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>> type imread

function [X, map, alpha] = imread(varargin)

%IMREAD Read image from graphics file.

% A = IMREAD(FILENAME,FMT) reads a grayscale or color image from the file

% specified by the string FILENAME. If the file is not in the current

% directory, or in a directory on the MATLAB path, specify the full

% pathname.

%

% The text string FMT specifies the format of the file by its standard

% file extension. For example, specify ¡®gif¡¯ for Graphics Interchange

% Format files. To see a list of supported formats, with their file

% extensions, use the IMFORMATS function. If IMREAD cannot find a file

% named FILENAME, it looks for a file named FILENAME.FMT.

%

% The return value A is an array containing the image data. If the file

% contains a grayscale image, A is an M-by-N array. If the file contains

% a truecolor image, A is an M-by-N-by-3 array. For TIFF files containing

% color images that use the CMYK color space, A is an M-by-N-by-4 array.

% See TIFF in the Format-Specific Information section for more

% information.

%

% The class of A depends on the bits-per-sample of the image data,

% rounded to the next byte boundary. For example, IMREAD returns 24-bit

% color data as an array of uint8 data because the sample size for each

% color component is 8 bits. See the Remarks section for a discussion of

% bitdepths, and see the Format-Specific Information section for more

% detail about supported bitdepths and sample sizes for a particular

% format.

%

% [X,MAP] = IMREAD(FILENAME,FMT) reads the indexed image in FILENAME into

% X and its associated colormap into MAP. Colormap values in the image

% file are automatically rescaled into the range [0,1].

%

% [¡­] = IMREAD(FILENAME) attempts to infer the format of the file

% from its content.

%

% [¡­] = IMREAD(URL,¡­) reads the image from an Internet URL.

%

% Remarks

%

% Bitdepth is the number of bits used to represent each image pixel.

% Bitdepth is calculated by multiplying the bits-per-sample with the

% samples-per-pixel. Thus, a format that uses 8-bits for each color

% component (or sample) and three samples per pixel has a bitdepth of 24.

% Sometimes the sample size associated with a bitdepth can be ambiguous:

% does a 48-bit bitdepth represent six 8-bit samples or three 16-bit

% samples? The following format-specific sections provide sample size

% information to avoid this ambiguity.

%

% Format-Specific Information (Listed Alphabetically by Format)

%

% BMP ¡ª Windows Bitmap

%

% Supported Compression Output

% Bitdepths None RLE Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª

% 1-bit x ¨C logical

% 4-bit x x uint8

% 8-bit x x uint8

% 16-bit x ¨C uint8 1 sample/pixel

% 24-bit x ¨C uint8 3 samples/pixel

% 32-bit x ¨C uint8 3 samples/pixel (1 byte padding)

%

% CUR ¡ª Cursor File

%

% Supported Compression Output

% Bitdepths None Compressed Class

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C

% 1-bit x ¨C logical

% 4-bit x ¨C uint8

% 8-bit x ¨C uint8

%

% Special syntaxes:

%

% [¡­] = IMREAD(¡­,IDX) reads in one image from a multi-image icon or

% cursor file. IDX is an integer value that specifies the order that the

% image appears in the file. For example, if IDX is 3, IMREAD reads the

% third image in the file. If you omit this argument, IMREAD reads the

% first image in the file.

%

% [A,MAP,ALPHA] = IMREAD(¡­) returns the AND mask for the resource,

% which can be used to determine transparency information. For cursor

% files, this mask may contain the only useful data.

%

% GIF ¡ª Graphics Interchange Format

%

% Supported Compression Output

% Bitdepths None Compressed Class

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª

% 1-bit x ¨C logical

% 2-to-8 bit x ¨C uint8

%

% Special syntaxes:

%

% [¡­] = IMREAD(¡­,IDX) reads in one or more frames from a multiframe

% (i.e., animated) GIF file. IDX must be an integer scalar or vector of

% integer values. For example, if IDX is 3, IMREAD reads the third image

% in the file. If IDX is 1:5, only the first five frames are returned.

%

% [¡­] = IMREAD(¡­,¡¯Frames¡¯,IDX) is the same as the syntax above except

% that IDX can be ¡®all¡¯. In this case, all of the frames are read and

% returned in the order that they appear in the file.

