.help hdtoi May88 imred.dtoi
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NAME
hdtoi -- transform images according to hd curve
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USAGE
hdtoi input output database
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PARAMETERS
.ls input
List of images to be transformed.
.le
.ls output
List of output image names.
.le
.ls database
Name of text database describing HD curve.
.le
.ls fog = ""
Value of fog level, read from database if unspecified.
.le
.ls option = "mean"
Option for calculating fog density when \fBfog\fR is a file list, can be
either "mean" or "median".
.le
.ls sigma = 3.0
If \fBfog\fR is a file name, and \fBoption\fR = "mean", the mean fog density
is iteratively calculated using this rejection criteria.
.le
.ls floor = 0.0
Value assigned to levels below fog, can be either 0.0 or -1.0.  
.le
.ls ceiling = 30000.
The final intensities are scaled to this value, such that a saturated
input density equals \fBceiling\fR on output.
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.ls datatype = "r"
Datatype of output image pixels.
.le
.ls verbose = yes
Print log of processing to STDOUT.
.le
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DESCRIPTION
Task \fIhdtoi\fR transforms one image to another as described by the 
\fBdatabase\fR.  There is only one HD curve per run; the same 
transformation is applied to all input images.

The fog value can be obtained in three ways: read from the database, read
as a floating point number, or calculated from a list of fog images.  If 
parameter \fBfog\fR is not specified, the fog value is read from 
\fBdatabase\fR.  If \fBfog\fR is specified, it can be entered
as either a floating point number or as a list of file names.  If the
value cannot be read as a number, it is assumed to be a file name.  In that
case, the density of each file in the fog list is calculated and the 
average of these values is subtracted from \fBinput\fR before processing.
The algorithm used to calculate the fog density is selected by the
\fBoption\fR parameter, and is either a "mean" or "median" calculation.
The fog density can be the mean value after pixels more than the specified
number of sigma have been rejected, or the median value of all the fog spot
pixels.

The fog value is subtracted from the input image before the transformation
takes place.  It is possible that some density values will fall below
the fog level; these values are handled in one of two ways.  Values
below the fog value are set equal to 0.0 when \fBfloor\fR = 0.0.  If 
\fBfloor\fR = -1.0, the resulting intensity = -1 * intensity (abs (value)).

A scaling factor is applied to the final intensities, as typically
they will be < 1.0.  The \fBceiling\fR parameter is used to specify what
value a saturated density is transformed to; all intensities are scaled
to this upper limit.  The precision of the transformation is unaffected by 
this parameter, although caution must be used if the output image pixel
type is an integer.  The user is responsible for choosing
a \fBceiling\fR that avoids the truncation of significant digits.
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EXAMPLES
Convert three density images to intensity images as described in database db1.

	cl> hdtoi denin* intim1,intim2,intim3 db1
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TIME REQUIREMENTS
Task \fBhdtoi\fR requires 20 cpu seconds to transform a 512 square image, with
a 12 bit data range, on a VAX 750
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SEE ALSO
spotlist, dematch, hdfit
.endhelp