Exporting to Images

To export data from the MATLAB^® workspace using one of the standard graphics file formats, use the imwrite function. Using this function, you can export data in formats such as the Tagged Image File Format (TIFF), Joint Photographic Experts Group (JPEG), and Portable Network Graphics (PNG). For a complete list of supported formats, see the imwrite reference page.

The following example writes a multidimensional array of uint8 data I from the MATLAB workspace into a file in TIFF format. The class of the output image written to the file depends on the format specified. For most formats, if the input array is of class uint8, imwrite outputs the data as 8-bit values. See the imwrite reference page for details.

whos I
  Name      Size                           Bytes  Class

  I       650x600x3                      1170000  uint8 array

Grand total is 1170000 elements using 1170000 bytes
imwrite(I, 'my_graphics_file.tif','tif');

Note

imwrite supports different syntaxes for several of the standard formats. For example, with TIFF file format, you can specify the type of compression MATLAB uses to store the image. See the imwrite reference page for details.

For more control writing data to a TIFF file, use the Tiff object—see Exporting Image Data and Metadata to TIFF Files for more information.

Exporting Image Data and Metadata to TIFF Files

While you can use imwrite to export image data and metadata (tags) to Tagged Image File Format (TIFF) files, the function does have some limitations. For example, when you want to modify image data or metadata in the file, you must write the all the data to the file. You cannot write only the updated portion. Using the Tiff object, you can write portions of the image data and modify or add individual tags to a TIFF file. When you construct a Tiff object, it represents your connection with a TIFF file and provides access to many of the routines in the LibTIFF library.

The following sections provide step-by-step examples of using Tiff object methods and properties to perform some common tasks with TIFF files. To get the most out of the Tiff object, you must be familiar with the TIFF specification and technical notes. View this documentation at LibTIFF - TIFF Library and Utilities.

Creating a New TIFF File

Create some image data. This example reads image data from a JPEG file included with MATLAB:
```
imgdata = imread('ngc6543a.jpg');
```
Create a new TIFF file by constructing a Tiff object, specifying the name of the new file as an argument. To create a file you must specify either write mode ('w') or append mode ('a'):
```
t = Tiff('myfile.tif','w');
```
When you create a new TIFF file, the Tiff constructor creates a file containing an image file directory (IFD). A TIFF file uses this IFD to organize all the data and metadata associated with a particular image. A TIFF file can contain multiple IFDs. The Tiff object makes the IFD it creates the current IFD. Tiff object methods operate on the current IFD. You can navigate among IFDs in a TIFF file and specify which IFD is the current IFD using Tiff object methods.
Set required TIFF tags using the setTag method of the Tiff object. These required tags specify information about the image, such as its length and width. To break the image data into strips, specify a value for the RowsPerStrip tag. To break the image data into tiles, specify values for the TileWidth and TileLength tags. The example creates a structure that contains tag names and values and passes that to setTag. You also can set each tag individually.
```
tagstruct.ImageLength = size(imgdata,1);
tagstruct.ImageWidth = size(imgdata,2);
tagstruct.Photometric = Tiff.Photometric.RGB;
tagstruct.BitsPerSample = 8;
tagstruct.SamplesPerPixel = 3;
tagstruct.RowsPerStrip = 16;
tagstruct.PlanarConfiguration = Tiff.PlanarConfiguration.Chunky;
tagstruct.Software = 'MATLAB';
tagstruct % display tagstruct
setTag(t,tagstruct)
```
For information about supported TIFF tags and how to set their values, see Setting Tag Values. For example, the Tiff object supports properties that you can use to set the values of certain properties. This example uses the Tiff object PlanarConfiguration property to specify the correct value for the chunky configuration: Tiff.PlanarConfiguration.Chunky.
Write the image data and metadata to the current directory using the write method of the Tiff object.
```
write(t,imgdata);
```
If you wanted to put multiple images into your file, call the writeDirectory method right after performing this write operation. The writeDirectory method sets up a new image file directory in the file and makes this new directory the current directory.
Close your connection to the file by closing the Tiff object:
```
close(t);
```
Test that you created a valid TIFF file by using the imread function to read the file, and then display the image:
```
imagesc(imread('myfile.tif'));
```

Writing a Strip or Tile of Image Data

Note

You can only modify a strip or a tile of image data if the data is not compressed.

