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Pamperspective User Manual(0)                    Pamperspective User Manual(0)



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  corre-
       sponds to a parallelogram in the painting.  The output image consists of this parallelogram, sheared to a rect-
       angle.  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  dif-
       ferent 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 Out-
       put.



OPTIONS
       For options of the form --name=num, You can specify the value num in any of the  traditional  ways.   Addition-
       ally,  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,
       --frame_include,  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), 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.



netpbm documentation           2 September 2004  Pamperspective User Manual(0)