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Adjust the display resolution of an image

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Adjust the display resolution of an image


Eric Johnson


24 Aug 2008 (Updated )

Same as TRUESIZE, but works with multi-image figures.

truefit(h, pxArea)
function truefit(h, pxArea)
%TRUEFIT resizes an image axes to display at a particular resolution. Extends
%the functionality of TRUESIZE, which only works with single-image figures.
%   TRUEFIT(H, [MROW NCOL]) adjusts the display size of an image. H is the
%   handle of an image object or an axes that containins one.[MROW NCOL]
%   specifies the requested screen area (in pixels) that the image should be
%   displayed at.
%   TRUEFIT(H) uses the image's height and width for [MROW NCOL]. This results
%   in the display having one screen pixel for each image pixel.
%   The center of the axes' position rectangle will remain constant relative to
%   the object that contains it (i.e., its parent figure or UICONTROL). The axes
%   is "pinned" at its center.
%   Example
%   --------
%       % Load the 'cameraman' image
%       img = imread('cameraman.tif');
%       % Plot image, initially as large as possible.
%       h1 = imshow(img,'InitialMagnification','fit');
%       % Now resize to match the screen resolution
%       truefit(h1);

%   Eric C. Johnson <>    10-Jul-2008
%   Copyright 1984-2008 The MathWorks, Inc.
%   This function is not supported by The MathWorks, Inc.
%   It is provided 'as is' without any guarantee of
%   accuracy or functionality.

% Is H an axes or image handle?
switch lower( get(h,'type') )            
    case 'axes'
        % Find image object handle from axes
        hAxes   = h;
        hImg    = findobj(hAxes,'type','image');
        % Verify that axes contains a single image plot object
        if isempty(hImg)
            error('MATLAB:truefit','No image objects found in axes.');
        elseif length(hImg) > 1
            error('MATLAB:truefit','Axes should contain only a image object.');
    case 'image'
        hImg = h;
        hAxes = get(h,'Parent');

% Determine new display size
if nargin < 2
    % Use 1:1 image pixel to screen pixel ratio. Need to get the dimensions of
    % the image object. 
    cdata = get(hImg,'cdata');    
    [mrow,ncol] = size(cdata);
    % User provided display size
    mrow = pxArea(1);
    ncol = pxArea(2);

% Now set axes size to match [MROW NCOL]
% Temporarily change axes units to pixels
oldunits = get(hAxes,'Units');    

% Collect axes positioning information
oldpos = get(hAxes,'Position');

% Width and height are known from CDATA, however the lower left corner of
% the axes must be recomputed.
newleft = (oldpos(1) + oldpos(3)/2) - ncol/2;
newbot  = (oldpos(2) + oldpos(4)/2) - mrow/2;

newpos = [newleft newbot ncol mrow];

% Apply new position and restore original units

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