Creating imageio plugins
========================
.. automodule:: imageio.plugins
Example / template plugin
-------------------------
.. code-block:: python
:linenos:
# -*- coding: utf-8 -*-
# imageio is distributed under the terms of the (new) BSD License.
""" Example plugin. You can use this as a template for your own plugin.
"""
from __future__ import absolute_import, print_function, division
import numpy as np
from .. import formats
from ..core import Format
class DummyFormat(Format):
""" The dummy format is an example format that does nothing.
It will never indicate that it can read or write a file. When
explicitly asked to read, it will simply read the bytes. When
explicitly asked to write, it will raise an error.
This documentation is shown when the user does ``help('thisformat')``.
Parameters for reading
----------------------
Specify arguments in numpy doc style here.
Parameters for saving
---------------------
Specify arguments in numpy doc style here.
"""
def _can_read(self, request):
# This method is called when the format manager is searching
# for a format to read a certain image. Return True if this format
# can do it.
#
# The format manager is aware of the extensions and the modes
# that each format can handle. It will first ask all formats
# that *seem* to be able to read it whether they can. If none
# can, it will ask the remaining formats if they can: the
# extension might be missing, and this allows formats to provide
# functionality for certain extensions, while giving preference
# to other plugins.
#
# If a format says it can, it should live up to it. The format
# would ideally check the request.firstbytes and look for a
# header of some kind.
#
# The request object has:
# request.filename: a representation of the source (only for reporting)
# request.firstbytes: the first 256 bytes of the file.
# request.mode[0]: read or write mode
# request.mode[1]: what kind of data the user expects: one of 'iIvV?'
if request.mode[1] in (self.modes + "?"):
if request.extension in self.extensions:
return True
def _can_write(self, request):
# This method is called when the format manager is searching
# for a format to write a certain image. It will first ask all
# formats that *seem* to be able to write it whether they can.
# If none can, it will ask the remaining formats if they can.
#
# Return True if the format can do it.
# In most cases, this code does suffice:
if request.mode[1] in (self.modes + "?"):
if request.extension in self.extensions:
return True
# -- reader
class Reader(Format.Reader):
def _open(self, some_option=False, length=1):
# Specify kwargs here. Optionally, the user-specified kwargs
# can also be accessed via the request.kwargs object.
#
# The request object provides two ways to get access to the
# data. Use just one:
# - Use request.get_file() for a file object (preferred)
# - Use request.get_local_filename() for a file on the system
self._fp = self.request.get_file()
self._length = length # passed as an arg in this case for testing
self._data = None
def _close(self):
# Close the reader.
# Note that the request object will close self._fp
pass
def _get_length(self):
# Return the number of images. Can be np.inf
return self._length
def _get_data(self, index):
# Return the data and meta data for the given index
if index >= self._length:
raise IndexError("Image index %i > %i" % (index, self._length))
# Read all bytes
if self._data is None:
self._data = self._fp.read()
# Put in a numpy array
im = np.frombuffer(self._data, "uint8")
im.shape = len(im), 1
# Return array and dummy meta data
return im, {}
def _get_meta_data(self, index):
# Get the meta data for the given index. If index is None, it
# should return the global meta data.
return {} # This format does not support meta data
# -- writer
class Writer(Format.Writer):
def _open(self, flags=0):
# Specify kwargs here. Optionally, the user-specified kwargs
# can also be accessed via the request.kwargs object.
#
# The request object provides two ways to write the data.
# Use just one:
# - Use request.get_file() for a file object (preferred)
# - Use request.get_local_filename() for a file on the system
self._fp = self.request.get_file()
def _close(self):
# Close the reader.
# Note that the request object will close self._fp
pass
def _append_data(self, im, meta):
# Process the given data and meta data.
raise RuntimeError("The dummy format cannot write image data.")
def set_meta_data(self, meta):
# Process the given meta data (global for all images)
# It is not mandatory to support this.
raise RuntimeError("The dummy format cannot write meta data.")
# Register. You register an *instance* of a Format class. Here specify:
format = DummyFormat(
"dummy", # short name
"An example format that does nothing.", # one line descr.
".foobar .nonexistentext", # list of extensions
"iI", # modes, characters in iIvV
)
formats.add_format(format)
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