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
网络异常，图片无法展示
|
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()
