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 the image in the specified graphics file. The format of the file is inferred from its contents.

If filename is a CUR, GIF, HDF4, ICO, PBM, PGM, PPM, SVS, or TIFF 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 the function cannot find a file named filename.

Examples

Return Information About Graphics File

Find information about a sample image.

info = imfinfo("ngc6543a.jpg");

The info structure includes these fields: Filename, FileModDate, FileSize, Format, FormatVersion, Width, Height, BitDepth, ColorType, FormatSignature, NumberOfSamples, CodingMethod, CodingProcess, Comment, AutoOrientedWidth, and AutoOrientedHeight.

To display specific information from the structure, refer to its fields. For example, display the coding method information from the structure.

info.CodingMethod

ans = 
'Huffman'

Input Arguments

filename — Name of graphics file

string scalar | character vector

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

Depending on the location of your file, filename can take 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.png" Example: "\imgDir\myImage.bmp"
Uniform resource locator (URL)	If the file is located by an internet URL, then filename must contain the protocol type, such as http://. Example: "http://my_hostname/my_path/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 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://my_bucket/my_path/my_image.jpg"

fmt — Image format

string scalar | character vector

Image format, specified as a string scalar or character vector indicating the standard file extension. Call imformats to see a list of supported formats and their file extensions.

Example: "png"

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 file and the format of the file. This table describes the fields that are always included.

Field Name	Description	Value
Filename	Name of the file. If the file is not in the current folder or is in a remote location, Filename contains the full path or address 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, in the form of a file extension. For formats with more than one possible extension (for example, JPEG and TIFF), the imfinfo function returns the first variant in the file format registry. (For more information, see imformats.)	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. Possible values for ColorType include, but are not limited to, 'truecolor' for a truecolor (RGB) image, 'grayscale' for a grayscale intensity image, and 'indexed' for an indexed image.	character vector
AutoOrientedWidth (since R2024b)	Width of the image after applying the exchangeable image file format (Exif) Orientation tag, in pixels. If the file does not have an Exif Orientation tag, then this field has the same value as the Width field does.	integer
AutoOrientedHeight (since R2024b)	Height of the image after applying the Exif Orientation tag, in pixels. If the file does not have an Exif Orientation tag, then this field has the same value as the Height field does.	integer

The info structure array includes additional fields for some file formats:

• DNG only — The imfinfo function 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.

• DNG, JPEG, and TIFF only — If filename contains Exif tags, then info might include DigitalCamera or GPSInfo (global positioning system information) fields.

• GIF only — The info structure includes a DelayTime field that contains a value in hundredths of seconds.

• JPEG only

  • If filename contains embedded Extensible Metadata Platform (XMP) metadata, then info includes 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.

  • If filename contains an Exif Orientation tag, then info includes an Orientation field that contains the value of the Exif Orientation tag.

• JPEG 2000 only — The info structure includes a ChannelDefinition field that contains an m-by-3 cell array, where m is the number of rows of image data.

  • The first column of ChannelDefinition reports a channel position as it exists in the file.

  • The second column of ChannelDefinition reports the type of channel.

  • The third column of ChannelDefinition reports the channel mapping.

• TIFF only — The info structure includes an Orientation field that contains the value of the Exif Orientation tag (or contains the value 1 if there is no Exif Orientation tag).

Tips

• For JPEG and TIFF files, the info structure can include an Orientation field that contains the value of the Exif Orientation tag from the image file.

  This table shows how the imread function uses the value of the Exif Orientation tag to transform the image data when the AutoOrient name-value argument is true.

  Value of Orientation Field	Description of Transformation
  1	No transformation
  2	Reflect about vertical axis
  3	Rotate 180°
  4	Reflect about vertical axis and then rotate 180°
  5	Reflect about vertical axis and then rotate 90° counterclockwise
  6	Rotate 90° clockwise
  7	Reflect about vertical axis and then rotate 90° clockwise
  8	Rotate 90° counterclockwise

  (since R2024b)

• For Adobe DNG files, the imfinfo function returns the image dimensions of the preview image in the Height and Width fields of the info structure.

• For BMP files, the info structure 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

R2024b: Get information about automatically oriented images

The info structure includes AutoOrientedWidth and AutoOrientedHeight fields.

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.