通过 Python 把图片转换为 ASCII art，好玩！

相信很多人都知道 ASCII art，这是一种使用可打印 ASCII 字符集来构图的图形设计技术。这种艺术最简单的形式就是表情符号，例如:-) 或 :-3，今天我们就来制作更为复杂的图像

image 的本质

首先，我们先来阐明下图像在计算机系统中的表示方式。图片通常以 .png 或 .jpg 等格式存储在磁盘上，所有这些文件类型都具有相似的结构：它们大致由标题和数据部分组成，前者存储有关图像的有用信息，例如其格式签名，而后者存储实际的像素数据

我们看到的图像实际由像素组成，像素是我们都熟悉的光栅图像中最小的可寻址元素，它们通常表示为一组通道，也称为颜色。在最常见的颜色值中，有经典的 RGB（红绿蓝）和 RGBA（红绿蓝 Alpha）。两者之间的区别在于后者有一个额外的通道，称为“alpha”，用于指定图像的不透明度。

RGBA 是我们将要使用的，因为它也可以用来表示空背景

将 pixels 转换为 ASCCII

现在我们已经了解了图像的表示方式，接下来讨论如何将像素转换为实际的 ASCII 字符

要理解这一点，我们首先看一下像素颜色强度，该值是指所有像素通道的总和除以通道可以具有的最大值的总和（在本例中为 255）

# Import types for clarity
from typing import NewType, Tuple

# Maximum value the sum of the pixel's channel values can reach
MAX_CHANNEL_VALUES = 255 * 4

# Defining an RGBA pixel type as a tuple of 4 integers
Pixel = NewType("Pixel", Tuple[int, int, int, int])

# Returns the pixel's intensity value as a float
def get_pixel_intensity(pixel: Pixel) -> float:
    # Sum of the pixel's channel values divided by the maximum possible intensity 
    return sum(pixel) / MAX_CHANNEL_VALUES

为了清晰起见，我们在第一行导入了静态类型

在上述代码中，我们定义了一个新的 Pixel 类型，一个由四个整数组成的元组，每个整数代表一个 RGBA 像素中的一个通道。然后我们又定义了一个函数来提取给定像素的强度，首先将所有通道值相加，然后将结果除以像素通道可以达到的最大值，从而有效地获得强度百分比。

一旦我们计算了像素的强度，就可以将其映射到 ASCII 字符。为此，我们必须定义一个用于表示像素的字符集

# Character set for out ASCII arts
CHARACTERS = (' ', '.', '°', '*', 'o', 'O', '#', '@')

# Restuns the character that corresponds to the given pixel intensity
def map_intensity_to_character(intensity: float) -> CHARACTERS:
    return CHARACTERS[round(intensity * len(CHARACTERS))]

字符集的顺序是从空格到@，这意味着像素越密集，其对应的 ASCII 字符占用的空间就越多

该函数将给定的像素强度映射到集合中的一个字符，强度 * len(CHARACTERS) 的结果四舍五入，因为索引必须是整数

现在，让我们用一个简单的脚本将这些代码片段组合在一起

# Import an image library for the sake of simplicity
from PIL import Image
# Import argv for command line arguments
from sys import argv

# Transforms an image into a string of ASCII characters
def convert_image(image: Image) -> str:
  ascii_string = '' 
  # Iterate over every pixel of the image 
  for pixel in image.getdata():
    intensity = get_pixel_intensity(pixel)
    character = map_intensity_to_character(intensity)
    ascii_string += character
  return ascii_string

def main():
  # Get the image name from the command line arguments list
  image_name = argv[1]
  # Open the image file using the PIL image library
  image = Image.open(image_name)
  # Convert the image to a string of ASCII characters
  ascii_image = convert_image(image)

if __name__ == '__main__':
  main()

查看 ASCII

一旦我们获得了图像 ASCII 字符串的表示方法，接下来就是通过一种以图形方式查看它的方法，最简单的方法就是将其打印到控制台。由于图像通常按像素行组织，因此在打印它们时，我们也必须相应地使用换行符

