Python中将PPM图像转换为ASCII艺术

Question

我需要写一个程序，从命令行读取一个文件，然后把它转换成ASCII艺术。我使用的是PPM格式，这里有一个链接到项目的详细信息。

这是我目前的进展：

import sys

def main(filename):
    image = open(filename)
    #reads through the first three lines
    color = image.readline().splitlines()
    size_width, size_height = image.readline().split()
    max_color = image.readline().splitlines()

    #reads the body of the file
    pixels = image.read().split()
    red = 0
    green = 0
    blue = 0
    r_g_b_value = []
    #pulls out the values of each tuple and coverts it to its grayscale value 
    for i in pixels:
        if i !=  "\n" or " ":
            if len(i) == 3:
                red = int(i[0]) * .3
                green = int(i[1]) * .59
                blue = int(i[2]) * .11
            elif len(i) == 2:
                red == int(i[0]) * .3
                green == int(i[1]) *.59
                blue == 0
            elif len(i) == 1:
                red == int(i[0]) * .3
                green == 0
                blue == 0

            r_g_b_value = [red + green + blue]

            character = []
        for j in len(r_g_b_value):
            if int(j) <= 16:
                character = " "
            elif int(j) > 16 and int(j) <= 32:
                character = "."
            elif int(j) > 32 and int(j) <= 48:
                character = ","
            elif int(j) > 48 and int(j) <= 64:
                charcter = ":"
            elif int(j) > 64 and int(j) <= 80:
                character = ";"
            elif int(j) > 80 and int(j) <= 96:
                character = "+"
            elif int(j) > 96 and int(j) <= 112:
                character = "="
            elif int(j) > 112 and int(j) <= 128:
                character = "o"
            elif int(j) > 128 and int(j) <= 144:
                character = "a"
            elif int(j) > 144 and int(j) <= 160:
                character = "e"
            elif int(j) > 160 and int(j) <= 176:
                character = "0"
            elif int(j) > 176 and int(j) <= 192:
                character = "$"
            elif int(j) > 192 and int(j) <= 208:
                character = "@"
            elif int(j) > 208 and int(j) <= 224:
                character = "A"
            elif int(j) > 224 and int(j) <= 240:
                character = "#"
            else:
                character = "M"

            grayscale = character
            print(grayscale)

main(sys.argv[1])

我遇到了一个错误，提示说'int'对象不可迭代。有没有简单的方法来解决这个问题？还有，如何在打印的时候保持图像的完整性？

最后，我不太确定的是，如何保持图片的宽度和高度。

任何帮助都会非常感谢。

Answer 1

我之前用C#写过一个这样的东西，我用这个公式来计算要使用的字符：

index_into_array = (int)(r_g_b_value * (chars_array_length / (255.0)));

至于宽度和高度，你可以把每两行的垂直像素平均一下，这样就能把高度减半。

编辑1：针对评论的回复：基本的想法是把你的RGB值从0到255的范围缩放到0到数组的长度，然后用这个值作为索引。

编辑2：更新一下，之前我忽略了你的灰度归一化。

Answer 2

这里是你修改过并且可以运行的代码。
虽然它不是最优的，没考虑到头部可能有多或少的注释，也没有处理异常，但这算是一个开始。

import sys
import numpy as np

RGBS = range(16, 255, 16)
CHARS = [' ', '.', ',', ':', ';', '+', '=', 'o',
         'a', 'e', '0', '$', '@', 'A', '#']
FACTORS = [.3, .59, .11]

def main(filename):
    image = open(filename)
    #reads header lines
    color = image.readline()
    _ = image.readline()
    size_width, size_height = image.readline().split()
    max_color = image.readline()

    size_width = int(size_width)
    max_color = int(max_color)

    #reads the body of the file
    data = [int(p) for p in image.read().split()]
    #converts to array and reshape
    data = np.array(data)
    pixels = data.reshape((len(data)/3, 3))
    #calculate rgb value per pixel
    rgbs = pixels * FACTORS
    sum_rgbs = rgbs.sum(axis=1)
    rgb_values = [item * 255 / max_color for item in sum_rgbs]

    grayscales = []
    #pulls out the value of each pixel and coverts it to its grayscale value 
    for indx, rgb_val in enumerate(rgb_values):
        #if max width, new line
        if (indx % size_width) == 0 : grayscales.append('\n')    

        for achar, rgb in zip(CHARS, RGBS):
            if rgb_val <= rgb:
                character = achar
                break
            else:
                character = 'M'

        grayscales.append(character)

    print ''.join(grayscales)

main('test.ppm')

这些是ppm图像和ASCII艺术的结果。

还有我用来做示例的微型ppm文件：

P3
# test.ppm
4 4
15
 0  0  0    0  0  0    0  0  0   15  0 15
 0  0  0    0 15  7    0  0  0    0  0  0
 0  0  0    0  0  0    0 15  7    0  0  0
15  0 15    0  0  0    0  0  0    0  0  0

Answer 3

你可以使用image-to-ansi.py这个脚本来进行转换。

首先，下载image-to-ansi.py：

wget https://gist.githubusercontent.com/klange/1687427/raw/image-to-ansi.py

然后，把它改成Python 3的语法：

2to3 -w image-to-ansi.py

接下来，安装一个叫Pillow的图像库：

pip3 install pillow

把这个脚本保存为ppmimage.py：

# Parses a PPM file and loads it into image-to-ansi.py
import re, itertools, sys
from PIL import Image

image_to_ansi = __import__("image-to-ansi") # __import__ because of minuses in filename. From https://gist.github.com/1687427

if __name__ == '__main__':
    im = Image.open('/dev/stdin')
    for y in range(im.size[1]):
        for x in range(im.size[0]):
            p = im.getpixel((x,y))
            h = "%2x%2x%2x" % (p[0],p[1],p[2])
            short, rgb = image_to_ansi.rgb2short(h)
            sys.stdout.write("\033[48;5;%sm " % short)
        sys.stdout.write("\033[0m\n")
    sys.stdout.write("\n")

你可以这样测试这个脚本（假设你已经安装了netpbm和imagemagick）：

convert -resize $(($COLUMNS*2))x$(($LINES*2)) logo: pnm:- | pnmtoplainpnm | python3 ppmimage.py

在我的电脑上，效果是这样的：