Predictors

TIFF + PNG predictors for FlateDecode (ISO 32000-1 §7.4.4.4).

Predictors are a post-decode pass that undoes a per-row delta encoding the producer applied before compression — they help DEFLATE compress smoothly varying data (like a grayscale gradient) much better. Almost every PDF 1.5+ xref stream uses predictor 12 (PNG Up).

Predictor codes: 1 None (passthrough) 2 TIFF Predictor 2 10 PNG None (filter byte = 0) 11 PNG Sub (filter byte = 1) 12 PNG Up (filter byte = 2) 13 PNG Average (filter byte = 3) 14 PNG Paeth (filter byte = 4) 15 PNG Optimum (per-row filter byte selects 0..4)