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# encoding: utf-8
from __future__ import absolute_import, division, print_function
from .constants import MIME_TYPE
from .helpers import LITTLE_ENDIAN, StreamReader
from .image import BaseImageHeader
class Bmp(BaseImageHeader):
"""
Image header parser for BMP images
"""
@classmethod
def from_stream(cls, stream):
"""
Return |Bmp| instance having header properties parsed from the BMP
image in *stream*.
"""
stream_rdr = StreamReader(stream, LITTLE_ENDIAN)
px_width = stream_rdr.read_long(0x12)
px_height = stream_rdr.read_long(0x16)
horz_px_per_meter = stream_rdr.read_long(0x26)
vert_px_per_meter = stream_rdr.read_long(0x2A)
horz_dpi = cls._dpi(horz_px_per_meter)
vert_dpi = cls._dpi(vert_px_per_meter)
return cls(px_width, px_height, horz_dpi, vert_dpi)
@property
def content_type(self):
"""
MIME content type for this image, unconditionally `image/bmp` for
BMP images.
"""
return MIME_TYPE.BMP
@property
def default_ext(self):
"""
Default filename extension, always 'bmp' for BMP images.
"""
return 'bmp'
@staticmethod
def _dpi(px_per_meter):
"""
Return the integer pixels per inch from *px_per_meter*, defaulting to
96 if *px_per_meter* is zero.
"""
if px_per_meter == 0:
return 96
return int(round(px_per_meter * 0.0254))
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