imwrite - Write image to graphics file - MATLAB (original) (raw)

Write image to graphics file

Syntax

Description

imwrite([A](#btv3cny-1-A),[filename](#btv3cny-1-filename)) writes image data A to the file specified by filename, inferring the file format from the extension. imwrite creates the new file in your current folder. The bit depth of the output image depends on the data type ofA and the file format. For most formats:

• If A is of data type uint8, thenimwrite outputs 8-bit values.
• If A is of data type uint16 and the output file format supports 16-bit data (JPEG, PNG, and TIFF), thenimwrite outputs 16-bit values. If the output file format does not support 16-bit data, then imwrite returns an error.
• If A is a grayscale or RGB color image of data typedouble or single, thenimwrite assumes that the dynamic range is [0, 1] and automatically scales the data by 255 before writing it to the file as 8-bit values. If the data in A is single, convertA to double before writing to a GIF or TIFF file.
• If A is of data type logical, thenimwrite assumes that the data is a binary image and writes it to the file with a bit depth of 1, if the format allows it. BMP, PNG, or TIFF formats accept binary images as input arrays.

If A contains indexed image data, you should additionally specify themap input argument.

example

imwrite([A](#btv3cny-1-A),[map](#btv3cny-1-map),[filename](#btv3cny-1-filename)) writes the indexed image in A and its associated colormapmap to the file specified by filename.

• If A is an indexed image of data typedouble or single, thenimwrite converts the indices to zero-based indices by subtracting 1 from each element, and then writes the data as uint8. If the data in A is single, convertA to double before writing to a GIF or TIFF file.

example

imwrite(___,[fmt](#btv3cny-1-fmt)) writes the image in the format specified by fmt, regardless of the file extension infilename. You can specify fmt after the input arguments in any of the previous syntaxes.

imwrite(___,[Name,Value](#namevaluepairarguments)) specifies additional parameters for output GIF, HDF, JPEG, PBM, PGM, PNG, PPM, and TIFF files, using one or more name-value arguments. For example, you can add a comment to an image in PNG format.

example

Examples

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Write a 50-by-50 array of grayscale values to a PNG file in the current folder.

A = rand(50); imwrite(A,"myGray.png")

Write an indexed image array and its associated colormap to a PNG file.

Load sample image data from the file earth.mat.

The image array X and its associated colormap map are loaded into the workspace.

Write the data to a new PNG file.

imwrite(X,map,"myearth.png")

imwrite creates the file myearth.png in your current folder.

View the new PNG file using imshow.

Write image data to a new PNG file with the built-in MATLAB® colormap copper.

Load sample image data from the file earth.mat.

The image array X and its associated colormap map are loaded into the workspace. map is a matrix of 64 RGB vectors.

Create a copper-tone colormap with 64 RGB vectors. Then write the image data to a PNG file using the new colormap.

newmap = copper(64); imwrite(X,newmap,"copperearth.png");

imwrite creates the file copperearth.png in your current folder.

View the new PNG file using imshow.

imshow("copperearth.png")

Create and write truecolor image data to a JPEG file.

Create a 49-by-49-by-3 array of random RGB values.

Write the image data to a JPEG file. imwrite automatically chooses this format when you use the .jpg file extension. Add a comment to the file using the Comment name-value argument.

imwrite(A,"newImage.jpg","Comment","My JPEG file")

View information about the new file.

info = imfinfo("newImage.jpg"); info.ColorType

[info.Height,info.Width,info.NumberOfSamples,info.BitDepth]

ans = 1×1 cell array {'My JPEG file'}

Write multiple images to a single multipage TIFF file.

Create two sets of random image data, im1 and im2.

im1 = rand(50,40,3); im2 = rand(50,50,3);

Write the first image to a new TIFF file. Then, append the second image to the same file.

imwrite(im1,"myMultipageFile.tiff") imwrite(im2,"myMultipageFile.tiff","WriteMode","append")

Draw a series of plots, capture them as images, and write them into one animated GIF file.

Plot y=xn for n=3.

x = 0:0.01:1; n = 3; y = x.^n; plot(x,y,LineWidth=3) title("$y = x^n$, n=n = n=" + num2str(n),Interpreter="latex")

Capture a series of plots for increasing values of n.

n = 1:0.5:5; nImages = length(n);

fig = figure; for idx = 1:nImages y = x.^n(idx); plot(x,y,LineWidth=3) title("$y = x^n$, n=n = n=" + num2str(n(idx)),Interpreter="latex") drawnow frame = getframe(fig); im{idx} = frame2im(frame); end close;

Display the series of images in one figure.

figure; for idx = 1:nImages subplot(3,3,idx) imshow(im{idx}); end

Save the nine images into a GIF file. Because three-dimensional data is not supported for GIF files, call rgb2ind to convert the RGB data in the image to an indexed image A with a colormap map. To append multiple images to the first image, call imwrite with the name-value argument WriteMode set to "append".

filename = "testAnimated.gif"; % Specify the output file name for idx = 1:nImages [A,map] = rgb2ind(im{idx},256); if idx == 1 imwrite(A,map,filename,"gif",LoopCount=Inf, ... DelayTime=1) else imwrite(A,map,filename,"gif",WriteMode="append", ... DelayTime=1) end end

imwrite writes the GIF file to your current folder. Setting LoopCount to Inf causes the animation to loop continuously. Setting DelayTime to 1 specifies a 1-second delay between the display of each image in the animation.

Input Arguments

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Image data, specified as a full (nonsparse) matrix.

• For grayscale images, A can be_m_-by-n.
• For indexed images, A can be_m_-by-n. Specify the associated colormap in the map input argument.
• For truecolor images, A must be_m_-by-_n_-by-3. imwrite does not support writing RGB images to GIF files.

