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# -*- coding: utf-8 -*-
# -----------------------------------------------------------------------------
# Copyright (c) Vispy Development Team. All Rights Reserved.
# Distributed under the (new) BSD License. See LICENSE.txt for more info.
# -----------------------------------------------------------------------------
# Author: Luke Campagnola
# -----------------------------------------------------------------------------
import struct
import zlib
import numpy as np
def _make_png(data, level=6):
"""Convert numpy array to PNG byte array.
Parameters
----------
data : numpy.ndarray
Data must be (H, W, 3 | 4) with dtype = np.ubyte (np.uint8)
level : int
https://docs.python.org/2/library/zlib.html#zlib.compress
An integer from 0 to 9 controlling the level of compression:
* 1 is fastest and produces the least compression,
* 9 is slowest and produces the most.
* 0 is no compression.
The default value is 6.
Returns
-------
png : array
PNG formatted array
"""
# Eventually we might want to use ext/png.py for this, but this
# routine *should* be faster b/c it's specialized for our use case
def mkchunk(data, name):
if isinstance(data, np.ndarray):
size = data.nbytes
else:
size = len(data)
chunk = np.empty(size + 12, dtype=np.ubyte)
chunk.data[0:4] = np.array(size, '>u4').tobytes()
chunk.data[4:8] = name.encode('ASCII')
chunk.data[8:8 + size] = data
# and-ing may not be necessary, but is done for safety:
# https://docs.python.org/3/library/zlib.html#zlib.crc32
chunk.data[-4:] = np.array(zlib.crc32(chunk[4:-4]) & 0xffffffff,
'>u4').tobytes()
return chunk
if data.dtype != np.ubyte:
raise TypeError('data.dtype must be np.ubyte (np.uint8)')
dim = data.shape[2] # Dimension
if dim not in (3, 4):
raise TypeError('data.shape[2] must be in (3, 4)')
# www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.IHDR
if dim == 4:
ctyp = 0b0110 # RGBA
else:
ctyp = 0b0010 # RGB
# www.libpng.org/pub/png/spec/1.2/PNG-Structure.html
header = b'\x89PNG\x0d\x0a\x1a\x0a' # header
h, w = data.shape[:2]
depth = data.itemsize * 8
ihdr = struct.pack('!IIBBBBB', w, h, depth, ctyp, 0, 0, 0)
c1 = mkchunk(ihdr, 'IHDR')
# www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.IDAT
# insert filter byte at each scanline
idat = np.empty((h, w * dim + 1), dtype=np.ubyte)
idat[:, 1:] = data.reshape(h, w * dim)
idat[:, 0] = 0
comp_data = zlib.compress(idat, level)
c2 = mkchunk(comp_data, 'IDAT')
c3 = mkchunk(np.empty((0,), dtype=np.ubyte), 'IEND')
# concatenate
lh = len(header)
png = np.empty(lh + c1.nbytes + c2.nbytes + c3.nbytes, dtype=np.ubyte)
png.data[:lh] = header
p = lh
for chunk in (c1, c2, c3):
png[p:p + len(chunk)] = chunk
p += chunk.nbytes
return png
def read_png(filename):
"""Read a PNG file to RGB8 or RGBA8
Requires Pillow.
Parameters
----------
filename : str
File to read.
Returns
-------
data : array
Image data.
See also
--------
write_png, imread, imsave
"""
try:
from PIL import Image
x = Image.open(filename)
try:
y = np.asarray(x)
y = np.array([yy for yy in y], np.uint8)
finally:
x.close()
return y
except ImportError:
raise RuntimeError("read_png requires the Pillow package.")
def write_png(filename, data):
"""Write a PNG file
Unlike imsave, this requires no external dependencies.
Parameters
----------
filename : str
File to save to.
data : array
Image data.
See also
--------
read_png, imread, imsave
"""
data = np.asarray(data)
if not data.ndim == 3 and data.shape[-1] in (3, 4):
raise ValueError('data must be a 3D array with last dimension 3 or 4')
with open(filename, 'wb') as f:
f.write(_make_png(data)) # Save array with make_png
def imread(filename, format=None):
"""Read image data from disk
Requires imageio or PIL.
Parameters
----------
filename : str
Filename to read.
format : str | None
Format of the file. If None, it will be inferred from the filename.
Returns
-------
data : array
Image data.
See also
--------
imsave, read_png, write_png
"""
imageio, PIL = _check_img_lib()
if imageio is not None:
return imageio.imread(filename, format)
elif PIL is not None:
im = PIL.Image.open(filename)
if im.mode == 'P':
im = im.convert()
# Make numpy array
a = np.asarray(im)
if len(a.shape) == 0:
raise MemoryError("Too little memory to convert PIL image to "
"array")
return a
else:
raise RuntimeError("imread requires the imageio or PIL package.")
def imsave(filename, im, format=None):
"""Save image data to disk
Requires imageio or PIL.
Parameters
----------
filename : str
Filename to write.
im : array
Image data.
format : str | None
Format of the file. If None, it will be inferred from the filename.
See also
--------
imread, read_png, write_png
"""
# Import imageio or PIL
imageio, PIL = _check_img_lib()
if imageio is not None:
return imageio.imsave(filename, im, format)
elif PIL is not None:
pim = PIL.Image.fromarray(im)
pim.save(filename, format)
else:
raise RuntimeError("imsave requires the imageio or PIL package.")
def _check_img_lib():
"""Utility to search for imageio or PIL"""
# Import imageio or PIL
imageio = PIL = None
try:
import imageio
except ImportError:
try:
import PIL.Image
except ImportError:
pass
return imageio, PIL
|
