#
# The Python Imaging Library.
# $Id$
#
# SGI image file handling
#
# See "The SGI Image File Format (Draft version 0.97)", Paul Haeberli.
# <ftp://ftp.sgi.com/graphics/SGIIMAGESPEC>
#
#
# History:
# 2017-22-07 mb Add RLE decompression
# 2016-16-10 mb Add save method without compression
# 1995-09-10 fl Created
#
# Copyright (c) 2016 by Mickael Bonfill.
# Copyright (c) 2008 by Karsten Hiddemann.
# Copyright (c) 1997 by Secret Labs AB.
# Copyright (c) 1995 by Fredrik Lundh.
#
# See the README file for information on usage and redistribution.
#
from __future__ import annotations
import os
import struct
from typing import IO
from . import Image, ImageFile
from ._binary import i16be as i16
from ._binary import o8
def _accept(prefix: bytes) -> bool:
return len(prefix) >= 2 and i16(prefix) == 474
MODES = {
(1, 1, 1): "L",
(1, 2, 1): "L",
(2, 1, 1): "L;16B",
(2, 2, 1): "L;16B",
(1, 3, 3): "RGB",
(2, 3, 3): "RGB;16B",
(1, 3, 4): "RGBA",
(2, 3, 4): "RGBA;16B",
}
##
# Image plugin for SGI images.
[docs]
class SgiImageFile(ImageFile.ImageFile):
format = "SGI"
format_description = "SGI Image File Format"
def _open(self) -> None:
# HEAD
assert self.fp is not None
headlen = 512
s = self.fp.read(headlen)
if not _accept(s):
msg = "Not an SGI image file"
raise ValueError(msg)
# compression : verbatim or RLE
compression = s[2]
# bpc : 1 or 2 bytes (8bits or 16bits)
bpc = s[3]
# dimension : 1, 2 or 3 (depending on xsize, ysize and zsize)
dimension = i16(s, 4)
# xsize : width
xsize = i16(s, 6)
# ysize : height
ysize = i16(s, 8)
# zsize : channels count
zsize = i16(s, 10)
# layout
layout = bpc, dimension, zsize
# determine mode from bits/zsize
rawmode = ""
try:
rawmode = MODES[layout]
except KeyError:
pass
if rawmode == "":
msg = "Unsupported SGI image mode"
raise ValueError(msg)
self._size = xsize, ysize
self._mode = rawmode.split(";")[0]
if self.mode == "RGB":
self.custom_mimetype = "image/rgb"
# orientation -1 : scanlines begins at the bottom-left corner
orientation = -1
# decoder info
if compression == 0:
pagesize = xsize * ysize * bpc
if bpc == 2:
self.tile = [
("SGI16", (0, 0) + self.size, headlen, (self.mode, 0, orientation))
]
else:
self.tile = []
offset = headlen
for layer in self.mode:
self.tile.append(
("raw", (0, 0) + self.size, offset, (layer, 0, orientation))
)
offset += pagesize
elif compression == 1:
self.tile = [
("sgi_rle", (0, 0) + self.size, headlen, (rawmode, orientation, bpc))
]
def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
if im.mode not in {"RGB", "RGBA", "L"}:
msg = "Unsupported SGI image mode"
raise ValueError(msg)
# Get the keyword arguments
info = im.encoderinfo
# Byte-per-pixel precision, 1 = 8bits per pixel
bpc = info.get("bpc", 1)
if bpc not in (1, 2):
msg = "Unsupported number of bytes per pixel"
raise ValueError(msg)
# Flip the image, since the origin of SGI file is the bottom-left corner
orientation = -1
# Define the file as SGI File Format
magic_number = 474
# Run-Length Encoding Compression - Unsupported at this time
rle = 0
# Number of dimensions (x,y,z)
dim = 3
# X Dimension = width / Y Dimension = height
x, y = im.size
if im.mode == "L" and y == 1:
dim = 1
elif im.mode == "L":
dim = 2
# Z Dimension: Number of channels
z = len(im.mode)
if dim in {1, 2}:
z = 1
# assert we've got the right number of bands.
if len(im.getbands()) != z:
msg = f"incorrect number of bands in SGI write: {z} vs {len(im.getbands())}"
raise ValueError(msg)
# Minimum Byte value
pinmin = 0
# Maximum Byte value (255 = 8bits per pixel)
pinmax = 255
# Image name (79 characters max, truncated below in write)
filename = os.path.basename(filename)
img_name = os.path.splitext(filename)[0].encode("ascii", "ignore")
# Standard representation of pixel in the file
colormap = 0
fp.write(struct.pack(">h", magic_number))
fp.write(o8(rle))
fp.write(o8(bpc))
fp.write(struct.pack(">H", dim))
fp.write(struct.pack(">H", x))
fp.write(struct.pack(">H", y))
fp.write(struct.pack(">H", z))
fp.write(struct.pack(">l", pinmin))
fp.write(struct.pack(">l", pinmax))
fp.write(struct.pack("4s", b"")) # dummy
fp.write(struct.pack("79s", img_name)) # truncates to 79 chars
fp.write(struct.pack("s", b"")) # force null byte after img_name
fp.write(struct.pack(">l", colormap))
fp.write(struct.pack("404s", b"")) # dummy
rawmode = "L"
if bpc == 2:
rawmode = "L;16B"
for channel in im.split():
fp.write(channel.tobytes("raw", rawmode, 0, orientation))
if hasattr(fp, "flush"):
fp.flush()
[docs]
class SGI16Decoder(ImageFile.PyDecoder):
_pulls_fd = True
[docs]
def decode(self, buffer: bytes) -> tuple[int, int]:
assert self.fd is not None
assert self.im is not None
rawmode, stride, orientation = self.args
pagesize = self.state.xsize * self.state.ysize
zsize = len(self.mode)
self.fd.seek(512)
for band in range(zsize):
channel = Image.new("L", (self.state.xsize, self.state.ysize))
channel.frombytes(
self.fd.read(2 * pagesize), "raw", "L;16B", stride, orientation
)
self.im.putband(channel.im, band)
return -1, 0
#
# registry
Image.register_decoder("SGI16", SGI16Decoder)
Image.register_open(SgiImageFile.format, SgiImageFile, _accept)
Image.register_save(SgiImageFile.format, _save)
Image.register_mime(SgiImageFile.format, "image/sgi")
Image.register_extensions(SgiImageFile.format, [".bw", ".rgb", ".rgba", ".sgi"])
# End of file