imfinfo

Information about graphics file

Syntax

info = imfinfo(filename)

info = imfinfo(filename,fmt)

Description

info = imfinfo(filename) returns a structure whose fields contain information about an image in a graphics file, filename.

The format of the file is inferred from its contents.

• If filename is a TIFF, PGM, PBM, PPM, HDF, ICO, GIF, SVS, or CUR file containing more than one image, then info is a structure array with one element for each image in the file. For example, info(3) would contain information about the third image in the file.

info = imfinfo(filename,fmt) additionally looks for a file named filename.fmt, if MATLAB^® cannot find a file named filename.

Examples

Return Information About Graphics File

Find information about the example image, ngc6543a.jpg.

info = imfinfo('ngc6543a.jpg');

The info structure contains the following information fields: Filename, FileModDate, FileSize, Format, FormatVersion, Width, Height, BitDepth, ColorType, FormatSignature, NumberOfSamples, CodingMethod, CodingProcess, and Comment.

To display information from the structure, for example CodingMethod, type info.CodingMethod in the command window.

info.CodingMethod

ans = 
'Huffman'

To display all the properties in the structure, type info in the command window.

Input Arguments

filename — Name of graphics file

character vector | string scalar

Name of graphics file, specified as a character vector or string scalar.

Depending on the location of the file, filename can take on one of these forms.

Location	Form
Current folder or folder on the MATLAB path	Specify the name of the file in filename. Example: 'myImage.jpg'
File in a folder	If the file is not in the current folder or in a folder on the MATLAB path, then specify the full or relative path name. Example: 'C:\myFolder\myImage.ext' Example: '\imgDir\myImage.ext'
URL	If the file is located by an internet URL, then filename must contain the protocol type such as, http://. Example: 'http://hostname/path_to_file/my_image.jpg'
Remote Location	If the file is stored at a remote location, then filename must contain the full path of the file specified as a uniform resource locator (URL) of the form: scheme_name://path_to_file/my_file.ext Based on the remote location, scheme_name can be one of the values in this table. Remote Location scheme_name Amazon S3™ s3 Windows Azure® Blob Storage wasb, wasbs HDFS™ hdfs For more information, see Work with Remote Data. Example: 's3://bucketname/path_to_file/my_image.jpg'

Data Types: char | string

fmt — Image format

character vector | string scalar

Image format, specified as a character vector or string scalar. The possible values for fmt are contained in the MATLAB file format registry. To view of list of these formats, run the imformats command.

Example: 'gif'

Data Types: char | string

Output Arguments

info — Information about graphics file

structure array

Information about the graphics file, returned as a structure array. The set of fields in info depends on the individual file and its format. This table describes the nine fields that are always included.

Field Name	Description	Value
Filename	Name of the file or the internet URL specified. If the file is not in the current folder, the character vector contains the full path name of the file.	character vector
FileModDate	Date when the file was last modified.	character vector
FileSize	Size of the file, in bytes.	integer
Format	File format, as specified by fmt. For formats with more than one possible extension (for example, JPEG and TIFF files), imfinfo returns the first variant in the file format registry.	character vector
FormatVersion	File format version.	character vector or number
Width	Image width, in pixels.	integer
Height	Image height, in pixels. (For additional details about BMP files, see Tips.)	integer
BitDepth	Number of bits per pixel.	integer
ColorType	Image type. ColorType includes, but is not limited to, 'truecolor' for a truecolor (RGB) image, 'grayscale' for a grayscale intensity image, or 'indexed' for an indexed image.	character vector

Additional fields are included for some file formats:

• JPEG, DNG, and TIFF only — If filename contains Exchangeable Image File Format (EXIF) tags, then info might contain 'DigitalCamera' or 'GPSInfo' (global positioning system information) fields.

• JPEG only — If filename contains embedded Extensible Metadata Platform (XMP) metadata, then info contains an 'XMPData' field. If the XMP metadata of filename contains International Press Telecommunications Council (IPTC) data, this data is located in the 'Iptc4xmpCore' (core metadata) and 'Iptc4xmpExt' (extension metadata) subfields of the 'XMPData' field.

• GIF only — imfinfo returns the value of the 'DelayTime' field in hundredths of seconds.

• JPEG2000 only — The info structure contains an m-by-3 cell array, 'ChannelDefinition'. The first column of 'ChannelDefinition' reports a channel position as it exists in the file. The second column reports the type of channel, and the third column reports the channel mapping.

• DNG only — imfinfo returns tags belonging to Adobe^® DNG file versions up to and including 1.5 as individual named fields in the output structure. For a complete list of DNG file tags, see Chapter 4 of the Adobe Digital Negative (DNG) Specification.

Tips

• When you use imfinfo to get information about an Adobe DNG file, it returns the image dimensions of the preview image in the 'Height' and 'Width' fields of the info structure.

• When you use imfinfo to get information about a BMP file, it returns an info structure that can contain a negative 'Height' value. The negative value indicates that the origin of the image is in its upper-left corner. In such cases, the actual height of the image in pixels is the absolute value of the 'Height' value.

Version History

Introduced before R2006a

R2023a: Get information about Extensible Metadata Platform (XMP) metadata embedded in JPEG files

The imfinfo function returns XMP metadata embedded in JPEG files in the 'XMPData' field of the output structure. The function also returns International Press Telecommunications Council (IPTC) metadata embedded in the XMP namespace. The IPTC data is stored in the 'Iptc4xmpCore' (core metadata) and 'Iptc4xmpExt' (extension metadata) subfields of 'XMPData'.

R2021a: Get information about Adobe Digital Negative (DNG) tags

The imfinfo function returns information on DNG file tags belonging to versions up to and including 1.5 as individual named fields in the output structure. Previously, information on DNG file tags belonging to versions 1.2 through 1.5 was stored in the 'UnknownTags' field of the output structure.

R2019b: Output includes information on multiple images from PGM, PBM, and PPM files

If a PGM, PBM, or PPM file has multiple images, then imfinfo now returns a structure array containing information on those multiple images. Previously, imfinfo returned a 1-by-1 structure containing information about only the first image.