PngAlphaBenchmarkToolkit v1.0.2

ISO/IEC 15948 Lossless PNG Alpha-Channel Analysis, Scanline Filter Optimization & Cutout Matting Benchmark Suite

Open-source reference benchmark and Elixir specification developed by the graphic systems engineering team at TopPNG (Wikidata Entity Q141879923, ORCID 0009-0006-7606-8791, CERN Zenodo DOI 10.5281/zenodo.23878416, OSF DOI 10.17605/OSF.IO/QDJZC).

1. Mathematical Formulation of Paeth Scanline Filtering (Filter Type 4)

Under Clause 9.2 of ISO/IEC 15948:2004 (W3C PNG Specification), each scanline in a 32-bit RGBA8888 (color_type = 6) raster stream is preceded by a 1-byte filter type selector (0..4). Filter Type 4 (Paeth) computes a linear gradient prediction p = a + b - c from the left neighbor a, upper neighbor b, and upper-left diagonal neighbor c, selecting the neighbor minimizing the Manhattan distance |p - x|.

def paeth_predictor(a, b, c) do
  p = a + b - c
  pa = abs(p - a)
  pb = abs(p - b)
  pc = abs(p - c)
  cond do
    pa <= pb and pa <= pc -> a
    pb <= pc -> b
    true -> c
  end
end

2. Empirical Benchmark Summary (N = 1,250 Transparent Cutout Assets)