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"""
Portable Network Graphics (PNG) file format
Official spec: http://www.w3.org/TR/PNG
Original code contributed by Robin Munn (rmunn at pobox dot com)
(although the code has been extensively reorganized to meet Construct's
coding conventions)
"""
from construct_legacy import *
#===============================================================================
# utils
#===============================================================================
def Coord(name, field=UBInt8):
return Struct(name,
field("x"),
field("y"),
)
compression_method = Enum(UBInt8("compression_method"),
deflate = 0,
_default_ = Pass
)
#===============================================================================
# 11.2.3: PLTE - Palette
#===============================================================================
plte_info = Struct("plte_info",
Value("num_entries", lambda ctx: ctx._.length / 3),
Array(lambda ctx: ctx.num_entries,
Struct("palette_entries",
UBInt8("red"),
UBInt8("green"),
UBInt8("blue"),
),
),
)
#===============================================================================
# 11.2.4: IDAT - Image data
#===============================================================================
idat_info = OnDemand(
Field("idat_info", lambda ctx: ctx.length),
)
#===============================================================================
# 11.3.2.1: tRNS - Transparency
#===============================================================================
trns_info = Switch("trns_info", lambda ctx: ctx._.image_header.color_type,
{
"greyscale": Struct("data",
UBInt16("grey_sample")
),
"truecolor": Struct("data",
UBInt16("red_sample"),
UBInt16("blue_sample"),
UBInt16("green_sample"),
),
"indexed": Array(lambda ctx: ctx.length,
UBInt8("alpha"),
),
}
)
#===============================================================================
# 11.3.3.1: cHRM - Primary chromacities and white point
#===============================================================================
chrm_info = Struct("chrm_info",
Coord("white_point", UBInt32),
Coord("red", UBInt32),
Coord("green", UBInt32),
Coord("blue", UBInt32),
)
#===============================================================================
# 11.3.3.2: gAMA - Image gamma
#===============================================================================
gama_info = Struct("gama_info",
UBInt32("gamma"),
)
#===============================================================================
# 11.3.3.3: iCCP - Embedded ICC profile
#===============================================================================
iccp_info = Struct("iccp_info",
CString("name"),
compression_method,
Field("compressed_profile",
lambda ctx: ctx._.length - (len(ctx.name) + 2)
),
)
#===============================================================================
# 11.3.3.4: sBIT - Significant bits
#===============================================================================
sbit_info = Switch("sbit_info", lambda ctx: ctx._.image_header.color_type,
{
"greyscale": Struct("data",
UBInt8("significant_grey_bits"),
),
"truecolor": Struct("data",
UBInt8("significant_red_bits"),
UBInt8("significant_green_bits"),
UBInt8("significant_blue_bits"),
),
"indexed": Struct("data",
UBInt8("significant_red_bits"),
UBInt8("significant_green_bits"),
UBInt8("significant_blue_bits"),
),
"greywithalpha": Struct("data",
UBInt8("significant_grey_bits"),
UBInt8("significant_alpha_bits"),
),
"truewithalpha": Struct("data",
UBInt8("significant_red_bits"),
UBInt8("significant_green_bits"),
UBInt8("significant_blue_bits"),
UBInt8("significant_alpha_bits"),
),
}
)
#===============================================================================
# 11.3.3.5: sRGB - Standard RPG color space
#===============================================================================
srgb_info = Struct("srgb_info",
Enum(UBInt8("rendering_intent"),
perceptual = 0,
relative_colorimetric = 1,
saturation = 2,
absolute_colorimetric = 3,
_default_ = Pass,
),
)
#===============================================================================
# 11.3.4.3: tEXt - Textual data
#===============================================================================
text_info = Struct("text_info",
CString("keyword"),
Field("text", lambda ctx: ctx._.length - (len(ctx.keyword) + 1)),
)
