This simple module provides Python bindings for the fast PNG encoder, fpnge.

Installation

This module has only been tested with Python3. Distutils is required (apt install python3-distutils under Debian based distros should grab it).

fpnge currently only runs on x86 processors, and requires SSE4.1 support at minimum. Note: there is no dynamic CPU detection implemented, so this module should be installed/compiled on the machine it is going to run on.

This module can then be installed by running python3 setup.py install in the folder with the code.

Example Usage

Exporting a PIL.Image to a PNG file.

from PIL import Image
import fpnge

with Image.open('input.png') as im:
	png = fpnge.fromPIL(im)
	with open('output.png', 'wb') as f:
		f.write(png)

API

Note: fpnge does not support indexed color or bit depths below 8 bits/pixel.

fpnge.fromPIL(image)

Converts a PIL image specified in image to a PNG, returning it as a bytes object. If the image uses a palette, it will be converted to RGBA before saving.

fpnge.frombytes(bytes, width, height, channels, bits_per_channel [, stride])

Converts a raw image specified as a bytes object in bytes to a PNG, returning it as a bytes object.

The pixel dimensions of the supplied image must be specified in width and height, with stride being the number of bytes per row (if unspecified, assumes stride = width * channels * bits_per_channel/8). bits_per_channel signifies the bit depth for each colour channel. Only 8 and 16 bits per channel are supported. Note that if 16 bits per channel is selected, samples must be big-endian. channels refers to the number of colour channels the image has, with the following assumption:

• 1 channel: this is a greyscale image
• 2 channels: this is a greyscale + alpha image. Channels are interleaved with greyscale being first, followed by alpha.
• 3 channels: RGB colour. Channel interleaving order is: red, green, blue.
• 4 channels: RGBA colour. Channel interleaving order is: red, green, blue, alpha.

No other values are allowed for channels

fpnge.fromNP(ndarray)

Converts a raw image stored in a 3-dimensional NumPy ndarray to a PNG, returning it as a bytes object.

The dimensions must be height, width and colour channels (see frombytes function above for how the channel count is interpreted and channel components are ordered).
The element type should be a uint8 or '>u2'.

Note: This differs from the Pillow definition of shape which is (width, height, channels)

fpnge.fromview(view [, width] [, height] [, channels] [, bits_per_channel] [, stride])

The memoryview version of frombytes, where view is a C-contiguous memoryview.

If other arguments are not supplied, assumes view is a 3-dimensional structure (width x height x channels) and derives the values from there.

See Also

Python bindings for the other speed-optimized PNG writer, fpng.

License

This module is Public Domain or CC0 (or equivalent) if PD isn’t recognised.

fpnge itself is licensed under the Apache License 2.0