UMOD(1)

NAME

umod - apply arithmetic operations to a stream of 16-bit unsigned short integers

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SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
AUTHOR
COPYRIGHT
BUG REPORTS

SYNOPSIS

umod [-a add] [-s sub] [-m mult] [-d div] [-A] [-e exp] [-r root] [file.s] > output.s

umod reads a stream of 16-bit unsigned short integers, applies a chain of arithmetic operations to each value, and writes the modified stream to standard output. Any number of add, subtract, multiply, divide, exponentiation, and absolute-value operations may be given; they are applied in the exact order they appear on the command line.

To avoid recomputing the operations for every sample, umod precomputes a lookup table covering all 65536 possible input values. Results that exceed the representable range are clipped to 65535 (high) or 0 (low), and the total number of clipped values is reported to standard error when processing finishes.

If file.s is given it is read as input; otherwise umod reads from standard input. The companion tools smod(1) and imod(1) perform the same operations on signed short integer streams, and dmod(1) operates on double-precision floating point streams.

OPTIONS

-a add: Add add to each value.
-s sub: Subtract sub from each value.
-m mult: Multiply each value by mult.
-d div: Divide each value by div. A divisor of zero is an error.
-A: Replace each value with its absolute value. Since the input is unsigned this only has an effect when a prior operation (such as subtraction) produced a negative intermediate result.
-e exp: Raise each value to the power exp.
-r root: Take the root root of each value (equivalent to raising to the power 1/root). A root of zero is an error.

EXAMPLES

Example 1. Bias and scale a sample stream

umod -a 100 -m 3 data.s > scaled.s

For each value, 100 is added first and the result is then multiplied by 3, writing the modified unsigned shorts to scaled.s. Because operations apply in command-line order, swapping -a and -m would yield a different result.

Example 2. Convert a pixel image to a stream and stretch its contrast

pix-bw scene.pix | bw-d | d-u | umod -s 8000 -m 2 > stretched.s

The intensity of a pix(5) image is reduced to a single channel, converted to an unsigned short stream, then darkened by subtracting an offset and brightened by doubling, demonstrating umod used as a stage in a pipeline.