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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 pre-
       fixes 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 for-
       mat 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
       For options of the form --name=num, You can specify the value num in  any  of  the  tradi-
       tional ways.  Additionally, you can specify it as num1/num2, where num1 and num2 are spec-
       ified 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:

       o      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.

       o      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:

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

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

       o      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) , pnms-
       hear(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)
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