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.\" RCSid "$Id: rcrop.1,v 1.8 2023/12/12 16:31:45 greg Exp $"
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.TH RCROP 1 3/14/2022 RADIANCE
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.SH NAME
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rcrop - crop RADIANCE matrix or picture
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.SH SYNOPSIS
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.B "rcrop row0 col0 nrows ncols"
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[
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.B input
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[
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.B output
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]
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]
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.SH DESCRIPTION
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.I Rcrop
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copies the indicated section of a matrix or RADIANCE picture.
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The four required arguments are the initial row (scanline) to copy,
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the initial column, the number of rows to copy, and the number of columns
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to include per row.
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Note that rows are numbered from 0 at the top of a matrix or picture,
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and columns are changing fastest in the input, which can have any number
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of components per matrix element.
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.PP
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The input must have a valid header, including dimensions and format,
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and a header will always be produced.
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This is similar behavior to
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.I rmtxop(1).
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If the input header is missing, one can usually be added with an
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appropriate call to
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.I rcollate(1).
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If an output header is not desired, it can be removed using
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.I getinfo(1).
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.PP
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One cannot specify crop boundaries outside the matrix dimension limits.
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If a 0 value is specified for the number of rows to copy, then all rows
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will be copied, starting from row0.
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Similarly, a 0 value for the number of columns to copy implies all
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columns >= col0 will be copied.
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A negative count for the number of rows or columns cuts the
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corresponding amount off the end(s).
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.PP
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Using
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.I rcrop
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on a RADIANCE picture rather than
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.I pcompos(1)
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corrects the view parameters if present,
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and preserves the exposure in a way that is compatible with
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.I evalglare(1).
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However, one must remember that rows correspond to Y
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coordinates, and the orientation is reversed from a standard
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picture, where Y=0 is the bottom scanline.
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Spectral pictures, as might be produced by
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.I rtrace(1)
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or
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.I rfluxmtx(1),
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are also supported.
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.PP
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All matrix formats are supported, including text (ASCII), binary float
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and double.
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The
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.I rcrop
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tool also works on encoded normal vector files produced by
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.I rcode_norm(1)
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and encoded depth files produced by
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.I rcode_depth(1).
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Data is copied verbatim, i.e., there is no internal conversion to
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another representation, although white space may change in text files.
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.PP
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If no input file is given, data will be taken from the standard input.
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If no output file is specified, data will be copied to the standard output.
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.SH EXAMPLES
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To crop a matrix down to 15 rows by 19 columns,
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starting at row 10 and column 12:
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.IP "" .2i
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rcrop 10 12 15 19 input.mtx > output.mtx
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.PP
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To extract column 35 from a matrix:
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.IP "" .2i
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rcrop 0 35 0 1 orig.mtx > col35.mtx
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.PP
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To crop a picture to (X by Y) = (1500 by 1000),
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starting from upper-left corner:
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.IP "" .2i
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rcrop 0 0 1000 1500 orig.hdr cropped.hdr
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.PP
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Two ways of computing the inner product of row 15 in matrix 1 by
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column 27 in matrix 2 and extracting the result without a header,
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the second command being more efficient:
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.IP "" .2i
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rmtxop -fa mat1.mtx mat2.mtx | rcrop 15 27 1 1 | getinfo -
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.IP "" .2i
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rmtxop -fa '!rcrop 15 0 1 0 mat1.mtx' '!rcrop 0 27 0 1 mat2.mtx' | getinfo -
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.SH AUTHOR
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Greg Ward
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.SH "SEE ALSO"
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evalglare(1), pcompos(1), rcalc(1), rcode_depth(1), rcode_norm(1),
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rcollate(1), rcomb(1), rfluxmtx(1), rmtxop(1), rsplit(1), rtrace(1)
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