Provided by: netpbm_11.01.00-2build1_amd64 bug

NAME

       pamperspective - a reverse scanline renderer for Netpbm images

SYNOPSIS

       pamperspective
           [--bottom_margin=num]
           [--detail=num]
           [--frame_include=bool]
           [--height=num]
           [--include=[x1,y1;x2,y2; ...]]
           [--input_system=spec]
           [--input_unit=spec]
           [--interpolation=spec]
           [--left_margin=num]
           [--margin=num]
           [--output_system=spec]
           [--proportion=spec]
           [--ratio=num]
           [--right_margin=num]
           [--top_margin=num]
           [--width=num]
           {
             {
               upper_left_x upper_left_y upper_right_x upper_right_y
               lower_left_x lower_left_y lower_right_x lower_right_y
             }
             |
             {
               {--upper_left_x|--ulx}=upper_left_x
               {--upper_left_y|--uly}=upper_left_y
               {--upper_right_x|--urx}=upper_right_x
               {--upper_right_y|--ury}=upper_right_y
               {--lower_left_x|--llx}=lower_left_x
               {--lower_left_y|--lly}=lower_left_y
               {--lower_right_x|--lrx}=lower_right_x
               {--lower_right_y|--lry}=lower_right_y
             }
          }
          [infile]

OPTION USAGE

       Minimum  unique  abbreviation  of  option  is  acceptable.  (But note that shortest unique
       prefixes might be longer in future versions of the program.) You may  use  single  hyphens
       instead of double hyphen to denote options. You may use white space in place of the equals
       sign to separate an option name from its value. All options starting with hyphens  may  be
       given in any order.

DESCRIPTION

       This program is part of Netpbm(1).

       pamperspective  reads  a  Netpbm  image  as  input and produces a Netpbm image of the same
       format as output.

       pamperspective interprets the input image as a perspective  projection  of  another  image
       which  is  in  a plane oblique to that of the input image.  For example, a photograph of a
       painting, taken at an angle.  The  arguments  upper_left_x  ...  lower_right_y  specify  a
       quadrilateral in the photograph that pamperspective assumes corresponds to a parallelogram
       in the painting.  The output image consists of this parallelogram, sheared to a rectangle.
       In this way pamperspective undoes the effect of a raytracer or scanline renderer.

       Note  that  if  the input image is a projection of a solid scene, rather than a plane, the
       result is like a different camera angle on that scene, to the extent  that  the  scene  is
       shallow from the other angle.

       The  input is from infile, or from Standard Input, if infile is not specified.  The output
       is to Standard Output.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common  Options  ⟨index.html#commonoptions⟩  ),  pamperspective  recognizes the following
       command line options:

       For options of the form  --name=num,  You  can  specify  the  value  num  in  any  of  the
       traditional  ways.  Additionally, you can specify it as num1/num2, where num1 and num2 are
       specified traditionally.  This is useful for  specifying  a  width/height  ratio  of  4/3,
       without  having  to  write  infinitely many digits.  Where num is supposed to be a natural
       number, pamperspective does not allow this format.

   Quadrilateral Specification Options
       --upper_left_x=num

       --ulx=num

              This specifies the horizontal coordinate of the upper left
                vertex of the quadrilateral.  The meaning of 'upper left' is
                relative to the output image.  The interpretation of num
                depends on the values for --input_system and
                --input_unit.

       --upper_left_y=num

       --uly=num

              This specifies the vertical coordinate of the upper left vertex
                of the quadrilateral.  The meaning of 'upper left' is relative to
                the output image.  The interpretation of num depends on the
                values for --input_system and --input_unit.

       --upper_right_x=num

       --urx=num

              This specifies the horizontal coordinate of the upper right
                vertex of the quadrilateral.  The meaning of 'upper right' is
                relative to the output image.  The interpretation of num
                depends on the values for --input_system and
                --input_unit.

       --upper_right_y=num

       --ury=num

              This specifies the vertical coordinate of the upper right vertex
                of the quadrilateral.  The meaning of 'upper right' is relative to
                the output image.  The interpretation of num depends on the
                values for --input_system and --input_unit.