Open an existing TIFF file for modification by creating a Tiff object. This example uses the file created in Creating a New TIFF File. The Tiff constructor returns a handle to a Tiff object.
```
t = Tiff('myfile.tif','r+');
```
Generate some data to write to a strip in the image. This example creates a three-dimensional array of zeros that is the size of a strip. The code uses the number of rows in a strip, the width of the image, and the number of samples per pixel as dimensions. The array is an array of uint8 values.
```
width = getTag(t,'ImageWidth');
height = getTag(t,'RowsPerStrip');
numSamples = getTag(t,'SamplesPerPixel');
stripData = zeros(height,width,numSamples,'uint8');
```
If the image data had a tiled layout, you would use the TileWidth and TileLength tags to specify the dimensions.
Write the data to a strip in the file using the writeEncodedStrip method. Specify the index number that identifies the strip you want to modify. The example picks strip 18 because it is easier to see the change in the image.
```
writeEncodedStrip(t,18,stripData);
```
If the image had a tiled layout, you would use the writeEncodedTile method to modify the tile.
Close your connection to the file by closing the Tiff object.
```
close(t);
```
Test that you modified a strip of the image in the TIFF file by using the imread function to read the file, and then display the image.
```
modified_imgdata = imread('myfile.tif');
imagesc(modified_imgdata)
```
Note the black strip across the middle of the image.

Modifying TIFF File Metadata (Tags)

Open an existing TIFF file for modification using the Tiff object. This example uses the file created in Creating a New TIFF File. The Tiff constructor returns a handle to a Tiff object.
```
t = Tiff('myfile.tif','r+');
```
Verify that the file does not contain the Artist tag, using the getTag method. This code should issue an error message saying that it was unable to retrieve the tag.
```
artist_value = getTag(t,'Artist');
```
Add the Artist tag using the setTag method.
```
setTag(t,'Artist','Pablo Picasso');
```
Write the new tag data to the TIFF file using the rewriteDirectory method. Use the rewriteDirectory method when modifying existing metadata in a file or adding new metadata to a file.
```
rewriteDirectory(t);
```
Close your connection to the file by closing the Tiff object.
```
close(t);
```
Test your work by reopening the TIFF file and getting the value of the Artist tag, using the getTag method.
```
t = Tiff('myfile.tif', 'r');

getTag(t,'Artist')

ans =

Pablo Picasso

close(t);
```

Creating TIFF File Subdirectories

Create some image data. This example reads image data from a JPEG file included with MATLAB. The example then creates two reduced-resolution (thumbnail) versions of the image data.
```
imgdata = imread('ngc6543a.jpg');
%
% Reduce number of pixels by a half.
img_half = imgdata(1:2:end,1:2:end,:);
%
% Reduce number of pixels by a third.
img_third = imgdata(1:3:end,1:3:end,:);
```
Create a new TIFF file by constructing a Tiff object and specifying the name of the new file as an argument. To create a file you must specify either write mode ('w') or append mode ('a'). The Tiff constructor returns a handle to a Tiff object.
```
t = Tiff('my_subimage_file.tif','w');
```
Set required TIFF tags using the setTag method of the Tiff object. These required tags specify information about the image, such as its length and width. To break the image data into strips, specify a value for the RowsPerStrip tag. To break the image data into tiles, use the TileWidth and TileLength tags. The example creates a structure that contains tag names and values and passes that to setTag. You can also set each tag individually.
To create subdirectories, you must set the SubIFD tag, specifying the number of subdirectories you want to create. Note that the number you specify isn't the value of the SubIFD tag. The number tells the Tiff software to create a SubIFD that points to two subdirectories. The actual value of the SubIFD tag will be the byte offsets of the two subdirectories.
```
tagstruct.ImageLength = size(imgdata,1);
tagstruct.ImageWidth = size(imgdata,2);
tagstruct.Photometric = Tiff.Photometric.RGB;
tagstruct.BitsPerSample = 8;
tagstruct.SamplesPerPixel = 3;
tagstruct.RowsPerStrip = 16;
tagstruct.PlanarConfiguration = Tiff.PlanarConfiguration.Chunky;
tagstruct.Software = 'MATLAB';
tagstruct.SubIFD = 2 ;  % required to create subdirectories
tagstruct  % display tagstruct
setTag(t,tagstruct)
```
For information about supported TIFF tags and how to set their values, see Setting Tag Values. For example, the Tiff object supports properties that you can use to set the values of certain properties. This example uses the Tiff object PlanarConfiguration property to specify the correct value for the chunky configuration: Tiff.PlanarConfiguration.Chunky.
Write the image data and metadata to the current directory using the write method of the Tiff object.
```
write(t,imgdata);
```
Set up the first subdirectory by calling the writeDirectory method. The writeDirectory method sets up the subdirectory and make the new directory the current directory. Because you specified that you wanted to create two subdirectories, writeDirectory sets up a subdirectory.
```
writeDirectory(t);
```

