% uses element_at/3, length/2 from file 'list.p'
% please: consult('../util/list.p').
% In the image processing examples, several representations are
% used for pixel images.
%
% This file gives the simplest representation.
% The file 'gimage.p' describes the more complicated 'gimage'
% representation which is used in the definition of various filters.
% The file 'eximages.p' has the example images from figures in chapter 8.
% The simplest and most important representation is a double list
% (list of lists) of pixel values.
% In particular, this is most useful for input/output.
%
% For example the image in figure 8.2 (page 166) is represented as:
%
% image('figure 8.2', 15, 12,
% [ [ 0,0,0,0,0,1,2,2,0,0,0,0,0,0,0 ],
% [ 0,0,0,0,0,4,6,6,5,1,0,0,0,0,0 ],
% [ 0,0,0,0,5,5,6,6,6,6,8,8,8,5,0 ],
% [ 0,0,0,0,5,5,6,6,6,6,8,9,9,6,0 ],
% [ 0,0,1,1,6,6,6,6,6,6,8,9,9,6,0 ],
% [ 0,0,1,1,5,6,6,6,6,5,2,9,9,6,0 ],
% [ 0,0,1,1,1,3,6,5,4,1,1,9,9,6,0 ],
% [ 0,0,1,1,1,1,1,1,1,1,1,9,9,6,0 ],
% [ 0,0,1,1,1,1,1,1,1,1,1,8,8,5,0 ],
% [ 0,0,1,1,1,1,1,1,1,1,1,1,6,6,0 ],
% [ 0,0,1,1,0,0,0,1,1,1,0,1,0,0,0 ],
% [ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ]
% ] ).
%
% This definition can be found in the file 'eximages.p'
% The predicates image_at/4 and raw_image_at/4 extract the pixel at
% particular coordinates of an image. The difference is that
% raw_image_at is undefined outside the boundaries of the image
% whereas image_at returns zero.
image_at( Image, X, Y, Pixel ) :-
image_size(Image,Wid,Ht),
image_at1( Image, Wid, Ht, X, Y, Pixel ).
image_at1( Image, Wid, Ht, X, Y, 0 ) :-
nonvar(X), (X<1 ; X>Wid), !. % out of bounds
image_at1( Image, Wid, Ht, X, Y, 0 ) :-
nonvar(Y), (Y<1 ; Y>Ht), !. % out of bounds
image_at1( Image, Wid, Ht, X, Y, Pixel ) :-
raw_image_at( Image, X, Y, Pixel ).
raw_image_at( Image, X, Y, Pixel ) :-
element_at(Image,Y,Scan_Y),
element_at(Scan_Y,X,Pixel).
% image_size/3 is used to calculate the width and height of an image
% and also to create empty images of a given size.
% The definition has to be carefully constructed to allow this
% polymorphic use, hence it the first clause is not the more obvious
% definiton of:
% length( Image, Ht ),
% element_at(Image, 1, First_Row),
% length( First_Row, Wid ).
% This would have only fixed the width of the first row of the image.
% Note that because the definition below examines EVERY row, the predicate
% only suceeds if the image is well formed and all the rows are of the
% same length.
image_size( Image, Wid, Ht ) :-
length( Image, Ht ),
image_wid( Image, Wid ).
image_wid( [], Wid ).
image_wid( [Row|Image], Wid) :-
length( Row, Wid ),
image_wid( Image, Wid ).
image_wid2( Image, Row, Wid, Ht ) :- % N.B. Row is always ground
Row >= Ht, !.
image_wid2( Image, Row, Wid, Ht ) :-
element_at(Image, Row, Scan_Row),
length( Scan_Row, Wid ),
Row1 is Row + 1,
image_wid2( Image, Row1, Wid, Ht ).
% RUNNING THIS CODE
%
% Try some small examples first:
%
%> image_size( [[0,1,0],[0,2,1]], Wid, Ht ).
%
%> image_size( L, 5, 3 ). % creates an empty 5 x 3 image
%
%> image_at( [[1,2,3],[4,5,6],[7,8,9]], 2, 3, P ).
%
%> raw_image_at( [[1,2,3],[4,5,6],[7,8,9]], 4, 2, P ).
%
%> image_at( [[1,2,3],[4,5,6],[7,8,9]], 4, 2, P ).
%
% Look at 'eximages.p' for larger examples. Compare each one with
% the corresponding example in the book.
% Consult the file:
% consult('eximages.p').
%
% and then try retreiving images:
%> image('figure 8.2', Wid, Ht, Image).
%
% and finally use image_size and image_at on them
%> image('figure 8.2', Wid, Ht, Image),
%+ image_size( Image, W, H ), % I hope the same as Wid and Ht!!
%+ image_at( Image, 11, 7, P ).
% EXAMPLES
%
%> image_size( [[0,1,0],[0,2,1]], Wid, Ht ).
%
%> image_size( L, 5, 3 ). % creates an empty 5 x 3 image
%
%> image_at( [[1,2,3],[4,5,6],[7,8,9]], 2, 3, P ).
%
%> raw_image_at( [[1,2,3],[4,5,6],[7,8,9]], 4, 2, P ).
%
%> image_at( [[1,2,3],[4,5,6],[7,8,9]], 4, 2, P ).
%
%> image('figure 8.2', Wid, Ht, Image).
%
%> image('figure 8.2', Wid, Ht, Image),
%+ image_size( Image, W, H ), % I hope the same as Wid and Ht!!
%+ image_at( Image, 11, 7, P ).
