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# Copyright (c) 2016-2020 European Synchrotron Radiation Facility
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"""This module provides basic writing Mulitple-image Network Graphics files.
It only supports RGB888 images of the same shape stored as
MNG-VLC (very low complexity) format.
"""
__authors__ = ["T. Vincent"]
__license__ = "MIT"
__date__ = "15/12/2016"
import logging
import struct
import zlib
import numpy
_logger = logging.getLogger(__name__)
def _png_chunk(name, data):
"""Return a PNG chunk
:param str name: Chunk type
:param byte data: Chunk payload
"""
length = struct.pack(">I", len(data))
name = [char.encode("ascii") for char in name]
chunk = struct.pack("cccc", *name) + data
crc = struct.pack(">I", zlib.crc32(chunk) & 0xFFFFFFFF)
return length + chunk + crc
[docs]
def convert(images, nb_images=0, fps=25):
"""Convert RGB images to MNG-VLC format.
See http://www.libpng.org/pub/mng/spec/
See http://www.libpng.org/pub/png/book/
See http://www.libpng.org/pub/png/spec/1.2/
:param images: iterator of RGB888 images
:type images: iterator of numpy.ndarray of dimension 3
:param int nb_images: The number of images indicated in the MNG header
:param int fps: The frame rate indicated in the MNG header
:return: An iterator of MNG chunks as bytes
"""
first_image = True
for image in images:
if first_image:
first_image = False
height, width = image.shape[:2]
# MNG signature
yield b"\x8aMNG\r\n\x1a\n"
# MHDR chunk: File header
yield _png_chunk(
"MHDR",
struct.pack(
">IIIIIII",
width,
height,
fps, # ticks
nb_images + 1, # layer count
nb_images, # frame count
nb_images, # play time
1,
),
) # profile: MNG-VLC no alpha: only least significant bit 1
assert image.shape == (height, width, 3)
assert image.dtype == numpy.dtype("uint8")
# IHDR chunk: Image header
depth = 8 # 8 bit per channel
color_type = 2 # 'truecolor' = RGB
interlace = 0 # No
yield _png_chunk(
"IHDR",
struct.pack(">IIBBBBB", width, height, depth, color_type, 0, 0, interlace),
)
# Add filter 'None' before each scanline
prepared_data = b"\x00" + b"\x00".join(
line.tobytes() for line in image
) # TODO optimize that
compressed_data = zlib.compress(prepared_data, 8)
# IDAT chunk: Payload
yield _png_chunk("IDAT", compressed_data)
# IEND chunk: Image footer
yield _png_chunk("IEND", b"")
# MEND chunk: footer
yield _png_chunk("MEND", b"")