%

% Note: Because of the way GIF files are structured, all of the frames

% must be read when a particular frame is requested. Consequently, it is

% much faster to specify a vector of frames or ¡®all¡¯ for IDX than to call

% IMREAD in a loop when reading multiple frames from the same GIF file.

%

% HDF ¡ª Hierarchical Data Format

%

% Supported Raster image Raster image Output

% Bitdepths with colormap without colormap Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª

% 8-bit x x uint8

% 24-bit ¨C x uint8 3 samples/pixel

%

% Special Syntaxes:

%

% [¡­] = IMREAD(¡­,REF) reads in one image from a multi-image HDF file.

% REF is an integer value that specifies the reference number used to

% identify the image. For example, if REF is 12, IMREAD reads the image

% whose reference number is 12. (Note that in an HDF file the reference

% numbers do not necessarily correspond with the order of the images in

% the file. You can use IMFINFO to match up image order with reference

% number.) If you omit this argument, IMREAD reads the first image in

% the file.

%

% ICO ¡ª Icon File

%

% See CUR.

%

% JPEG ¡ª Joint Photographic Experts Group

%

% Note: IMREAD can read any baseline JPEG image as well as JPEG images

% with some commonly used extensions.

%

% Supported Compression Output

% Bitdepths Lossy Lossless Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C

% 8-bit x x uint8 Grayscale or RGB

% 12-bit x x uint16 Grayscale

% 16-bit ¨C x uint16 Grayscale

% 36-bit x x uint16 RGB(Three 12-bit samples/pixel)

%

% JPEG 2000 ¨C Joint Photographic Experts Group 2000

%

% Supported Compression Output

% Bitdepths Lossy Lossless Class

% (per sample)

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª-

% 1-bit x x logical

% 2- to 8-bit x x uint8

% 9- to 16-bit x x uint16

%

% Note: Indexed JPEG 2000 images are not supported. Only JP2 compatible

% color spaces are supported for JP2/JPX files. Arbitrary channels are

% supported for raw codestream J2C files.

%

% Special Syntaxes

%

% [¡­] = IMREAD(¡­, ¡®Param1¡¯, value1, ¡®Param2¡¯, value2, ¡­) uses

% parameter-value pairs to control the read operation.

%

% Parameter name Value

% ¡ª¡ª¡ª¡ª¨C ¡ª¨C

% ¡®ReductionLevel¡¯ A non-negative integer specifying reduction in

% the resolution of the image. For a reduction

% level ¡®L¡¯, the image resolution is reduced by a

% factor of 2^L. Its default value is 0 implying

% no reduction. The reduction level is limited by

% the total number of decomposition levels as

% provided by ¡®WaveletDecompositionLevels¡¯ field

% in the structure returned from IMFINFO function.

%

% ¡®PixelRegion¡¯ {ROWS, COLS}. IMREAD returns the sub-image

% specified by the boundaries in ROWS and COLS.

% ROWS and COLS must both be two-element vectors

% that denote the 1-based indices [START STOP]. If

% ¡®ReductionLevel¡¯ is greater than 0, then ROWS and

% COLS are coordinates in the reduced-sized image.

%

% ¡®V79Compatible¡¯ A BOOL value. If true, image returned is color

% converted to gray-scale or RGB image as consistent

% with previous versions of IMREAD (MATLAB 7.9

% [R2009b] and earlier). Otherwise raw color

% image is returned. Default is false.

%

%

% PBM ¡ª Portable Bitmap

%

% Supported Raw ASCII (Plain) Output

% Bitdepths Binary Encoded Class

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª-

% 1-bit x x logical

%

% PCX ¡ª Windows Paintbrush

%

% Supported Output

% Bitdepths Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª-

% 1-bit logical Grayscale only

% 8-bit uint8 Grayscale or indexed

% 24-bit uint8 RGB (8-bit samples)

%

% PGM ¡ª Portable Graymap

%

% Supported Raw ASCII (Plain) Output

% Bitdepths Binary Encoded Class

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª

% up to 16-bit x ¨C uint8

% Arbitrary ¨C x

%

% PNG ¡ª Portable Network Graphics

%

% Supported Output

% Bitdepths Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª-

% 1-bit logical Grayscale only

% 2-bit uint8 Grayscale only

% 4-bit uint8 Grayscale only

% 8-bit uint8 Grayscale or Indexed

% 16-bit uint16 Grayscale or Indexed

% 24-bit uint8 RGB (Three 8-bit samples/pixel)

% 48-bit uint16 RGB (Three 16-bit samples/pixel)

%

% Special Syntaxes:

%

% [¡­] = IMREAD(¡­,¡¯BackgroundColor¡¯,BG) composites any transparent

% pixels in the input image against the color specified in BG. If BG is

% ¡®none¡¯, then no compositing is performed. Otherwise, if the input image

% is indexed, BG should be an integer in the range [1,P] where P is the

% colormap length. If the input image is grayscale, BG should be an

% integer in the range [0,1]. If the input image is RGB, BG should be a

% three-element vector whose values are in the range [0,1]. The string

% ¡®BackgroundColor¡¯ may be abbreviated.