Set required tags, just as you did for the regular directory. According to the LibTIFF API, a subdirectory cannot contain a SubIFD tag.

tagstruct2.ImageLength = size(img_half,1);
tagstruct2.ImageWidth = size(img_half,2);
tagstruct2.Photometric = Tiff.Photometric.RGB;
tagstruct2.BitsPerSample = 8;
tagstruct2.SamplesPerPixel = 3;
tagstruct2.RowsPerStrip = 16;
tagstruct2.PlanarConfiguration = Tiff.PlanarConfiguration.Chunky;
tagstruct2.Software = 'MATLAB';
tagstruct2  % display tagstruct2
setTag(t,tagstruct2)

Write the image data and metadata to the subdirectory using the write method of the Tiff object.
```
write(t,img_half);
```
Set up the second subdirectory by calling the writeDirectory method. The writeDirectory method sets up the subdirectory and makes it the current directory.
```
writeDirectory(t);
```

Set required tags, just as you would for any directory. According to the LibTIFF API, a subdirectory cannot contain a SubIFD tag.

tagstruct3.ImageLength = size(img_third,1);
tagstruct3.ImageWidth = size(img_third,2);
tagstruct3.Photometric = Tiff.Photometric.RGB;
tagstruct3.BitsPerSample = 8;
tagstruct3.SamplesPerPixel = 3;
tagstruct3.RowsPerStrip = 16;
tagstruct3.PlanarConfiguration = Tiff.PlanarConfiguration.Chunky;
tagstruct3.Software = 'MATLAB';
tagstruct3  % display tagstruct3
setTag(t,tagstruct3)

Write the image data and metadata to the subdirectory using the write method of the Tiff object:
```
write(t,img_third);
```
Close your connection to the file by closing the Tiff object:
```
close(t);
```

Setting Tag Values

The following table lists all the TIFF tags that the Tiff object supports and includes information about their MATLAB class and size. For certain tags, the table also indicates the set of values that the Tiff object supports, which is a subset of all the possible values defined by the TIFF specification. You can use the Tiff properties structure to specify the supported values for these tags. For example, use Tiff.Compression.JPEG to specify JPEG compression. See the Tiff reference page for a full list of properties.

