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"""
Windows/OS2 Bitmap (BMP)
this could have been a perfect show-case file format, but they had to make
it ugly (all sorts of alignment or
"""
from construct import *
#===============================================================================
# pixels: uncompressed
#===============================================================================
def UncompressedRows(subcon, align_to_byte = False):
"""argh! lines must be aligned to a 4-byte boundary, and bit-pixel
lines must be aligned to full bytes..."""
if align_to_byte:
line_pixels = Bitwise(
Aligned(Array(lambda ctx: ctx.width, subcon), modulus = 8)
)
else:
line_pixels = Array(lambda ctx: ctx.width, subcon)
return Array(lambda ctx: ctx.height,
Aligned(line_pixels, modulus = 4)
)
uncompressed_pixels = Switch("uncompressed", lambda ctx: ctx.bpp,
{
1 : UncompressedRows(Bit("index"), align_to_byte = True),
4 : UncompressedRows(Nibble("index"), align_to_byte = True),
8 : UncompressedRows(Byte("index")),
24 : UncompressedRows(
Sequence("rgb", Byte("red"), Byte("green"), Byte("blue"))
),
}
)
#===============================================================================
# pixels: Run Length Encoding (RLE) 8 bit
#===============================================================================
class RunLengthAdapter(Adapter):
def _encode(self, obj):
return len(obj), obj[0]
def _decode(self, obj):
length, value = obj
return [value] * length
rle8pixel = RunLengthAdapter(
Sequence("rle8pixel",
Byte("length"),
Byte("value")
)
)
#===============================================================================
# file structure
#===============================================================================
bitmap_file = Struct("bitmap_file",
# header
Const(String("signature", 2), "BM"),
ULInt32("file_size"),
Padding(4),
ULInt32("data_offset"),
ULInt32("header_size"),
Enum(Alias("version", "header_size"),
v2 = 12,
v3 = 40,
v4 = 108,
),
ULInt32("width"),
ULInt32("height"),
Value("number_of_pixels", lambda ctx: ctx.width * ctx.height),
ULInt16("planes"),
ULInt16("bpp"), # bits per pixel
Enum(ULInt32("compression"),
Uncompressed = 0,
RLE8 = 1,
RLE4 = 2,
Bitfields = 3,
JPEG = 4,
PNG = 5,
),
ULInt32("image_data_size"), # in bytes
ULInt32("horizontal_dpi"),
ULInt32("vertical_dpi"),
ULInt32("colors_used"),
ULInt32("important_colors"),
# palette (24 bit has no palette)
OnDemand(
Array(lambda ctx: 2 ** ctx.bpp if ctx.bpp <= 8 else 0,
Struct("palette",
Byte("blue"),
Byte("green"),
Byte("red"),
Padding(1),
)
)
),
# pixels
OnDemandPointer(lambda ctx: ctx.data_offset,
Switch("pixels", lambda ctx: ctx.compression,
{
"Uncompressed" : uncompressed_pixels,
}
),
),
)
if __name__ == "__main__":
obj = bitmap_file.parse_stream(open("../../../tests/bitmap8.bmp", "rb"))
print (obj)
print (repr(obj.pixels.value))
|