       --lower_left_x=num

       --llx=num

              This specifies the horizontal coordinate of the lower left
                vertex of the quadrilateral.  The meaning of 'lower left' is
                relative to the output image.  The interpretation of num
                depends on the values for --input_system and
                --input_unit.

       --lower_left_y=num

       --lly=num

              This specifies the vertical coordinate of the lower left vertex
                of the quadrilateral.  The meaning of 'lower left' is relative to
                the output image.  The interpretation of num depends on the
                values for --input_system and --input_unit.

       --lower_right_x=num

       --lrx=num

              This specifies the horizontal coordinate of the lower right
                vertex of the quadrilateral.  The meaning of 'lower right' is
                relative to the output image.  The interpretation of num
                depends on the values for --input_system and
                --input_unit.

       --lower_right_y=num

       --lry=num

              This specifies the vertical coordinate of the lower right vertex
                of the quadrilateral.  The meaning of 'lower right' is relative to
                the output image.  The interpretation of num depends on the
                values for --input_system and --input_unit.

       --input_system=system

       --input_unit=unit

              The input image consists of pixels, which are, from the point of
                view of a scanline renderer, solid squares.  These options specify
                how the coordinates are interpreted:

       system=lattice, unit=image

              (0,0) refers to the upper left corner of the upper left pixel
                  and (1,1) refers to the lower right corner of the lower right
                  pixel.

       system=lattice, unit=pixel

              (0,0) refers to the upper left corner of the upper left pixel
                  and (width,height) refers to the lower right corner
                  of the lower right pixel.  Here width and height are
                  the width and height of the input image.

       system=pixel, unit=image

              (0,0) refers to the center of the upper left pixel and (1,1)
                  refers to the center of the lower right pixel.

       system=pixel, unit=pixel

              (0,0) refers to the center of the upper left pixel and
                  (width-1,height-1) refers to the center of the lower
                  right pixel.  Here width and height are the width
                  and height of the input image.

                The defaults are --input_system=lattice and
                --input_unit=pixel.  Point-and-click front ends should
                use --input_system=pixel.

   Frame Options
       By default pamperspective outputs exactly the above parallelogram, sheared to a rectangle.
       With  the  following  options,  it  is  possible to make pamperspective output a larger or
       smaller portion, which we call the "visible part." We refer to the  default  rectangle  as
       the  "frame."  The  visible  part  is always a rectangle the axes of which are parallel to
       those of the frame.

       The frame options are additive.  All the parts of the image  specified  by  either  margin
       options,  --include_frame,  or --include (or their defaults) are in the visible part.  The
       visible part is the smallest possible rectangle that contains the  parts  specified  those
       three ways.

       The  visible  part  must  have nonzero size.  That means if you specify --frame_include=no
       (overriding the default), you'll need to specify other frame  options  in  order  to  have
       something in the visible part.

       [--margin=num]

              This specifies an area surrounding the frame that is to be
                included in the visible part.  The units of num are the width
                of the frame for the horizontal extensions and the height of the
                frame for vertical extensions.

              For example, --margin=1 makes the visible part 9 times as large,
                because it makes the visible part extend one frame's worth to the left
                of the frame, one frame's worth to the right, one frame's worth above
                the frame, and one frame's worth below the frame, for a total of
                3 frames' worth in both dimensions.

              A negative value has an effect only if you specify
                --frame_include=no.  The default is no margin.

              The individual margin options below override this common margin
                setting.

       [--top_margin=num]

       [--left_margin=num]

       [--right_margin=num]

       [--bottom_margin=num]

              These are like --margin, but they specify only one of
                the 4 sides.  The default value for each is the value (or default) of
                --margin.

       [--frame_include=bool]

              Valid values for bool are:

       yes

       true

       on

              The frame itself is in the visible part.

       no

       false

       off

              The frame itself is not necessarily in the visible part
                  (but it could be if other options cause it to be).

                The default value is yes

       --include=[x1,y1;x2,y2; ...]

              The visible part is made large enough such that every point
                (x1,y1), (x2,y2), of the input image is
                visible.  The meaning of x and y is determined by
                --input_system and --input_unit.  You can specify any
                number of semicolon-delimited points, including zero.

