PeachPDF
PeachPDF
ImageCompression Enum
How an opaque, lossless raster source is embedded, set via ImageCompression. PNG, BMP, and GIF always qualify (none of the three has a lossy encoding mode at all). WebP, AVIF, and TIFF each support both a lossy and a lossless encoding mode, so a source in one of those formats only qualifies when it was actually encoded losslessly - a lossy-encoded WebP/AVIF/TIFF is unaffected by this setting in every mode and stays on the same JPEG-re-encode path it always used.
public enum ImageCompression
Fields
Auto 0
Default. A PNG eligible for byte-for-byte /FlateDecode pass-through - not interlaced,
and either fully opaque or carrying only a tRNS chroma-key transparency PDF’s own
color-key /Mask mechanism can represent (a real per-pixel alpha channel still needs the
existing decode+/SMask path) - is always embedded that way, regardless of
DownscaleImages - pass-through can’t be resized, the same as a
CMYK JPEG is always embedded at natural size. A lossless source (PNG/BMP/GIF always, or a
losslessly-encoded WebP/AVIF/TIFF) that isn’t pass-through-eligible at its own natural size (an
interlaced PNG, or a format with no pass-through mechanism at all) still never gets re-encoded
as lossy JPEG - it falls back to the existing decode-and-/FlateDecode path instead. One
being downscaled (its on-page display size is smaller
than its natural size) keeps the existing downscale-to-JPEG-at-DownscaleQuality
behavior unchanged, since that’s an intentional, separate size/quality trade-off - except a
tRNS-transparent source, which stays pass-through-embedded (and so natural-size)
regardless of downscaling too, since JPEG can’t represent that transparency at all.
Lossless 1
Same as Auto, but a downscaled opaque lossless source also never gets re-encoded as
lossy JPEG - it’s decoded, resampled, and re-/FlateDecode-encoded instead of
JPEG-compressed at DownscaleQuality. Larger downscaled output,
always pixel-exact regardless of size. A tRNS-transparent PNG being downscaled is
unaffected by this distinction either way - it already forfeits pass-through and falls into
that same decode+resize path under both Auto and this value, since its real,
decoded alpha survives the resize correctly regardless of which of these two modes triggered it.
Lossy 2
Always re-encode an opaque PNG/BMP/GIF as JPEG, even one that would otherwise be pass-through-
eligible - the behavior every version of PeachPDF used before this option existed. An explicit
opt-in for anyone who wants the smallest files even for diagram/line-art content and accepts
the fidelity loss. Doesn’t apply to a tRNS-transparent PNG: JPEG has no way to represent
that transparency at all, so forcing it through the lossy path would silently make the
transparent color solid instead of merely losing some fidelity - the same source is still
embedded via pass-through under this value too, exactly like a real per-pixel-alpha PNG is
already unaffected by every value of this setting.