PyPNG

Warnings

• breaking The `lenient` flag has been removed. PNG chunk checksum errors are now treated as warnings instead of exceptions and can be managed using Python's standard `warnings` module.
  Fix: Remove the `lenient` flag from your `Reader` initialization. Handle checksum warnings via Python's `warnings` module if needed.
• breaking The `interlace` keyword argument has been removed from the `Writer` class, and interlaced output is no longer supported.
  Fix: Remove the `interlace` argument from `png.Writer` calls. If interlaced output is strictly required, an older version of `pypng` or an alternative library must be used.
• breaking Passing an empty file to PyPNG now raises a built-in `EOFError` instead of `png.FormatError`. This change helps distinguish empty file issues from genuine format errors.
  Fix: Update exception handling to catch `EOFError` for empty file scenarios, while still catching `png.FormatError` for other invalid PNG format issues.
• gotcha Files for reading or writing PNGs must always be opened in binary mode (e.g., `'wb'` for writing, `'rb'` for reading) to prevent data corruption or unexpected errors.
  Fix: Ensure file opening statements explicitly include the binary mode flag (e.g., `with open('image.png', 'wb') as f:`).
• gotcha Incorrect bit depth specification or pixel data formatting can lead to corrupted images. Pixel data must match the `Writer` configuration (e.g., grayscale, RGB, RGBA) and the declared bit depth.
  Fix: Carefully align the pixel data structure and values with the `bitdepth`, `greyscale`, and `alpha` parameters when initializing `png.Writer` or using `png.from_array`'s mode argument. For example, 'L;16' for 16-bit grayscale.
• gotcha When calculating image dimensions, especially for `width` from row data (e.g., `len(row) / channels_per_pixel`), ensure you use integer division (`//`) instead of float division (`/`). Using float division where an integer is expected can lead to `TypeError`.
  Fix: Replace `/` with `//` for calculations that are expected to result in an integer, such as `width = len(row) // 3` for an RGB image.

Install

• pip install pypng Install with pip

Imports

• png

  import png

  The PyPI package name is `pypng`, but the module is imported as `png`.

Quickstart

This quickstart demonstrates how to create a simple grayscale PNG image from a Python list of lists representing pixel data. It uses the `png.from_array` function for convenience and saves the image to a file.

import png
import os

# Create a simple 2x2 grayscale image (Luminance) with a bit depth of 8
rows = [
    [255, 0], # White, Black
    [0, 255]  # Black, White
]

# Create an image from a 2D array and save it
image_file_path = 'simple_image.png'
png.from_array(rows, 'L').save(image_file_path)

print(f"Image saved to {image_file_path}")

# Clean up the created file
# os.remove(image_file_path)