%

% If the ALPHA output argument is used (see below), then BG defaults to

% ¡®none¡¯ if not specified by the user. Otherwise, if the PNG file

% ontains a background color chunk, that color is used as the default

% value for BG. If ALPHA is not used and the file does not contain a

% background color chunk, then the default value for BG is 1 for indexed

% images; 0 for grayscale images; and [0 0 0] for RGB images.

%

% [A,MAP,ALPHA] = IMREAD(¡­) returns the alpha channel if one is

% present; otherwise ALPHA is []. If ¡®BackgroundColor¡¯ is specified by

% the user then ALPHA is []. Note that MAP may be empty if the file

% contains a grayscale or truecolor image.

%

% PPM ¡ª Portable Pixmap

%

% Supported Raw ASCII (Plain) Output

% Bitdepths Binary Encoded Class

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª

% up to 16-bit x ¨C uint8

% Arbitrary ¨C x

%

% RAS ¡ª Sun Raster

%

% Supported Output

% Bitdepths Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª-

% 1-bit logical Bitmap

% 8-bit uint8 Indexed

% 24-bit uint8 RGB (8-bit samples)

% 32-bit uint8 RGB with Alpha (8-bit samples)

%

% TIFF ¡ª Tagged Image File Format

%

% Supported Compression Output

% Bitdepths None Packbits CCITT RGB ICCLAB CIELAB CMYK Class Notes

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C

% 1-bit x x x ¨C ¨C ¨C ¨C logical

% 8-bit x x ¨C ¨C ¨C ¨C ¨C uint8

% 12-bit ¨C ¨C ¨C ¨C ¨C ¨C ¨C uint16 Grayscale

% or Indexed

% 16-bit ¨C ¨C ¨C ¨C ¨C ¨C ¨C uint16 Grayscale

% or Indexed

% 24-bit x x ¨C x x x ¨C uint8 3 samples

% 32-bit ¨C ¨C ¨C ¨C ¨C ¨C x uint8 4 samples

% 36-bit ¨C ¨C ¨C x ¨C ¨C ¨C uint16 3 samples

% 48-bit ¨C ¨C ¨C x x x ¨C uint16 3 samples

% 64-bit ¨C ¨C ¨C ¨C ¨C ¨C x double 4 samples

%

% NOTE: IMREAD supports 8-bit integral and 32-bit floating point tiled

% TIFF images, with any compression and colorspace combination listed

% above, and 32-bit IEEE floating point images.

%

% Special Syntaxes:

%

% A = IMREAD(¡­) returns color data that uses the RGB, CIELAB, ICCLAB,

% or CMYK color spaces. If the color image uses the CMYK color space, A

% is an M-by-N-by-4 array.

%

% [¡­] = IMREAD(¡­, ¡®Param1¡¯, value1, ¡®Param2¡¯, value2, ¡­) uses

% parameter-value pairs to control the read operation. There are three

% different parameters you can use:

%

% Parameter name Value

% ¡ª¡ª¡ª¡ª¨C ¡ª¨C

% ¡®Index¡¯ A positive integer specifying which image to read in

% a multi-image TIFF file. For example, if ¡®Index¡¯ is

% 3, IMREAD reads the third image in the file.

%

% ¡®Info¡¯ A structure array; the output of IMFINFO. When

% reading images from a multi-image TIFF file, passing

% the output of IMFINFO as the ¡®Info¡¯ parameter helps

% IMREAD locate the images in the file more quickly.

%

% ¡®PixelRegion¡¯ {ROWS, COLS}. IMREAD returns the sub-image

% specified by the boundaries in ROWS and COLS. ROWS

% and COLS must be either two- or three-element

% vectors. If two elements are provided, they denote

% the 1-based indices [START STOP]. If three elements

% are provided, the indices [START INCREMENT STOP]

% allow image downsampling.