Table 1: Supported TIFF Tags

TIFF Tag	Class	Size	Supported Values	Notes
`Artist`	`char`	`1xN`
`BitsPerSample`	`double`	`1x1`	1,8,16,32,64	See Table 2
`ColorMap`	`double`	`256x3`	Values should be normalized between 0–1. Stored internally as `uint16` values.	`Photometric` must be `Palette`
`Compression`	`double`	`1x1`	`None`: 1 `CCITTRLE`: 2 `CCITTFax3`: 3 `CCITTFax4`: 4 `LZW`: 5 `JPEG`: 7 `CCITTRLEW`: 32771 `PackBits`: 32773 `Deflate`: 32946 `AdobeDeflate`: 8	See Table 3.
`Copyright`	`char`	`1xN`
`DateTime`	`char`	`1x19`	Return value is padded to 19 chars if required.
`DocumentName`	`char`	`1xN`
`DotRange`	`double`	`1x2`		`Photometric` must be `Separated`
`ExtraSamples`	`double`	`1xN`	`Unspecified`: 0 `AssociatedAlpha`: 1 `UnassociatedAlpha`: 2	See Table 4.
`FillOrder`	`double`	`1x1`
`GeoAsciiParamsTag`	`char`	`1xN`
`GeoDoubleParamsTag`	`double`	`1xN`
`GeoKeyDirectoryTag`	`double`	`Nx4`
`Group3Options`	`double`	`1x1`		`Compression` must be `CCITTFax3`
`Group4Options`	`double`	`1x1`		`Compression` must be `CCITTFax4`
`HalfToneHints`	`double`	`1x2`
`HostComputer`	`char`	`1xn`
`ICCProfile`	`uint8`	`1xn`
`ImageDescription`	`char`	`1xn`
`ImageLength`	`double`	`1x1`
`ImageWidth`	`double`	`1x1`
`InkNames`	`char cell array`	`1x` `NumInks`		`Photometric` must be `Separated`
`InkSet`	`double`	`1x1`	`CMYK`: 1 `MultiInk`: 2	`Photometric` must be `Separated`
`JPEGQuality`	`double`	`1x1`	A value between 1 and 100
`Make`	`char`	`1xn`
`MaxSampleValue`	`double`	`1x1`	0–65,535
`MinSampleValue`	`double`	`1x1`	0–65,535
`Model`	`char`	`1xN`
`ModelPixelScaleTag`	`double`	`1x3`
`ModelTiepointTag`	`double`	`Nx6`
`ModelTransformationMatrixTag`	`double`	`1x16`
`NumberOfInks`	`double`	`1x1`		Must be equal to `SamplesPerPixel`
`Orientation`	`double`	`1x1`	`TopLeft`: 1 `TopRight`: 2 `BottomRight`: 3 `BottomLeft`: 4 `LeftTop`: 5 `RightTop`: 6 `RightBottom`: 7 `LeftBottom`: 8
`PageName`	`char`	`1xN`
`PageNumber`	`double`	`1x2`
`Photometric`	`double`	`1x1`	`MinIsWhite`: 0 `MinIsBlack`: 1 `RGB`: 2 `Palette`: 3 `Mask`: 4 `Separated`: 5 `YCbCr`: 6 `CIELab`: 8 `ICCLab`: 9 `ITULab`: 10	See Table 2.
`Photoshop`	`uint8`	`1xN`
`PlanarConfiguration`	`double`	`1x1`	`Chunky`: 1 `Separate`: 2
`PrimaryChromaticities`	`double`	`1x6`
`ReferenceBlackWhite`	`double`	`1x6`
`ResolutionUnit`	`double`	`1x1`
`RICHTIFFIPTC`	`uint8`	`1xN`
`RowsPerStrip`	`double`	`1x1`
`RPCCoefficientTag`	`double`	`1x92`	92-element row vector	See Table 6
`SampleFormat`	`double`	`1x1`	`Uint`: 1 `Int`: 2 `IEEEFP`: 3	See Table 2
`SamplesPerPixel`	`double`	`1x1`
`SMaxSampleValue`	`double`	`1x1`	Range of MATLAB data type specified for Image data
`SMinSampleValue`	`double`	`1x1`	Range of MATLAB data type specified for Image data
`Software`	`char`	`1xN`
`StripByteCounts`	`double`	`1xN`		Read-only
`StripOffsets`	`double`	`1xN`		Read-only
`SubFileType`	`double`	`1x1`	`Default` : 0 `ReducedImage`: 1 `Page`: 2 `Mask`: 4
`SubIFD`	`double`	`1x1`
`TargetPrinter`	`char`	`1xN`
`Thresholding`	`double`	`1x1`	`BiLevel`: 1 `HalfTone`: 2 `ErrorDiffuse`: 3	`Photometric` can be either: `MinIsWhite` `MinIsBlack`
`TileByteCounts`	`double`	`1xN`		Read-only
`TileLength`	`double`	`1x1`	Must be a multiple of 16
`TileOffsets`	`double`	`1xN`		Read-only
`TileWidth`	`double`	`1x1`	Must be a multiple of 16
`TransferFunction`	`double`	See note¹	Each value should be within 0–2^16-1	`SamplePerPixel` can be either 1 or 3
`WhitePoint`	`double`	`1x2`		`Photometric` can be: `RGB` `Palette` `YCbCr` `CIELab` `ICCLab` `ITULab`
`XMP`	`char`	`1xn`		`N>5`
`XPostion`	`double`	`1x1`
`XResolution`	`double`	`1x1`
`YCbCrCoefficents`	`double`	`1x3`		`Photometric` must be `YCbCr`
`YCbCrPositioning`	`double`	`1x1`	`Centered`: 1 `Cosited`: 2	`Photometric` must be `YCbCr`
`YCbCrSubSampling`	`double`	`1x2`		`Photometric` must be `YCbCr`
`YPosition`	`double`	`1x1`
`YResolution`	`double`	`1x1`
`ZipQuality`	`double`	`1x1`	Value between 1 and 9