              If you're supplying these options via a Unix command shell, be
                sure to use proper quoting, because semicolon (;) is usually
                a shell control character.

       The frame options were new in Netpbm 10.25 (October 2004).

   Output Size Options
       --width=width

       --height=height

              These specify the size of the output image in horizontal and
                vertical direction.  The values are numbers of pixels, so only
                natural numbers are valid.  These values override the default
                means to determine the output size.

       --detail=num

              If you do not specify --width, pamperspective
                determines the width of the output image such that moving num
                output pixels horizontally does not change the corresponding pixel
                coordinates of the input image by more than 1.
                pamperspective determines the height of the output image
                analogously.  The default value is 1.

       --proportion=prop

       --ratio=ratio

              Valid values for prop are:

       free

              In this case --ratio does not have any effect.

       fixed  After the width and height are determined
                  according to --detail, one of both will be increased, in
                  order to obtain width/height=ratio.

                The defaults are --proportion=free and
                --ratio=1.

   Output Options
       --output_system=spec

              The output image consists of pixels, which are, from the point
                of view of a scanline renderer, solid squares.  This option
                specifies how the four vertices of the quadrilateral correspond to
                the pixels of the output image.  Valid values for spec are:

       lattice

              The upper left vertex corresponds to the upper left corner of
                  the upper left pixel and The lower right vertex corresponds to the
                  lower right corner of the lower right
                  pixel.

       pixel

              The upper left vertex corresponds to the center of the upper
                  left pixel and The lower right vertex corresponds to the center of
                  the lower right pixel.

                The default value is lattice.  Point-and-click front ends
                should use pixel.

       --interpolation=spec

              Usually (centers of) output pixels do not exactly correspond to
                (centers of) input pixels.  This option determines how the program
                will choose the new pixels.  Valid values for spec are:

       nearest

              The output pixel will be identical to the nearest input
                  pixel.

       linear

              The output pixel will be a bilinear interpolation of the four
                  surrounding input pixels.

                The default value is nearest.

HINTS

       It  might  be  tempting  always  to  use  the  options --include 0,0;0,1;1,0;1,1 (assuming
       --input_system=lattice and --input_unit=image), so that no part  of  the  input  image  is
       missing in the output.  There are problems with that:

       •      If the three dimensional plane defined by the quadrilateral has a
                visible horizon in the input image, then the above asks pamperspective
                to include points that cannot ever be part of the output.

       •      If the horizon is not visible, but close to the border of the
                input image, this may result in very large output
                files. Consider a picture of a road. If you ask for a point close to
                the horizon to be included, then this point is far away from the
                viewer. The output will cover many kilometers of road, while
                --detail perhaps makes a pixel represent a square centimeter.

       When  working  with large files pamperspective's memory usage might be an issue.  In order
       to keep it small, you should minimize each of the following:

       •      The vertical range that the top output line consumes in the
                input image;

       •      The vertical range that the bottom output line consumes in the
                input image;

       •      The vertical range from the topmost (with respect to the
                input image) quadrilateral point to the top (with respect to the output
                image) output line.

              For this purpose you can use pamflip before and/or after  pamperspective.  Example:
              Instead of

              pamperspective 10 0 100 50 0 20 95 100 infile > outfile

              you can use

              pamflip -rotate90 infile |
                 pamperspective 50 0 100 5 0 90 20 100 |
                 pamflip -rotate270 > outfile

SEE ALSO

       netpbm(1),  pam(1), pnm(1), pamcut(1), pamflip(1), pnmrotate(1), pamscale(1), pnmshear(1),
       pamhomography(1), pnmstitch(1)

HISTORY

       Mark Weyer wrote pamperspective in March 2004.

       It was new in Netpbm 10.22 (April 2004).

AUTHOR

       This documentation was written by Mark Weyer.  Permission is granted to  copy,  distribute
       and/or  modify  this document under the terms of the GNU General Public License, Version 2
       or any later version published by the Free Software Foundation.

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master
       documentation is at

              http://netpbm.sourceforge.net/doc/pamperspective.html