For example, if the value in the transparency chunk of an 8-bit image is 0.5020, all pixels in the image with the color 0.5020 can be displayed as transparent. The transparency chunk identifies which pixel values are treated as transparent. (A PNG file can only have one of these components, not both.) Transparent pixels, when they exist, are identified by one of two components: a transparency chunk or an alpha channel. A PNG file does not necessarily contain transparency data. The discussion in this section is only relevant to PNG files that contain transparent pixels. You can use imfinfo to match image order with reference number.) If you omit this argument, imread reads the first image in the file. (Note that in an HDF file the reference numbers do not necessarily correspond to the order of the images in the file. For example, if ref is 12, imread reads the image whose reference number is 12. ref is an integer value that specifies the reference number used to identify the image. = imread(.,ref) reads in one image from a multi-image HDF file. 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. In this case, all of the frames are read and returned in the order that they appear in the file.īecause of the way that GIF files are structured, all of the frames must be read when a particular frame is requested. = imread(.,'frames',idx) is the same as the syntax above except that idx can be 'all'. If idx is 1:5, imread returns only the first five frames. For example, if idx is 3, imread reads the third image in the file. idx must be an integer scalar or vector of integer values. = imread(.,idx) reads in one or more frames from a multiframe (i.e., animated) GIF file. If you have the Image Processing Toolbox, you can use the imresize function. You will probably need to scale your image. For cursor files, this mask may contain the only useful data.īy default, Microsoft Windows cursors are 32-by-32 pixels. = imread(.) returns the AND mask for the resource, which can be used to determine the transparency information. If you omit this argument, imread reads the first image in the file. idx is an integer value that specifies the order that the image appears in the file. = imread(.,idx) reads in one image from a multi-image icon or cursor file. PNM is not a file format itself it is a common name for any of the other three members of the Portable Bitmap family of image formats: Portable Bitmap (PBM), Portable Graymap (PGM) and Portable Pixel Map (PPM). Note that, for certain formats, imread may take additional parameters, described in Special Case Syntax. You can also get a list of all supported formats by using the imformats function. This table lists the possible values for fmt. The URL must include the protocol type (e.g., Formats = imread(filename) attempts to infer the format of the file from its content. The colormap values are rescaled to the range. = imread(filename, fmt ) reads the indexed image in filename into X and its associated colormap into map. See Formats for a list of all the possible values for fmt. If imread cannot find a file named filename, it looks for a file named filename. If the file is not in the current directory or in a directory in the MATLAB path, specify the full pathname of the location on your system. If the file contains a truecolor (RGB) image, A is a three-dimensional ( m-by- n-by-3) array.įilename is a string that specifies the name of the graphics file, and fmt is a string that specifies the format of the file. If the file contains a grayscale intensity image, A is a two-dimensional array. See Special Case Syntax for information about these syntaxes.Ī = imread(filename, fmt ) reads a grayscale or truecolor image named filename into A. The imread function also supports several other format-specific syntaxes. The imread function supports four general syntaxes, described below. = imread(.,'BackgroundColor',BG) ( PNG only) = imread(.,idx) ( CUR, ICO, and TIFF only) Imread (MATLAB Functions) MATLAB Function Reference
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