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cookbook.md

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Cookbook

Some example usage

Use LINK to import

]LINK.Create pnm /Users/ldbeth/Public/Projects/pnmaster/APL_code

Image formats

Prepare an image NetPBM format

PNG

pngtopnm input.png > out.ppm

The program automatically decides whether it outputs PPM or PGM, in case the PNG image only uses gray scale. The NetPBM programs always write output to standard ourput.

Use pgmtoppm to promote an PGM image to PPM, or in the APL,

(⊢⍴⍨3,⍴)image

readpnm

    input←pnm.readpnm 'input.pgm'

writepnm

    ⌈/,bit
1
    bit pnm.writepnm 'P4' 'output.pbm' ⍝ PBM file.
    ⌈/,grey
255
    grey pnm.writepnm 'P5' 'output.pgm' ⍝ PGM file.
    ≢color
3
    ⌈/,color
255
    color pnm.writepnm 'P6' 'output.ppm' ⍝ PPM file.

Blue noise pattern and dither

Generate a blue noise pattern of specified radius for dithering:

      ⍴pnm.Image.Bluenoise.mkda 13
26 26
      ⍴pnm.Image.Bluenoise.MASK64 ⍝ Precomputed pattern
64 64

Convert the PGM to PBM using dithering:

pbm←pnm.Image.(Bluenoise.MASK64⍤Dither.dither) pgm

Curvature filter

out←pnm.(Pgm.quantize∘Image.curva) in

Knuth's dot diffusion

out←pnm.Image.(Bluenoise.MASK32∘Dither.diffuse) in

CIELAB Steganography

lab←pnm.Ppm.cielab pnm.readpnm 'b.ppm'
bin←pnm.readpnm 'o.pbm' ⍝ binary image to hide
pnm.Image.Stega.histo lab ⍝ Find the direction that occurs less
t←pnm.Image.Stega.direc 95
out←lab (t pnm.Image.Stega.gdb 3) bin
ppm←pnm.Ppm.delab out
ppm pnm.writepnm 'P6' 'o.ppm'
decode←pnm.Ppm.cielab pnm.readpnm 'o.ppm'
r←95 pnm.Image.Stega.decode decode
r pnm.writepnm 'P4' 'dec95.pbm'