function [info,msg] = imicoinfo(filename)
%IMICOINFO Get information about the image in an ICO file.
%   [INFO,MSG] = IMICOINFO(FILENAME) returns information about
%   the image contained in an ICO file containing one or more
%   Microsoft Windows icon resources.  If the attempt fails for
%   some reason (e.g. the file does not exist or is not an ICO
%   file), then INFO is empty and MSG is a string containing a
%   diagnostic message.
%
%   See also IMREAD, IMWRITE, IMFINFO.

%   Copyright 1984-2000 The MathWorks, Inc.
%   $Revision: 1.3 $  $Date: 2000/06/23 15:37:51 $
%   $ Revision $  $ Date $

% This function should not call error()!

info = [];
msg = '';

if (~ischar(filename))
    msg = 'FILENAME must be a string';
    return;
end

[fid, m] = fopen(filename, 'r', 'ieee-le');  % ICO files are little-endian
if (fid == -1)
    info = [];
    msg = m;
    return;
end
filename = fopen(fid);  % Get the full path name if not in pwd
d = dir(filename);      % Read directory information

%
% Initialize universal structure fields to fix the order
%
info.Filename = filename;
info.FileModDate = d.date;
info.FileSize = d.bytes;
info.Format = 'ico';
info.FormatVersion = [];
info.Width = [];
info.Height = [];
info.BitDepth = [];
info.ColorType = [];
info.FormatSignature = [];

%
% Initialize ICO-specific structure fields to fix the order
%
info.NumColormapEntries = [];
info.Colormap = [];

% Read the resource header to verify the correct type
sig = fread(fid, 2, 'uint16');
if (isempty(sig))
    info = [];
    msg = 'Empty file';
    fclose(fid);
    return;
end
    
if (~isequal(sig, [0; 1]))
    info = [];
    msg = 'Not an ICO file.';
    fclose(fid);
    return;
end

% Find the number of icons in the file
imcount = fread(fid, 1, 'uint16');

for p = 1:imcount
    info(p).Filename = filename;
    info(p).FileModDate = d.date;
    info(p).FileSize = d.bytes;
    info(p).Format = 'ico';
    info(p).FormatSignature = sig';

    % Offset to the current icon directory entry
    idpos = 6 + 16*(p - 1);
    fseek(fid, idpos, 'bof');
    
    % Read the icon directory
    info(p).Width = fread(fid, 1, 'uint8');
    info(p).Height = fread(fid, 1, 'uint8');
    
    fseek(fid, 6, 'cof');

    info(p).ResourceSize = fread(fid, 1, 'uint32');
    info(p).ResourceDataOffset = fread(fid, 1, 'uint32');

    % Start reading bitmap header info
    fseek(fid, info(p).ResourceDataOffset, 'bof');
    
    info(p).BitmapHeaderSize = fread(fid, 1, 'uint32');

    fseek(fid, 8, 'cof');
    
    info(p).NumPlanes = fread(fid, 1, 'uint16');
    info(p).BitDepth = fread(fid, 1, 'uint16');
    
    fseek(fid, 4, 'cof');

    info(p).BitmapSize = fread(fid, 1, 'uint32');

    % Headers must be at least 40 bytes, but they may be larger.
    % Skip ahead to the begining of the colormap data.
    info(p).ColormapOffset = info(p).ResourceDataOffset + ...
        info(p).BitmapHeaderSize;
    
    fseek(fid, info(p).ColormapOffset, 'bof');
    
    % Read the RGBQUAD colormap: [blue green red reserved]
    info(p).NumColormapEntries = info(p).NumPlanes * ...
        2^(info(p).BitDepth);

    [data, count] = fread(fid, (info(p).NumColormapEntries)*4, 'uint8');
    
    if (count ~= info(p).NumColormapEntries*4)
        info = [];
        msg = 'Truncated colormap data';
        fclose(fid);
        return;
    end

    % Throw away the reserved byte, swap red and blue, and rescale
    data = reshape(data, 4, info(p).NumColormapEntries)';
    cmap = data(:,1:3);
    cmap = fliplr(cmap);
    cmap = cmap ./ 255;
    
    info(p).Colormap = cmap;

    info(p).ColorType = 'indexed';
    info(p).CompressionType = 'none';
    info(p).ImageDataOffset = ftell(fid);
    
    %
    % Other validity checks
    %
    if ((info(p).Width < 0) | (info(p).Height < 0))
        info = [];
        msg = 'Corrupt ICO file: bad image dimensions.';
        fclose(fid);
        return;
    end
end

fclose(fid);
