diff --git a/website/StandardAttributes.rst b/website/StandardAttributes.rst index a1adef062..a15e403d5 100644 --- a/website/StandardAttributes.rst +++ b/website/StandardAttributes.rst @@ -2,6 +2,8 @@ SPDX-License-Identifier: BSD-3-Clause Copyright Contributors to the OpenEXR Project. +.. _Standard Attributes: + Standard Attributes ################### diff --git a/website/python.rst b/website/python.rst new file mode 100644 index 000000000..d19b6b4d1 --- /dev/null +++ b/website/python.rst @@ -0,0 +1,479 @@ +.. + SPDX-License-Identifier: BSD-3-Clause + Copyright Contributors to the OpenEXR Project. + +.. _Python: + +The OpenEXR Python Module +######################### + +.. toctree:: + :caption: Python + +The OpenEXR python module provides basic access to data in EXR image +files. The read and write methods use python dictionaries for header +metadata and numpy arrays for pixel data. + +To install the OpenEXR module: + +.. code-block:: + + % pip install OpenEXR + +The module is specifically designed for maximum simplicity and ease of +use, not for high performance. If your application deals with +especially large data files, is particular about memory management, or +needs low level operations like reading specific scanlines or tiles, +this may not be the module for you. But if your application is +comfortable reading entire files into memory and can deal with pixel +data in numpy arrays, the OpenEXR module is a suitable option. + +A Note about Backwards Compatibility +==================================== + +The v3.3 release of the OpenEXR module provides an entirely new API in +the form of the ``OpenEXR.File`` object. This API is full-featured and +fully supported going forward. + +The original implementation of the OpenEXR python bindings prior to +the v3.3 release used the ``InputFile`` and ``OutputFile`` +objects. This API is limited in scope, and is now deprecated. It is +still distributed as is for backwards compatibility, but usage is +discouraged. + +Example Images +============== + +See :ref:`Test Images` for example images to experiment with. + +Reading and Writing in a Nutshell +================================= + +Generate random RGB data and write it to an EXR file: + +.. code-block:: + + import OpenEXR + + height, width = (1080, 1920) + RGB = np.random.rand(height, width, 3).astype('float32') + channels = { "RGB" : RGB } + header = { "compression" : OpenEXR.ZIP_COMPRESSION, + "type" : OpenEXR.scanlineimage } + + with OpenEXR.File(header, channels) as outfile: + outfile.write("image.exr") + +This creates a scanline image of size 10x20 pixels with R, G, and B +channels of type float, initialized to random values, and writes it to +the file ``test.exr``, compressed with ZIP compression. + +Correspondingly, to read an image and print its pixel data: + +.. code-block:: + + import OpenEXR + + with OpenEXR.File("image.exr") as infile: + + header = infile.header() + print(f"type={header['type']}") + print(f"compression={header['compression']}") + + RGB = infile.channels()["RGB"].pixels + height, width = RGB.shape[0:2] + for y in range(height): + for x in range(width): + pixel = (RGB[y, x, 0], RGB[y, x, 1], RGB[y, x, 2]) + print(f"pixel[{y}][{x}]={pixel}") + +Reading EXR Files with OpenEXR.File +=================================== + +The basic construct of the OpenEXR module is the ``File`` object. +Construct a ``File`` object with a filename as the parameter and it +reads the image data into the object: + +.. code-block:: + + >>> exrfile = OpenEXR.File("StillLife.exr") + +OpenEXR.Part +------------ + +An EXR file consists of a list called ``parts`` of one or more parts, +which the OpenEXR python module represents with the ``Part`` object. A +part consists of a dictionary called ``header`` that holds the +attribute metadata, and a dictionary called ``channels`` that hold the +pixel data. + +.. code-block:: + + >>> exrfile = OpenEXR.File("StillLife.exr") + >>> part = exrfile.parts[0] + >>> part.height() + 846 + >>> part.width() + 1240 + + >>> for name,value in part.header.items(): + ... print(name, value) + ... + capDate 2002:06:23 21:30:10 + channels [Channel("A", xSampling=1, ySampling=1), Channel("B", xSampling=1, ySampling=1), Channel("G", xSampling=1, ySampling=1), Channel("R", xSampling=1, ySampling=1)] + compression Compression.PIZ_COMPRESSION + dataWindow (array([0, 0], dtype=int32), array([1239, 845], dtype=int32)) + displayWindow (array([0, 0], dtype=int32), array([1239, 845], dtype=int32)) + lineOrder LineOrder.INCREASING_Y + owner Copyright 2002 Industrial Light & Magic + pixelAspectRatio 1.0 + preview PreviewImage(100, 68) + screenWindowCenter [0. 0.] + screenWindowWidth 0.44999998807907104 + type Storage.scanlineimage + utcOffset 25200.0 + + >>> for name,channel in part.channels.items(): + ... print(name, channel, channel.pixels.shape, channel.pixels.dtype) + ... + RGBA Channel("RGBA", xSampling=1, ySampling=1) (846, 1240, 4) float16 + +Since many common EXR files have only a single part, for convenience, +the ``File`` object has ``header()`` and ``channels()`` methods that + +Header Metadata +--------------- + +The ``File`` object's ``header()`` method returns a dictionary holding +the file's metadata. The dictionary key is the metadata attribute +name, and the dictionary value is an object holding the attribute value. + +An EXR file header can store metadata attributes with any name, but see +:ref:`Standard Attributes` for a complete description of the standard +attributes in an EXR file, both required and optional, which have +strictly enforced types. + +Supported types of metadata are: + +* string +* list of strings +* integer +* float +* list of floats +* V2i, V2f, V2d, V3i, V3f, V3d - 2D and 3D vectors, represented as 2x1 + or 3x1 numpy arrays with a ``dtype`` of ``int32``, ``float32``, or ``float64``. +* M33f, M33d, M44f, M44d - 3x3 or 4x4 matrices, represented as 3x3 or + 4x4 numpy arrays with a ``dtype`` of ``float32`` or ``float64``. +* Box2i, Box2f - bounding boxes, represented as tuples of numpy arrays (``min`` and + ``max``) with a ``dtype`` of ``int32`` or ``float32``. + +The OpenEXR module has enumerated types for certain attributes: + +.. raw:: html + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
attribute name type values
+

type

+ 		OpenEXR.Storage +
    +
  • OpenEXR.scanlineimage +
  • OpenEXR.tiledimage +
  • OpenEXR.deepscanline +
  • OpenEXR.deeptile +
  • OpenEXR.NUM_STORAGETYPES +
+
+

lineOrder

+ 		OpenEXR.LineOrder +
    +
  • OpenEXR.INCREASING_Y +
  • OpenEXR.DECREASING_Y +
  • OpenEXR.RANDOM_Y +
  • OpenEXR.NUM_LINE_ORDERS +
+
+

compression

+ 		OpenEXR.Compression +
    +
  • OpenEXR.NO_COMPRESSION +
  • OpenEXR.RLE_COMPRESSION +
  • OpenEXR.ZIPS_COMPRESSION +
  • OpenEXR.ZIP_COMPRESSION +
  • OpenEXR.PIZ_COMPRESSION +
  • OpenEXR.PXR24_COMPRESSION +
  • OpenEXR.B44_COMPRESSION +
  • OpenEXR.B44A_COMPRESSION +
  • OpenEXR.DWAA_COMPRESSION +
  • OpenEXR.DWAB_COMPRESSION +
  • OpenEXR.NUM_COMPRESSION_METHODS +
+
+ + + +The ``dataWindow`` Attribute and Image Size +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The ``dataWindow`` attribute is especially important. Its size matches +the shape of the channel pixel arrays. The ``min`` of the +``dataWindow`` attribute specifies the row/column coordinate of the +pixel at the origin of the image. However, the numpy arrays holding +the pixel data are *not* offset by this value. + +.. code-block:: + + >>> min,max = exrfile.header()["dataWindow"] + >>> height = max[1] - min[1] + 1 + >>> width = max[0] - min[0] + 1 + >>> height,width + (846, 1240) + +OpenEXR.Channel +--------------- + +The ``channels()`` method of the ``File`` object returns a dictionary +holding pixel data. The key is the channel name and the value is a +``Channel`` object. + +The ``Channel`` object has a ``pixels`` field