n')
# clean up
f.close()

完整代码

import sys, random, argparse
import numpy as np
import math
from PIL import Image

# 70 levels of gray
gscale1 = "$@B%8&WM#*oahkbdpqwmZO0QLCJUYXzcvunxrjft/\|()1{}[]?-_+~<>i!lI;:,\"^`'. "

# 10 levels of gray
gscale2 = '@%#*+=-:. '

def getAverageL(image):
    # get the image as a numpy array
    im = np.array(image)
    # get the dimensions
    w,h = im.shape
    # get the average
    return np.average(im.reshape(w*h))

def covertImageToAscii(fileName, cols, scale, moreLevels):
    """
    Given Image and dimensions (rows, cols), returns an m*n list of Images
    """
    # declare globals
    global gscale1, gscale2
    # open image and convert to grayscale
    image = Image.open(fileName).convert('L')
    # store the image dimensions
    W, H = image.size[0], image.size[1]
    print("input image dims: %d x %d" % (W, H))
    # compute tile width
    w = W/cols
    # compute tile height based on the aspect ratio and scale of the font
    h = w/scale
    # compute number of rows to use in the final grid
    rows = int(H/h)
    
    print("cols: %d, rows: %d" % (cols, rows))
    print("tile dims: %d x %d" % (w, h))
    
    # check if image size is too small
    if cols > W or rows > H:
        print("Image too small for specified cols!")
        exit(0)
        
    # an ASCII image is a list of character strings
    aimg = []
    # generate the list of tile dimensions
    for j in range(rows):
        # 计算每个图像小块的起始和结束 y 坐标
        y1 = int(j*h)
        y2 = int((j+1)*h)
        # correct the last tile
        if j == rows-1:
            y2 = H
        # append an empty string
        aimg.append("")
        for i in range(cols):
            # crop the image to fit the tile
            x1 = int(i*w)
            x2 = int((i+1)*w)
            # correct the last tile
            if i == cols-1:
                x2 = W
            # crop the image to extract the tile into another Image object
            img = image.crop((x1, y1, x2, y2))
            # get the average luminance # 获取网格的平均亮度值
            avg = int(getAverageL(img))
            # look up the ASCII character for grayscale value (avg)
            if moreLevels:
                # 将平均亮度值[0,255]对用到70级灰度[0,69]
                gsval = gscale1[int((avg*69)/255)]
            else:
                # 将平均亮度值[0,255]对用到10级灰度[0,9]
                gsval = gscale2[int((avg*9)/255)]
            # append the ASCII character to the string
            aimg[j] += gsval
    # return text image
    return aimg

# main() function
def main():
    # create parser
    descStr = "This program converts an image into ASCII art."
    parser = argparse.ArgumentParser(description=descStr)
    # add expected arguments
    parser.add_argument('--file', dest='imgFile', required=True)
    parser.add_argument('--scale', dest='scale', required=False)
    parser.add_argument('--out', dest='outFile', required=False)
    parser.add_argument('--cols', dest='cols', required=False)
    parser.add_argument('--morelevels', dest='moreLevels', action='store_true')
    
    # parse arguments
    args = parser.parse_args()
    
    imgFile = args.imgFile
    # set output file
    outFile = 'out.txt'
    if args.outFile:
        outFile = args.outFile
    # set scale default as 0.43, which suits a Courier font
    scale = 0.43
    if args.scale:
        scale = float(args.scale)
    # set cols
    cols = 80
    if args.cols:
        cols = int(args.cols)
    print('generating ASCII art...')
    # convert image to ASCII text
    aimg = covertImageToAscii(imgFile, cols, scale, args.moreLevels) 
    
    # open a new text file
    f = open(outFile, 'w')
    # write each string in the list to the new file
    for row in aimg:
        f.write(row + '\n')
    # clean up
    f.close()
    print("ASCII art written to %s" % outFile)
    
# call main
if __name__ == '__main__':
    main()

https://github.com/electronut/pp/blob/master/ascii/ascii.py

将完整代码保存到py文件中

打开终端，切换到ascii.py目录

输入下面代码

$ python ascii.py --file data/robot.jpg --cols 100

将 data/robot.jpg 替换为你想使用的图像文件的相对路径

使用vscode打开out.txt文件，使用Ctrl±可以缩小，可以看到全屏，只能看10灰度等级

还可使用notepad查看out.txt文件



–morelevels就是70灰度等级