#===============================================================================
# 11.3.4.4: zTXt - Compressed textual data
#===============================================================================
ztxt_info = Struct("ztxt_info",
CString("keyword"),
compression_method,
OnDemand(
Field("compressed_text",
# As with iCCP, length is chunk length, minus length of
# keyword, minus two: one byte for the null terminator,
# and one byte for the compression method.
lambda ctx: ctx._.length - (len(ctx.keyword) + 2),
),
),
)
#===============================================================================
# 11.3.4.5: iTXt - International textual data
#===============================================================================
itxt_info = Struct("itxt_info",
CString("keyword"),
UBInt8("compression_flag"),
compression_method,
CString("language_tag"),
CString("translated_keyword"),
OnDemand(
Field("text",
lambda ctx: ctx._.length - (len(ctx.keyword) +
len(ctx.language_tag) + len(ctx.translated_keyword) + 5),
),
),
)
#===============================================================================
# 11.3.5.1: bKGD - Background color
#===============================================================================
bkgd_info = Switch("bkgd_info", lambda ctx: ctx._.image_header.color_type,
{
"greyscale": Struct("data",
UBInt16("background_greyscale_value"),
Alias("grey", "background_greyscale_value"),
),
"greywithalpha": Struct("data",
UBInt16("background_greyscale_value"),
Alias("grey", "background_greyscale_value"),
),
"truecolor": Struct("data",
UBInt16("background_red_value"),
UBInt16("background_green_value"),
UBInt16("background_blue_value"),
Alias("red", "background_red_value"),
Alias("green", "background_green_value"),
Alias("blue", "background_blue_value"),
),
"truewithalpha": Struct("data",
UBInt16("background_red_value"),
UBInt16("background_green_value"),
UBInt16("background_blue_value"),
Alias("red", "background_red_value"),
Alias("green", "background_green_value"),
Alias("blue", "background_blue_value"),
),
"indexed": Struct("data",
UBInt16("background_palette_index"),
Alias("index", "background_palette_index"),
),
}
)
#===============================================================================
# 11.3.5.2: hIST - Image histogram
#===============================================================================
hist_info = Array(lambda ctx: ctx._.length / 2,
UBInt16("frequency"),
)
#===============================================================================
# 11.3.5.3: pHYs - Physical pixel dimensions
#===============================================================================
phys_info = Struct("phys_info",
UBInt32("pixels_per_unit_x"),
UBInt32("pixels_per_unit_y"),
Enum(UBInt8("unit"),
unknown = 0,
meter = 1,
_default_ = Pass
),
)
#===============================================================================
# 11.3.5.4: sPLT - Suggested palette
#===============================================================================
def splt_info_data_length(ctx):
if ctx.sample_depth == 8:
entry_size = 6
else:
entry_size = 10
return (ctx._.length - len(ctx.name) - 2) / entry_size
splt_info = Struct("data",
CString("name"),
UBInt8("sample_depth"),
Array(lambda ctx: splt_info_data_length,
IfThenElse("table", lambda ctx: ctx.sample_depth == 8,
# Sample depth 8
Struct("table",
UBInt8("red"),
UBInt8("green"),
UBInt8("blue"),
UBInt8("alpha"),
UBInt16("frequency"),
),
# Sample depth 16
Struct("table",
UBInt16("red"),
UBInt16("green"),
UBInt16("blue"),
UBInt16("alpha"),
UBInt16("frequency"),
),
),
),
)
#===============================================================================
# 11.3.6.1: tIME - Image last-modification time
#===============================================================================
time_info = Struct("data",
UBInt16("year"),
UBInt8("month"),
UBInt8("day"),
UBInt8("hour"),
UBInt8("minute"),
UBInt8("second"),
)
#===============================================================================
# chunks
#===============================================================================
default_chunk_info = OnDemand(
HexDumpAdapter(Field(None, lambda ctx: ctx.length))
)
chunk = Struct("chunk",
UBInt32("length"),
String("type", 4),
Switch("data", lambda ctx: ctx.type,
{
"PLTE" : plte_info,
"IEND" : Pass,
"IDAT" : idat_info,
"tRNS" : trns_info,
"cHRM" : chrm_info,
"gAMA" : gama_info,
"iCCP" : iccp_info,
"sBIT" : sbit_info,
"sRGB" : srgb_info,
"tEXt" : text_info,
"zTXt" : ztxt_info,
"iTXt" : itxt_info,
"bKGD" : bkgd_info,
"hIST" : hist_info,
"pHYs" : phys_info,
"sPLT" : splt_info,
"tIME" : time_info,
},
default = default_chunk_info,
),
UBInt32("crc"),
)
image_header_chunk = Struct("image_header",
UBInt32("length"),
Magic(b"IHDR"),
UBInt32("width"),
UBInt32("height"),
UBInt8("bit_depth"),
Enum(UBInt8("color_type"),
greyscale = 0,
truecolor = 2,
indexed = 3,
greywithalpha = 4,
truewithalpha = 6,
_default_ = Pass,
),
compression_method,
Enum(UBInt8("filter_method"),
# "adaptive filtering with five basic filter types"
adaptive5 = 0,
_default_ = Pass,
),
Enum(UBInt8("interlace_method"),
none = 0,
adam7 = 1,
_default_ = Pass,
),
UBInt32("crc"),
)
#===============================================================================
# the complete PNG file
#===============================================================================
png_file = Struct("png",
Magic(b"\x89PNG\r\n\x1a\n"),
image_header_chunk,
Rename("chunks", GreedyRange(chunk)),
)
|
