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% LANADAPTER Example ImageAdapter for Erdas LAN images.
% LANADAPTER is an example class that shows how one can use the ImageAdapter
% object-oriented interface to read and write to custom image file formats.
%
% The ImageAdapter class defines an interface that the Image Processing
% Toolbox function BLOCKPROC can use to read and write data to files on
% disk. This is useful when trying to process images that are too large
% to conveniently load into memory. Classes such as this one allow users
% to do a wide range of image processing operations on arbitrarily large
% files using BLOCKPROC.
%
% In this example we have written an ImageAdapter class that can read
% Erdas LAN format files. This class is for educational purposes ONLY.
%
% To keep the class as simple as possible, we have limited the scope of
% this class to read only LAN files containing uint8 data. Additionally,
% this class cannot be used to write new LAN files.
%
% Constructor
% -----------
% ADAPTER = LANADAPTER(FILENAME) creates a LanAdapter object, ADAPTER,
% associated with the Erdas LAN file, FILENAME. The resulting adapter
% can be used as an input data source to BLOCKPROC.
%
% Properties
% ----------
% Since Erdas LAN files can contain many different bands of imagery, we
% have opted to define an additional property:
%
% SelectedBands
%
% The SelectedBands property holds a vector of band numbers. When
% invoking the readRegion method, this property determines which bands of
% data are returned and in what order they are returned.
%
% Methods
% -------
% In order to create a custom ImageAdapter class, we must inherit from
% the super-class ImageAdapter. In doing so, we are required to
% implement the following class methods for our file format:
%
% readRegion(region_start,region_size)
% close()
%
% Examples
% --------
% In this example, we read the data from a LAN file using a LanAdapter
% object. The 7-band file, paris.lan, stores the RGB visible imagery in
% bands 3, 2, and 1. We will set the SelectedBands property to specify
% that our adapter return these bands only. Next we will use BLOCKPROC
% to read the data and write it back out as a truecolor TIFF file via the
% 'Destination' parameter.
%
% paris_adapter = LanAdapter('paris.lan');
% paris_adapter.SelectedBands = [3 2 1];
% % the block function is a no-op, simply returning the data
% copyFun = @(block_struct) block_struct.data;
% blockproc(paris_adapter,[100 100],copyFun,'Destination','paris_rgb.tif');
% imshow('paris_rgb.tif');
%
% The data in this specturm is concentrated within a small part of the
% available dynamic range. This is one reason why the truecolor
% composite appears dull. We will now change the function handle
% supplied to BLOCKPROC to do a contrast stretch instead of simply
% returning the raw data.
%
% stretchFun = @(block_struct) imadjust(block_struct.data,...
% stretchlim(block_struct.data));
% blockproc(paris_adapter,[100 100],stretchFun,'Destination','paris_rgb2.tif');
% figure;
% imshow('paris_rgb2.tif');
%
% See also BLOCKPROC, IMAGEADAPTER.
% Copyright 2009-2012 The MathWorks, Inc.
classdef LanAdapter < ImageAdapter
properties(GetAccess = public, SetAccess = private)
Filename
NumBands
end
properties(Access = public)
SelectedBands
end
methods
function obj = LanAdapter(fname)
% LanAdapter Constructor for LanAdapter class.
% When creating a new LanAdapter object we will read the file
% header to validate the file as well as save some image
% properties for later use.
% Open the file
obj.Filename = fname;
fid = fopen(fname,'r');
% Verify that the file begins with the string 'HEADER' or
% 'HEAD74', as per the Erdas LAN file specification.
header_str = fread(fid,6,'uint8=>char');
if ~(strcmp(header_str','HEADER') || strcmp(header_str','HEAD74'))
error('Invalid LAN file header.');
end
% Read the data type from the header
pack_type = fread(fid,1,'uint16',0,'ieee-le');
if ~isequal(pack_type,0)
error('Unsupported pack type. The LanAdapter example only supports reading uint8 data.');
end
% Band information
obj.NumBands = fread(fid,1,'uint16',0,'ieee-le');
% By default, we will return all bands of data
obj.SelectedBands = 1:obj.NumBands;
% Image width and height
unused_field = fread(fid,6,'uint8',0,'ieee-le'); %#ok<NASGU>
width = fread(fid,1,'uint32',0,'ieee-le');
height = fread(fid,1,'uint32',0,'ieee-le');
obj.ImageSize = [height width];
% Close the file handle
fclose(fid);
end % LanAdapter
function data = readRegion(obj, region_start, region_size)
% readRegion reads a rectangular block of data from the file.
% Prepare various arguments to MULTIBANDREAD
header_size = 128;
rows = region_start(1):(region_start(1) + region_size(1) - 1);
cols = region_start(2):(region_start(2) + region_size(2) - 1);
% Call MULTIBANDREAD read to get the data
full_size = [obj.ImageSize obj.NumBands];
data = multibandread(obj.Filename, full_size,...
'uint8=>uint8', header_size, 'bil', 'ieee-le',...
{'Row', 'Direct', rows},...
{'Column','Direct', cols},...
{'Band', 'Direct', obj.SelectedBands});
end % readRegion
function close(obj) %#ok<MANU>
% close the LanAdapter object. This method is a part of the
% ImageAdapter interface and is required. Since our readRegion
% method is "atomic", we have no open file handles to close,
% so this method is empty.
end
end % public methods
end % LanAdapter