PeachImage
PeachImage.Formats.Png.PngAlphaSplitInfo
PngAlphaSplitInfo.AlphaData Property
A complete, independent zlib (RFC 1950) stream of single-channel (DeviceGray) alpha samples,
<b>PNG-filtered exactly like a PNG <c>IDAT</c> stream</b> — every row is prefixed with a filter-type
byte (always 0/None here) followed by Width sample bytes, the same row shape a real PNG
file’s own IDAT uses. This is deliberate, not raw flat pixel bytes: it lets a caller embed this
stream as a PDF /FlateDecode/SMask with /DecodeParms << /Predictor 15 /Colors 1
/BitsPerComponent 8 /Columns >> — PDF’s own “PNG prediction” mechanism,
which a compliant PDF reader decodes identically to a real PNG row filter — the same technique already
applies to IdatData itself (which keeps its original filter bytes
verbatim), so this keeps both halves of a split image consistent with how PNG-sourced PDF image data
is always framed.
public byte[] AlphaData { get; init; }