LOWP(1)

NAME

lowp - 3D low-pass filter across three sequential pix files

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SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
AUTHOR
COPYRIGHT
BUG REPORTS

SYNOPSIS

lowp file1.pix file2.pix file3.pix [width] > out.pix

DESCRIPTION

lowp reads three sequential pix(5) image files of identical dimensions and applies a 3D low-pass convolution filter, writing a single smoothed pix(5) image to standard output.

The three inputs are treated as consecutive frames in a sequence. A 3x3x3 spatial-temporal kernel is applied: each output pixel is the weighted average of the corresponding pixel and its eight neighbors in the middle frame (file2.pix), together with the same neighborhoods in the preceding (file1.pix) and succeeding (file3.pix) frames. The middle frame is weighted most heavily and the kernel weights sum to 84.

Images are assumed to be square. The dimension defaults to 512x512 pixels; if the images are a different size, supply the optional width argument to set the number of pixels per scanline (and the number of scanlines). The border pixels (first and last scanline, and the first and last pixels of every scanline) are not filtered and are written as black.

lowp refuses to write to a terminal, so its output must be redirected to a file or piped to another program.

OPTIONS

file1.pix file2.pix file3.pix: The three input pix(5) files, given as a sequence of frames. The middle file is the frame that is smoothed.
width: Width and height, in pixels, of the (square) input images. Defaults to 512.

EXAMPLES

Example 1. Temporally smoothing a rendered animation frame

rt -s 1024 -o frame1.pix model.g region &&
rt -s 1024 -o frame2.pix model.g region &&
rt -s 1024 -o frame3.pix model.g region
lowp frame1.pix frame2.pix frame3.pix 1024 > smoothed.pix
pix-png -s 1024 smoothed.pix > smoothed.png

Renders three 1024x1024 frames with rt(1), blends them into a smoothed middle frame to reduce per-frame noise and aliasing, and converts the result to PNG with pix-png(1).