%

% XWD ¡ª X Window Dump

%

% Supported Output

% Bitdepths ZPixmaps XYBitmaps XYPixmaps Class

% ¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C

% 1-bit x ¨C x logical

% 8-bit x ¨C ¨C uint8

%

% Please read the file libtiffcopyright.txt for more information.

%

% Example:

%

% imdata = imread(¡®ngc6543a.jpg¡¯);

%

% See also IMFINFO, IMWRITE, IMFORMATS, FREAD, IMAGE, DOUBLE, UINT8.

% Copyright 1984-2011 The MathWorks, Inc.

% Revision: 1.1.6.22.4.1 Date: 2012/07/02 18:58:54

[filename, fmt_s, extraArgs] = parse_inputs(varargin{:});

% Download remote file.

if (strfind(filename, ¡®://¡¯))

url = true;

if (~usejava(¡®jvm¡¯))

error(message(¡®MATLAB:imagesci:imread:noJava¡¯))

end

try

filename = urlwrite(filename, tempname);

catch %#ok

error(message(¡®MATLAB:imagesci:imread:readURL¡¯, filename));

end

else

url = false;

end

if (isempty(fmt_s))

% The format was not specified explicitly.

% Verify that the file exists.

fid = fopen(filename, ¡®r¡¯);

if (fid == -1)

if ~isempty(dir(filename))

error(message(¡®MATLAB:imagesci:imread:fileReadPermission¡¯, filename));

else

error(message(¡®MATLAB:imagesci:imread:fileDoesNotExist¡¯, filename));

end

else

% File exists. Get full filename.

filename = fopen(fid);

fclose(fid);

end

% Try to determine the file type.

[format, fmt_s] = imftype(filename);

if (isempty(format))

error(message(¡®MATLAB:imagesci:imread:fileFormat¡¯));

end

else

% The format was specified explicitly.

% Verify that the file exists.

fid = fopen(filename, ¡®r¡¯);

if (fid == -1)

% Couldn¡¯t open using the given filename; search for a

% file with an appropriate extension.

for p = 1:length(fmt_s.ext)

fid = fopen([filename ¡®.¡¯ fmt_s.ext{p}]);

if (fid ~= -1)

% The file was found. Don¡¯t continue searching.

break

end

end

end

if (fid == -1)

if ~isempty(dir(filename))

error(message(¡®MATLAB:imagesci:imread:fileReadPermission¡¯, filename));

else

error(message(¡®MATLAB:imagesci:imread:fileDoesNotExist¡¯, filename));

end

else

filename = fopen(fid);

fclose(fid);

end

end

if isempty(fmt_s)

% Get format details.

fmt_s = imformats(format);

end

% Verify that a read function exists

if (isempty(fmt_s.read))

error(message(¡®MATLAB:imagesci:imread:readFunctionRegistration¡¯, fmt_s.ext{ 1 }));

end

if ((fmt_s.alpha) && (nargout == 3))

% Use the alpha channel.

[X, map, alpha] = feval(fmt_s.read, filename, extraArgs{:});

else

% Alpha channel is not requested or is not applicable.

alpha = [];

[X, map] = feval(fmt_s.read, filename, extraArgs{:});

end

% Delete temporary file from Internet download.

if (url)

delete_download(filename);

end

%¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C

function delete_download(filename)

try

delete(filename);

catch

warning(message(¡®MATLAB:imagesci:imread:tempFileDelete¡¯, filename))

end

%¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¡ª¨C

function [filename, fmt_s, extraArgs] = parse_inputs(varargin)

filename = ¡±;

fmt_s = struct([]);

extraArgs = {};

% Parse arguments based on their number.

switch(nargin)

case 0

% Not allowed.

error(message(¡®MATLAB:imagesci:imread:inputParsing¡¯));

case 1

% Filename only.

filename = varargin{1};

if ~ischar(filename)

error(message(¡®MATLAB:imagesci:imread:badImageSourceDatatype¡¯));

end

otherwise

% Filename and format or other arguments.

filename = varargin{1};

% Check whether second argument is a format.

if (ischar(varargin{2}))

fmt_s = imformats(varargin{2});

end

if (~isempty(fmt_s))

% The argument matches a format.

extraArgs = varargin(3:end);

else

% The argument begins the format-specific parameters.

extraArgs = varargin(2:end);

end

end

>>

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