UPSCALEXY - Image upsampling.

Description
Syntax
Inputs
Outputs
See also
Function implementation

Description

Upsample monotically the input (possibly multispectral) image by either duplicating, interpolating or inserting 0's between its input samples in both X- and Y-directions.

Syntax

     upI = UPSCALEXY(I)
     upI = UPSCALEXY(I, [sx sy], method)

Inputs

I : 2D or 3D input matrix with size (X,Y,Z) to be upsampled in X- (vertical) and Y- (horizontal) directions.

sx, sy : size (multiplicating factor) of the upsampling in X- and Y- directions; default: sx=sy=2.

method : method used for upsampling, wich is either interpolation or duplication; it can be either of:

'cubic', 'linear', 'nearest', 'splines' or 'spline' (call INTERP2) if the matrix I is interpolated so that each block of the form [((i-1)*sx+1):(i*sx), ((j-1)*sy+1):(j*sy)] of the output matrix is a quadratic interpolation between the values I(i,j), I(i+1,j), I(i,j+1) and I(i+1,j+1) by the selected method.
'replicate' if the entries of the matrix are duplicated sx times in X-direction and sy times in Y-direction so that each block [((i-1)*sx+1):(i*sx), ((j-1)*sy+1):(j*sy)] of the output matrix is filled with the identical value I(i,j); creates a pixelized image,
'upsample' to upsample the image sx times in X-direction and sy times in Y-direction by inserting 0 between the input samples, similarly to the function UPSAMPLE;

default: method='replicate'.

Outputs

upI : the upsampled matrix with size (sx*X,sy*Y,Z).

Function implementation

function upI = upscalexy(I,varargin)

parsing parameters

error(nargchk(1, 11, nargin, 'struct'));
error(nargoutchk(1, 1, nargout, 'struct'));

if ~isnumeric(I) && ~islogical(I)
    error('upscalexy:errorinput','matrix required in input');
end

% optional parameters
p = createParser('UPSCALEXY');   % create an instance of the inputParser class.
p.addOptional('S', [2 2 1], @(x)isnumeric(x) && all(x>=1) && length(x)<=3);
p.addOptional('method','replicate', @(x) ischar(x) && ...
    any(strcmp(x,{'cubic','linear','spline','nearest','replicate','upsample'})));

% parse and validate all input arguments
p.parse(varargin{:});
p = getvarParser(p);

main computation: upscaling

upI = upscalexy_base(I, p.S, p.method);

display

if p.disp
    figure,
    [X,Y,C] = size(I);
    B = zeros(size(upI));
    for ic=1:C
        B(1:X,1:Y,ic) = I(:,:,ic);
    end
    subplot(1,2,1), imagesc(rescale(B,0,1)), axis image off, title('original');
    subplot(1,2,2), imagesc(rescale(upI,0,1)), axis image off, title('upscaled');
    if size(upI,3)==1,  colormap gray;  end
end

end % end of upscalexy