在这里，我们编写了一个简单的函数，将 ASCII 打印到控制台以及如何从主函数调用

# Prints the given ASCII art
# size is a Tuple containing the width and height of the image
def print_ascii_art(size: Tuple[int, int], characters: str):
  index = 0 
  # Iterate over all the rows of the image 
  for _ in range(size[1]):
    # Print a number of characters equal to the width of the image 
    # from the ascii string 
    print(characters[index:index+size[0]])
    index += size[0]

def main():
  image_name = argv[1]
  image = Image.open(image_name)
  ascii_image = convert_image(image)
  # Actually print the ASCII image to the console
  print_ascii_art(image.size, ascii_image)

我们先转换一张简单的图片

python converter.py image.png

Output:

可以看到，图像还是有些失真，我们再进行下优化

使用 HTML 来展示转换后的图像

# The starting point of the generated HTML file
HTML_TEMPLATE = """
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>ASCII Art</title>
</head>
<body>
    <div style="background-color: black; color: white;">
        <pre>{}</pre>
    </div>
</body>
</html>
"""

def ascii_image_to_html(image_name: str, characters: str, size: Tuple[int, int]):
  # Open an HTML file for writing with the '.html' extension 
  with open(image_name + '.html', 'w') as image_file:
    ascii_image = ''    
    index = 0 
    # Generate the ASCII image as explained before 
    for _ in range(size[1]):
      # Manually add a newline character at the end of each row or characters
      ascii_image += characters[index:index+size[0]] + '\n'
      index += size[0]
    # Finally write the ASCII string to the HTML file using the template  
    image_file.write(HTML_TEMPLATE.format(ascii_image))

def main():
  image_name = argv[1]
  image = Image.open(image_name)
  ascii_image = convert_image(image)
  # Save the result in an HTML file
  ascii_image_to_html(image_name, ascii_image, image.size)

下面就来看看不同图片转换成 ASCII 之后的效果吧

下面是完整代码

#!/usr/bin/env python3
from typing import Tuple, NewType
from PIL import Image
from sys import argv


Pixel = NewType("Pixel", Tuple[int, int, int, int])

CHARACTERS = (' ', '.', '°', '*', 'o', 'O', '#', '@')

MAX_CHANNEL_INTENSITY = 255
MAX_CHANNEL_VALUES = MAX_CHANNEL_INTENSITY * 4 # 4 is the number of channels of a Pixel

HTML_TEMPLATE = """
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>ASCII Art</title>
</head>
<body>
    <div style="background-color: black; color: white; line-height: 10px">
        <pre>{}</pre>
    </div>
</body>
</html>
"""


def map_intensity_to_character(intensity: float) -> CHARACTERS:
    return CHARACTERS[round(intensity * len(CHARACTERS))]


def get_pixel_intensity(pixel: Pixel) -> float:
    return sum(pixel) / 1020 # 1020 = 255 * 4


def print_ascii_art(size: Tuple[int, int], characters: str):
    index = 0 
    for _ in range(size[1]):
        print(characters[index:index+size[0]])
        index += size[0]


def ascii_image_to_html(image_name: str, characters: str, size: Tuple[int, int]):
    with open(image_name + '.html', 'w') as image_file:
        ascii_image = ''    
        index = 0 
        for _ in range(size[1]):
            ascii_image += characters[index:index+size[0]] + '\n'
            index += size[0]
        image_file.write(HTML_TEMPLATE.format(ascii_image))


def convert_image(image: Image) -> str:
    ascii_string = '' 
    for pixel in image.getdata():
        intensity = get_pixel_intensity(pixel)
        character = map_intensity_to_character(intensity)
        ascii_string += character
    return ascii_string


def main() -> None:

    image_name = argv[1]
    image = Image.open(image_name)

    print(image.size, image.mode, image.size, image.getcolors())

    ascii_image = convert_image(image)

    #print_ascii_art(image.size, ascii_image)

    ascii_image_to_html(image_name, ascii_image, image.size)


if __name__ == '__main__':
    main()

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原文地址：https://towardsdatascience.com/convert-pictures-to-ascii-art-ece89582d65b往期推荐