that is a 2D numpy array +holding the pixel data. Supported types are ``uint32``, ``float16``, +and ``float32``. + +For parts that contain RGB data, where the file contains separate +``R``, ``G``, ``B``, and optionally ``A`` channels, the channels +dictionary holds a single channel named ``RGB`` and with a numpy array +of shape ``(height, width, 3)``, or ``RGBA`` and a numpy array of +shape ``(height, width, 4)`` if there is alpha. + +All channels within a part have the same width and height, and thus +the same pixel array shape. + +For single-part files, ``channels()`` returns the image channels for the +file. For multi-part files, ``channels()`` takes a part number as +argument and returns the channels for that part: + +.. code-block:: + + >>> for p in range(len(exrfile.parts)): + ... for name,channel in exrfile.channels(p).items(): + ... print(name, channel.pixels.shape, channel.pixels.dtype) + ... + RGBA (846, 1240, 4) float16 + + +The channel object also has ``xSampling``, ``ySampling``, and +``pLinear`` fields that hold the channel’s subsampling values and +plinear setting used for DWA compression. The default sampling values +are 1 and are only used for luminance subsampling. + +Pixel Arrays +~~~~~~~~~~~~ + +The first dimension of a channel's ``pixels`` array is the image +height. The second dimension is the image width. All channels of a +part must have the same width and height. It's an error to create or +write a File object with channels of different shapes. The ``Part`` +object has ``height()`` and ``width()`` methods that return the image +dimension. You can, of course, query the dimension of a channel via +the pixel array itself. + +.. code-block:: + + >>> part = exrfile.parts[0] + >>> dw = part.header['dataWindow'] + >>> height = part.height() + >>> width = part.width() + >>> for name,channel in part.channels.items(): + ... print(name, channel.pixels.shape, height, width, dw) + ... + (846, 1240, 4) 846 1240 (array([0, 0], dtype=int32), array([1239, 845], dtype=int32)) + +The ``File`` object allocates space for the pixel arrays upon +read. There is no mechanism to provide memory addresses for the pixel +arrays. + +Pixel Array Data Layout +~~~~~~~~~~~~~~~~~~~~~~~ + +Although the OpenEXR file format supports channels of arbitrary name +and number of type ``uint32``, ``float16``, and ``float32``, most +programs working with OpenEXR files expect this data to represent +pixels, so it's more convenient to group ``R``, ``G``, ``B``, and +``A`` channels together. By default, the ``File`` object does this and +returns a channel with name ``RGB`` and a numpy array of shape +``(height, width, 3)``, or ``RGBA`` and a numpy array of shape +``(height, width, 4)`` if there is alpha. + +The ``File()`` object constructor takes an optional +``separate_channels`` argument, ``False`` by default, but if ``True``, +it skips the channel grouping and returns each channel as a separate +2D numpy array. + +Tiled Images +------------ + +The ``File`` object reads tiled EXR images into pixel arrays just the +same as scanline images. + +Although the EXR format supports multiple tile levels, currently, the +API provides no access to these levels. + +Deep Images +----------- + +Deep EXR files store an arbitrary number of data values per pixel. For +deep parts, the ``Channel`` object's ``pixels`` array has a ``dtype`` +of ``object``, which is in turn a 1D numpy array holding the deep samples +for that pixel. Supported types for the deep sample array are +``uint32``, ``float16``, and ``float32``. + +If the deep sample array object for a given pixel is ``None``, there +are no samples for that pixel. + +.. code-block:: + + RGB = infile.channels()["RGB"].pixels + height, width = R.shape + for y in range(height): + for x in range(width): + if R[y,x].dtype == None: + print(f"No samples for pixel {y},{x}") + else: + for i in range(RGB[y,x].shape(0)): + print(f"pixel {y},{x} sample[{i}]: {RGB[y,x]}") + +All channel within a given deep part must have the same number of +samples, so the deep sample arrays for all channels have the same size +and shape. + +Writing EXR Files with OpenEXR.File +=================================== + +To write an EXR file, construct a ``File`` object and call the +``write()`` method. + +For single-part files, the ``File`` object constructor takes a +dictionary for the header and a dictionary for the channels. + +Construct the channels dict with values that are either numpy arrays +or ``Channel`` objects if you need to specify the ``xSampling``, +``ySampling``, or ``pLinear`` values. + +The channel pixel arrays must have a ``dtype`` of ``uint32``, +``float16``, or ``float32``. + +All channel pixel arrays within a given part must have the same +dimenions. The ``write`` method will throw an exception if they are +not. + +.. code-block:: + + height, width = (20, 10) + RGB = np.random.rand(height, width, 3).astype('f') + channels = { "RGB" : RGB } + header = { "compression" : OpenEXR.ZIP_COMPRESSION, + "type" : OpenEXR.scanlineimage } + + with OpenEXR.File(header, channels) as outfile: + outfile.write("test.exr") + +Writing Multi-Part EXR Files +---------------------------- + +For multi-part images, pass the ``File`` constructor a list of +``Part`` objects, each of which holds the header and channels dicts. + +.. code-block:: + + height, width = (20, 10) + Z0 = np.zeros((height, width), dtype='float32') + Z1 = np.ones((height, width), dtype='ffloat32') + + P0 = OpenEXR.Part({}, {"Z" : Z0 }) + P1 = OpenEXR.Part({}, {"Z" : Z1 }) + + f = OpenEXR.File([P0, P1]) + f.write("readme_2part.exr") + + with OpenEXR.File("multipart.exr") as o: + assert o.parts[0].name() == "Part0" + assert o.parts[0].width() == 10 + assert o.parts[0].height() == 20 + assert o.parts[1].name() == "Part1" + assert o.parts[1].width() == 10 + assert o.parts[1].height() == 20 + +Writing Tiled EXR Files +----------------------- + +To write a tiled image, set the ``type`` header attribute to +``OpenEXR.tiledimage`` and the ``tiles`` header attribute to an object +of type ``OpenEXR.TileDescription`` with the appropriate settings. + +.. code-block:: + + height, width = (20, 10) + + Z = np.zeros((height, width), dtype='f') + channels = { "Z" : Z } + header = { "type" : OpenEXR.tiledimage, + "tiles" : OpenEXR.TileDescription(), + "compression" : OpenEXR.ZIPSCOMPRESSION } + + with OpenEXR.File(channels, header) as exrfile: + exrfile.write("tiled.exr") + + +Writing Deep EXR Files +---------------------- + +For deep images, the channel pixel arrays must have a ``dtype`` of +``object``, or ``None`` for pixels with no samples. The object must +be a numpy array with a ``dtype`` of ``uint32``, ``float16``, or +``float32``. + +.. code-block:: + + height, width = (20, 10) + + Z = np.empty((height, width), dtype=object) + for y in range(height): + for x in range(width): + Z[y, x] = np.array([y*width+x], dtype='float32') + + channels = { "Z" : Z } + header = { "compression" : OpenEXR.ZIPS_COMPRESSION, + "type" : OpenEXR.deepscanline } + with OpenEXR.File(header, channels) as outfile: + outfile.write("deep.exr") + +All deep pixel arrays within a given part must have the same number of +samples, so the pixel arrays must have the same size and shape. The +``write`` method will throw an exception if they are not. + diff --git a/website/test_images/index.rst b/website/test_images/index.rst index 7c1ec5da4..32dc7c00f 100644 --- a/website/test_images/index.rst +++ b/website/test_images/index.rst @@ -1,6 +1,8 @@ Test Images ########### +.. _Test Images: + .. toctree:: :caption: Test Images :maxdepth: 2 diff --git a/website/toc_redirect.rst b/website/toc_redirect.rst index ba3c51ac7..1a70ae2d6 100644 --- a/website/toc_redirect.rst +++ b/website/toc_redirect.rst @@ -17,6 +17,11 @@ API +.. toctree:: + :hidden: + + python + .. toctree:: :hidden: