pnmarith
Perform pixel arithmetic on PNM images
TLDR
Add two images
$ pnmarith -add [image1.pnm] [image2.pnm] > [result.pnm]
Subtract images$ pnmarith -subtract [image1.pnm] [image2.pnm] > [result.pnm]
Multiply images$ pnmarith -multiply [image1.pnm] [image2.pnm] > [result.pnm]
Take minimum values$ pnmarith -minimum [image1.pnm] [image2.pnm] > [result.pnm]
SYNOPSIS
pnmarith operation pnmfile1 pnmfile2
DESCRIPTION
pnmarith performs arithmetic operations on two PNM images pixel by pixel. Images must have same dimensions. Useful for compositing, masking, and image comparison.
Superseded by pamarith in modern Netpbm.
PARAMETERS
-add
Add pixel values.-subtract
Subtract pixel values.-multiply
Multiply pixel values.-difference
Absolute difference.-minimum
Minimum of pixels.-maximum
Maximum of pixels.-mean
Average of pixels.
EXAMPLES
$ # Add two images (blend)
pnmarith -add image1.ppm image2.ppm > blended.ppm
# Create difference image
pnmarith -difference frame1.ppm frame2.ppm > diff.ppm
# Multiply (darken with mask)
pnmarith -multiply image.ppm mask.pgm > masked.ppm
# Find minimum
pnmarith -minimum img1.ppm img2.ppm > min.ppm
pnmarith -add image1.ppm image2.ppm > blended.ppm
# Create difference image
pnmarith -difference frame1.ppm frame2.ppm > diff.ppm
# Multiply (darken with mask)
pnmarith -multiply image.ppm mask.pgm > masked.ppm
# Find minimum
pnmarith -minimum img1.ppm img2.ppm > min.ppm
CAVEATS
Images must be same dimensions. Results clamped to valid range. Use pamarith for more options.
HISTORY
pnmarith is part of Netpbm by Jef Poskanzer, providing basic image arithmetic operations.