def to_bitmap(self, color_dict=None):
        """Returns a valid bitmap list that represents each frame of the clip.
        If `color_dict` is not specified, then it will use the same `color_dict`
        that was used to create the clip.
        """
        color_dict = color_dict or self.color_dict

        bitmap = []
        for frame in self.iter_frames():
            bitmap.append([])
            for line in frame:
                bitmap[-1].append("")
                for pixel in line:
                    letter = list(color_dict.keys())[
                        list(color_dict.values()).index(tuple(pixel))
                    ]
                    bitmap[-1][-1] += letter

        return bitmap
Returns a valid bitmap list that represents each frame of the clip.
        If `color_dict` is not specified, then it will use the same `color_dict`
        that was used to create the clip.
        
moviepy/video/VideoClip.py