ff-dntsc.1

.Dd 2024-05-07
.Dt FF-DNTSC 1
.Os farbfeld-utils
.Sh NAME
.Nm ff-dntsc
.Nd farbfeld filter program that decodes NTSC colours
.Sh SYNOPSIS
.Nm
<?opt=value?> ... <?opt=value?>
.Sh DESCRIPTION
.Nm
reads NTSC colour information from stdin, converts it to
.Xr farbfeld 5
RGB and writes the result to stdout.
.Pp
This program does not decode the NTSC frame.
.Pp
In case of an error
.Nm
writes a diagnostic message to stderr.
.Sh EXIT STATUS
.Bl -tag -width Ds
.It 0
Image processed successfully.
.It 1
An error occurred.
.El
.Sh OPTIONS
The filter takes zero or more arguments that set values for options.

Arguments consist of a single letter or number, followed by a equal sign,
followed by the value. The value can be a number, which may be positive or
negative, and some options may include a fractional part.

Only the red channel of the input is used to make the colours of the output;
the alpha channel of input is just copied to output, while the green and blue
channels of input are ignored.

Valid options include:
   1 to 6 = coefficients for the equation to convert YIQ to RGB
            (0.966882, 0.623557, -0.274788, -0.635691, -1.108545, 1.709007)
   a = border voltage (0.0)
   c = total contrast amount (0.009574) (all outputs are multiplied by this)
   f = phase finetune (in radians) (0.0)
   h = the voltage that a white pixel represents (92.0)
   i = amount of spread of the I component (24)
   l = the voltage that a black pixel represents (-11.0)
   m = initial phase (0.0)
   p = phase adjust per scanline (0.0) (should be nonzero for Famicom)
   q = amount of spread of the Q component (24)
   s = saturation amount (0.8)
   t = colour subcarrier width (12.0)
   v = quadrature shift (3/4 of the value of t)
   y = amount of spread of the Y component (12.0)
   z = if nonzero, the output format is YIQ instead of RGB (0)

NB: there is no option to detect a burst signal.

Unclear if it is the intended usage, but you can try passing a normal image
through this filter for interesting effects.
.Sh EXAMPLES
$
.Nm
< image.ff > image-ntsc.ff
.Sh SEE ALSO
.Xr farbfeld 5 ,
.Xr farbfeld-utils 7