codec / predictor · 2D / lossless

average

A simple guess from the values above and to the left.

average predicts each sample from the average of its west and north neighbours. It is useful when a surface changes in both directions without strong edges. The calculation uses an overflow-safe integer form, and missing neighbours along the top and left borders count as zero.

ctid

0x72D706

header

uint32 · row width in samples
+ uint32 · plane count, when above one

widths

8 · 16 · 32 · 64-bit integers

decode

floor((W + N) / 2) per sample, in order