¹Size is 1x2^BitsPerSample or3x2^BitsPerSample.

Table 2: Valid SampleFormat Values for BitsPerSample Settings

BitsPerSample	SampleFormat	MATLAB Data Type
1	`Uint`	`logical`
8	`Uint`, `Int`	`uint8`, `int8`
16	`Uint`, `Int`	`uint16`, `int16`
32	`Uint`, `Int`, `IEEEFP`	`uint32`, `int32`, `single`
64	`IEEEFP`	`double`

Table 3: Valid SampleFormat Values for BitsPerSample and Photometric Combinations

	BitsPerSample Values
Photometric Values	1	8	16	32	64
`MinIsWhite`	`Uint`	`Uint/Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`
`MinIsBlack`	`Uint`	`Uint/Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`
`RGB`		`Uint`	`Uint`	`Uint` `IEEEFP`	`IEEEFP`
`Pallette`		`Uint`	`Uint`
`Mask`	`Uint`
`Separated`		`Uint`	`Uint`	`Uint` `IEEEFP`	`IEEEFP`
`YCbCr`		`Uint`	`Uint`	`Uint` `IEEEFP`	`IEEEFP`
`CIELab`		`Uint`	`Uint`
`ICCLab`		`Uint`	`Uint`
`ITULab`		`Uint`	`Uint`

Table 4: Valid SampleFormat Values for BitsPerSample and Compression Combinations

	BitsPerSample Values
Compression Values	1	8	16	32	64
`None`	`Uint`	`Uint` `Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`
`CCITTRLE`	`Uint`
`CCITTFax3`	`Uint`
`CCITTFax4`	`Uint`
`LZW`	`Uint`	`Uint` `Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`
`JPEG`		`Uint` `Int`
`CCITTRLEW`	`Uint`
`PackBits`	`Uint`	`Uint` `Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`
`Deflate`	`Uint`	`Uint` `Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`
`AdobeDeflate`	`Uint`	`Uint` `Int`	`Uint` `Int`	`Uint` `Int` `IEEEFP`	`IEEEFP`

Table 5: Valid SamplesPerPixel Values for Photometric Settings

Photometric Values	SamplesPerPixel¹
`MinIsWhite`	`1+`
`MinIsBlack`	`1+`
`RGB`	`3+`
`Pallette`	`1`
`Mask`	`1`
`Separated`	`1+`
`YCbCr`	`3`
`CIELab`	`3+`
`ICCLab`	`3+`
`ITULab`	`3+`

Table 6: List of RPCCoefficientTag Value Descriptions

Index Value in 92-Element Vector	Value Descriptions¹	Units
1	Root mean square bias error	meters per horizontal axis
2	Root mean square random error	meters per horizontal axis
3	Line offset	pixels
4	Sample offset	pixels
5	Geodetic latitude offset	degrees
6	Geodetic longitude offset	degrees
7	Geodetic height offset	meters
8	Line scale factor	pixels
9	Sample scale factor	pixels
10	Geodetic latitude scale	degrees
11	Geodetic longitude scale	degrees
12	Geodetic height scale factor	meters
13 through 32	Numerator coefficients of r(n), a rational polynomial equation ²
33 through 52	Denominator coefficients of the rational polynomial equation r(n)
53 through 72	Numerator coefficients of c(n), a rational polynomial equation ²
73 through 92	Denominator coefficients of the rational polynomial equation c(n)

¹To specify the values in this vector using the RPCCoefficientTag object, see RPCCoefficientTag (Mapping Toolbox) in the Mapping Toolbox™.

²Equations r(n) and c(n) represent the normalized row and column values of a generic rigorous projection model.

External Websites

Importing Images