PaperForge.Images.PNG (PaperForge v0.2.0)

Reads PNG metadata and image data for embedding in PDF image XObjects.

PNG image data is stored as zlib-compressed scanlines in IDAT chunks. PDF can consume non-alpha image data directly through /FlateDecode when paired with PNG predictor decode parameters.

For alpha PNGs, this module decodes PNG scanline filters, separates color bytes from alpha bytes, and returns a separate soft-mask stream.

This module supports non-interlaced 8-bit grayscale, RGB, grayscale with alpha, and RGBA PNG images. Adam7 interlacing and palette PNGs are intentionally unsupported.

Summary

Types

color_space()

error_reason()

metadata()

Functions

parse(arg1)

Reads PNG metadata and concatenated compressed IDAT data.

parse!(data)

Reads PNG metadata and raises when the binary is invalid or unsupported.

png?(arg1)

Returns whether a binary begins with the PNG signature.

Types

color_space()

@type color_space() :: :device_gray | :device_rgb

error_reason()

@type error_reason() ::
  :invalid_png
  | :missing_ihdr
  | :missing_idat
  | :truncated_chunk
  | :invalid_ihdr
  | :unsupported_compression
  | :unsupported_filter
  | :unsupported_interlace
  | :invalid_image_data
  | {:unsupported_color_type, non_neg_integer()}
  | {:unsupported_bit_depth, non_neg_integer(), non_neg_integer()}

metadata()

@type metadata() :: %{
  width: pos_integer(),
  height: pos_integer(),
  color_type: non_neg_integer(),
  bits_per_component: pos_integer(),
  components: pos_integer(),
  color_space: color_space(),
  compressed_data: binary(),
  smask_compressed_data: binary() | nil
}

Functions

parse(arg1)

@spec parse(binary()) :: {:ok, metadata()} | {:error, error_reason()}

Reads PNG metadata and concatenated compressed IDAT data.

parse!(data)

@spec parse!(binary()) :: metadata()

Reads PNG metadata and raises when the binary is invalid or unsupported.

png?(arg1)

@spec png?(binary()) :: boolean()

Returns whether a binary begins with the PNG signature.