custom_captcha_image.py

#!/usr/bin/env python
#coding=utf-8
"""
Created on Sun, 5 May 2019
@author: Nano Zhou
- revise on captcha.image (system file) and customize for target web styles
"""

import os
import random
from PIL import Image, ImageFilter
from PIL.ImageDraw import Draw
from PIL.ImageFont import truetype
try:
    from cStringIO import StringIO as BytesIO
except ImportError:
    from io import BytesIO


FONTS_DIR = os.path.join(os.path.abspath(os.path.dirname(__file__)), 'fonts')
DEFAULT_FONTS = [os.path.join(FONTS_DIR, 'DroidSansMono.ttf')]


table  =  []
for  i  in  range( 256 ):
    table.append( i * 1.97 )


class _Captcha():
    def generate(self, chars, format='png'):
        """Generate an Image Captcha of the given characters.

        :param chars: text to be generated.
        :param format: image file format
        """
        im = self.generate_image(chars)  # work as interface
        out = BytesIO()
        im.save(out, format=format)  # inverse process: Image.open(out)
        out.seek(0)  # Change the stream position to the given byte offset
        return out

    def write(self, chars, output, format='png'):
        """Generate and write an image CAPTCHA data to the output.

        :param chars: text to be generated.
        :param output: output destination.
        :param format: image file format
        """
        im = self.generate_image(chars)
        return im.save(output, format=format)


class ImageCaptcha(_Captcha):
    """Create an image CAPTCHA.

    ImageCaptcha has one built-in font, DroidSansMono, which is licensed under
    Apache License 2. You should always use your own fonts::

        captcha = ImageCaptcha(fonts=['/path/to/A.ttf', '/path/to/B.ttf'])

    You can put as many fonts as you like. But be aware of your memory, all of
    the fonts are loaded into your memory, so keep them a lot, but not too
    many.

    :param width: The width of the CAPTCHA image.
    :param height: The height of the CAPTCHA image.
    :param fonts: Fonts to be used to generate CAPTCHA images.
    :param font_sizes: Random choose a font size from this parameters.
    """
    def __init__(self, width=160, height=60, fonts=None, font_sizes=None):
        self._width = width
        self._height = height
        self._fonts = fonts or DEFAULT_FONTS
        self._font_sizes = font_sizes
        self._truefonts = []

    @property  # convert method to read-only property
    def truefonts(self):
        if self._truefonts:
            return self._truefonts
        self._truefonts = tuple([
            truetype(n, s)
            for n in self._fonts
            for s in self._font_sizes
        ])
        return self._truefonts

    @staticmethod
    def create_noise_curve(image, color):
        w, h = image.size
        x1 = random.randint(0, int(w / 5))
        x2 = random.randint(w - int(w / 5), w)
        y1 = random.randint(int(h / 5), h - int(h / 5))
        y2 = random.randint(y1, h - int(h / 5))
        points = [x1, y1, x2, y2]
        end = random.randint(160, 200)
        start = random.randint(0, 20)  # start, end: angle in degrees
        Draw(image).arc(points, start, end, fill=color)
        return image

    @staticmethod
    def create_noise_dots(image, color, width=3, number=30):
        draw = Draw(image)
        w, h = image.size
        while number:
            x1 = random.randint(0, w)
            y1 = random.randint(0, h)
            draw.line(((x1, y1), (x1 - 1, y1 - 1)), fill=color, width=width)
            number -= 1
        return image

    def create_captcha_image(self, chars, color, background):
        """Create the CAPTCHA image itself.

        :param chars: text to be generated.
        :param color: color of the text.
        :param background: color of the background.

        The color should be a tuple of 3 numbers, such as (0, 255, 255).
        """
        image = Image.new('RGB', (self._width, self._height), background)  # 3x8-bit pixels, true color
        draw = Draw(image)

        def _draw_character(c):
            font = random.choice(self.truefonts)
            w, h = draw.textsize(c, font=font)  # h > w in textsize

            dx = random.randint(0, 4)
            dy = random.randint(0, 6)
            im = Image.new('RGBA', (w + dx, h + dy))  # 4x8-bit pixels, true color with transparency mask
            Draw(im).text((dx, dy), c, font=font, fill=color)  #  Top left corner of the text (dx, dy)

            # rotate
            im = im.crop(im.getbbox())  # Calculates the bounding box of the non-zero regions in the image
            im = im.rotate(random.uniform(-10, 10), Image.BILINEAR, expand=1)
            
            # warp (transformation)
            dx = w * random.uniform(0.1, 0.3)
            dy = h * random.uniform(0.2, 0.3)
            x1 = int(random.uniform(-dx, dx))
            y1 = int(random.uniform(-dy, dy))
            x2 = int(random.uniform(-dx, dx))
            y2 = int(random.uniform(-dy, dy))
            w2 = w + abs(x1) + abs(x2)
            h2 = h + abs(y1) + abs(y2)
            data = (
                x1, y1,
                -x1, h2 - y2,
                w2 + x2, h2 + y2,
                w2 - x2, -y1,
            )
            im = im.resize((w2, h2))
            im = im.transform((w, h), Image.QUAD, data)
            return im

        images = []
        for c in chars:
            if random.random() > 0.5:
                images.append(_draw_character(" "))
            images.append(_draw_character(c))
            

        text_width = sum([im.size[0] for im in images])

        width = max(text_width, self._width)
        image = image.resize((width, self._height))

        average = int(text_width / len(chars))
        rand = int(0.25 * average)
        offset = int(average * 0.1)

        for im in images:
            w, h = im.size
            mask = im.convert('L').point(table)  # Maps this image through a lookup table or function
            image.paste(im, (offset, int((self._height - h) / 2)), mask)  # If a 2-tuple is used instead, it’s treated as the upper left corner.
            offset = offset + w + random.randint(-rand, 0)

        if width > self._width:
            image = image.resize((self._width, self._height))

        return image

    def generate_image(self, chars):
        """Generate the image of the given characters.

        :param chars: text to be generated.
        """
        background = random_color(238, 255)
        color = random_color(10, 200, random.randint(220, 255))
        im = self.create_captcha_image(chars, color, background)
        self.create_noise_dots(im, color, width=1, number=5)  # add small noise
        self.create_noise_curve(im, color)
        im = im.filter(ImageFilter.SMOOTH)
        return im


def random_color(start, end, opacity=None):
    red = random.randint(start, end)
    green = random.randint(start, end)
    blue = random.randint(start, end)
    if opacity is None:
        return (red, green, blue)
    return (red, green, blue, opacity)