#!/usr/bin/perl -w use strict; # Convert quadrilateral to square use Imager; my $src=Imager->new(); $src->open(file=>"oldmap_200px.jpg"); # example co-ordinates of quadrilateral my $x0=12; my $y0=4; # top left my $x1=157; my $y1=0; # top right my $x2=140; my $y2=150; # bottom right my $x3=27; my $y3=159; # bottom left my $code=<<EOF; xa=((h-y)*x0+y*x3)/h; ya=((h-y)*y0+y*y3)/h; xb=((h-y)*x1+y*x2)/h; yb=((h-y)*y1+y*y2)/h; xc=((w-x)*x0+x*x1)/w; yc=((w-x)*y0+x*y1)/w; xd=((w-x)*x3+x*x2)/w; yd=((w-x)*y3+x*y2)/w; d=det(xa-xb,ya-yb,xc-xd,yc-yd); d=if(d==0,1,d); px=det(det(xa,ya,xb,yb),xa-xb,det(xc,yc,xd,yd),xc-xd)/d; py=det(det(xa,ya,xb,yb),ya-yb,det(xc,yc,xd,yd),yc-yd)/d; return getp1(px,py); EOF my $newimg=Imager::transform2({ expr=>$code, width=>200, height=>200, constants=>{x0=>$x0,y0=>$y0, x1=>$x1,y1=>$y1, x2=>$x2,y2=>$y2, x3=>$x3,y3=>$y3}}, ($src)); $newimg->write(file=>"output_imager.jpg"); =head1 NAME quad_to_square.pl - transform an arbitrary quadrilateral to a square. =head1 SYNOPSIS perl quad_to_square.pl =head1 DESCRIPTION =for stopwords Fairhurst resized Courtesy Richard Fairhurst: I've been using it to rectify ("square up") a load of roughly scanned maps, so that an arbitrary quadrilateral is resized into a square. The transform2 function is ideal for that. Thought you might be interested to see what people are doing with Imager - feel free to include this in the sample code. =head1 AUTHOR Richard Fairhurst =cut