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vsynth.1Vi

NAME

vsynth - synthesize an image

SYNOPSIS

vsynth -pattern pattern [-option ...] [outfile]

DESCRIPTION

vsynth creates a one-band image with a specified size, pixel representation, and pattern of pixel values.

The program knows how to create several different types of patterns. These are described below under PATTERNS.

COMMAND LINE OPTIONS

vsynth accepts the following options in addition to those described below under PATTERNS.

-help

Prints a message describing options.

-out outfile

Specifies where the synthesized image is to be written as a Vista data file.

-pattern pattern

Specifies, with one of the keywords listed below, the type of pattern to be used to set pixel values.

-nrows nrows and -ncolumns ncolumns

Specify the size of the synthesized image. Default: 256 rows and columns.

-repn bit | ubyte | sbyte | short | long | float | double

Specifies the pixel representation of the synthesized image. Default: float.

-name name

Specifies the name to be given the synthesized image. Default: ``image''.

The output file can be specified on the command line or allowed to default to the standard output stream.

PATTERNS

The -pattern option specifies which of the following patterns is used to initialized pixel values. For each type of pattern there are additional options that may be used to specify pattern parameters. In general, numeric parameters are not restricted to just integer values.

Constant

  -pattern constant
 [-base b]                 Default: 0.
 

All pixel values are set to b.

Impulse

  -pattern impulse
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 0.
 [-origin i j]             Default: image center.
 

The pixel at row i, column j is set to a; all others are set to b. (i and j are truncated to integers.)

Ramp

  -pattern ramp
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 0.
 [-origin i j]             Default: image center.
 [-orientation d]          Default: 0.
 

The image is filled with a ramp whose slope is a units per pixel. The ramp is centered at row i, column j, where it has the value b. The ramp increases in the direction d, which is measured CCW in degrees from the direction of increasing column number.

Sine Grating

  -pattern sine
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 0.
 [-origin i j]             Default: image center.
 [-phase w]                Default: 0.
 
     and one of
         [-frequency f]    Default: 0.
         [-orientation d]  Default: 0.
     or
         [-period t]       Default: 8.
         [-orientation d]  Default: 0.
     or
         [-xfreq x]        Default: 0.
         [-yfreq y]        Default: 0.
 
 

The image is filled with a sine grating. The grating has a DC component of b and an amplitude of a (or 2a peak-to-peak). Its frequency and direction may be specified by any of three combinations of frequency (in cycles per pixel, measured either in the direction of the grating or as horizontal and vertical components), period (in pixels per cycle), and orientation (in degrees CCW from the direction of increasing column number). The grating is shifted so that at row i, column j it has phase w radians.

Zone Plate

  -pattern zone
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 0.
 [-origin i j]             Default: image center.
 [-period t]               Default: 8.
 [-phase w]                Default: 0.
 

The image is filled with the zone plate pattern defined by f(r) = a cos(r^2/t + w) + b, where r is the radial distance from the origin at row i, column j.

Uniformly Distributed Noise

  -pattern uniform
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 1.
 [-seed s]                 Default: a random number.
 

Pixels are set to random values drawn independently from [b,b+a] according to a uniform distribution. The random number generator is initialized with the seed s.

Normally Distributed Noise

  -pattern normal
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 1.
 [-seed s]                 Default: a random number.
 

Pixel values are set to random values drawn independently according to a normal (Gaussian) distribution with mean b and standard deviation a. The random number generator is initialized with the seed s.

Binomially Distributed Noise

  -pattern binomial
 [-amplitude a]            Default: 1.
 [-base b]                 Default: 1.
 [-density p]              Default: 0.5.
 [-seed s]                 Default: a random number.
 

Pixel values are drawn at random from a binomial distribution. A pixel is given the value b with probability 1 -p, and it is given the value b+a with probability p.

SEE ALSO

VImage(3Vi), Vista(7Vi)

AUTHOR

Art Pope <pope@cs.ubc.ca>