For TIFF files, A can be an_m_-by-_n_-by-4 array containing color data that uses the CMYK color space.

For multiframe GIF files, A can be an_m_-by-_n_-by-1-by-p array containing grayscale or indexed images, where p is the number of frames to write. RGB images are not supported in this case.

Data Types: double | single | uint8 | uint16 | logical

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

Depending on the location you are writing to, filename can take on one of these forms.

Data Types: char | string

Colormap associated with indexed image data in A, specified as an_m_-by-3 array. map must be a valid MATLAB® colormap. See colormap for a list of built-in MATLAB colormaps. Most image file formats do not support colormaps with more than 256 entries.

Example: [0,0,0; 0.5,0.5,0.5; 1,1,1]

Example: jet(60)

Data Types: double

Format of the output file, specified as one of the formats in this table.

This table also summarizes the types of images that imwrite can write. The MATLAB file format registry determines which file formats are supported. See imformats for more information about this registry.

For certain formats, imwrite can accept additional name-value arguments. To view these arguments, click the linked format names below.

Name-Value Arguments

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Specify optional pairs of arguments asName1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: imwrite(A,"myFile.png",BitDepth=8) writes the data inA using 8 bits to represent each pixel.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: imwrite(A,"myFile.png","BitDepth",8) writes the data inA using 8 bits to represent each pixel.

GIF — Graphics Interchange Format

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Color to use as background color for the indexed image, specified as a nonnegative integer scalar corresponding to the colormap index.

The background color is used for some disposal methods in animated GIFs.

• If image data A is uint8 orlogical, then the colormap index is zero-based.
• If image data A is double, then the colormap index is one-based.

The default background color corresponds to the first color in the colormap.

Example: "BackgroundColor",15

Data Types: string | char | cell

Delay before displaying next image, in seconds, specified as a scalar value in the range [0, 655].

Tip

To achieve a high animation rate, set DelayTime to0.02. Setting DelayTime to a lower value will slow down the actual animation rate in many image viewers and web browsers.

Example: "DelayTime",60

Disposal method of an animated GIF, specified as one of the methods in this table.

Example: "DisposalMethod","restoreBG"

Offset of the screen relative to the image, measured from the top-left corner of each, specified as a two-element vector. The first vector element specifies the offset from the top, and the second element specifies the offset from the left, in pixels.

Example: "Location",[10,15]

Data Types: double

Number of times to repeat the animation, specified as either an integer in the range [0, 65,535] or the value Inf. If you specify the value0, the animation plays once; if you specify the value1, the animation plays twice, and so on. ALoopCount value of Inf causes the animation to loop continuously.

To enable animation within Microsoft® PowerPoint®, specify a value for LoopCount within the range [1, 65,535]. Some Microsoft applications interpret the value 0 to mean not to loop at all.

Example: "LoopCount",3

Height and width of the frame, specified as a two-element vector. You can useScreenSize argument with Location to write frames to the image that are smaller than the whole frame.DisposalMethod determines the fill value for pixels outside the frame.

Example: "ScreenSize",[1000 1060]

Data Types: double

Color to use as transparent color for the image, specified as a nonnegative integer scalar corresponding to the colormap index.

• If image data A is uint8 orlogical, then indexing begins at 0.
• If image data A is double, then indexing begins at 1.

Example: "TransparentColor",20

Writing mode, specified as "overwrite" or"append". In "overwrite" mode,imwrite overwrites an existing file,filename. In "append" mode,imwrite adds a single frame to the existing file.

Example: "WriteMode","append"

HDF4 — Hierarchical Data Format

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Compression scheme, specified as one of the options in this table.

Example: "Compression","jpeg"

Quality of the JPEG-compressed file, specified as a scalar in the range [0, 100], where 0 is lower quality and higher compression, and 100 is higher quality and lower compression. This parameter applies only if Compression is"jpeg".

Example: "Quality",25

Writing mode, specified as "overwrite" or"append". In "overwrite" mode,imwrite overwrites an existing file,filename. In "append" mode,imwrite adds a single frame to the existing file.

Example: "WriteMode","append"

JPEG — Joint Photographic Experts Group

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Number of bits per pixel, specified as a scalar.

• For grayscale images, the BitDepth value can be8, 12, or 16. The default value is 8. For 16-bit images, theMode name-value argument must be"lossless".
• For color images, the BitDepth value is the number of bits per plane, and can be 8 or 12. The default is 8 bits per plane.

Example: "BitDepth",12

Data Types: string | char | cell

Type of compression, specified as "lossy" or"lossless".

Example: "Mode","lossless"

Quality of the output file, specified as a scalar in the range [0, 100], where 0 is lower quality and higher compression, and 100 is higher quality and lower compression. A Quality value of 100 does not write a lossless JPEG image. Instead, set the Mode name-value argument to"lossless".

Example: "Quality",100

JPEG 2000— Joint Photographic Experts Group 2000

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Data Types: string | char | cell

Target compression ratio, specified as a positive scalar greater than or equal to 1. The compression ratio is the ratio of the input image size to the output compressed size. For example, a value of 2 implies that the output image size is half of the input image size or less. A higher value implies a smaller file size and more reduced image quality. The compression ratio does not take into account the header size.

Specifying CompressionRatio is valid only whenMode is "lossy".

Example: "CompressionRatio",3

Type of compression, specified as "lossy" or"lossless".

Example: "Mode","lossless"

Order of packets in the code stream, specified as one of these options:

• "LRCP"
• "RLCP"
• "RPCL"
• "PCRL"
• "CPRL"

The characters represent these packets: L = layer,R = resolution, C = component, andP = position.

Example: "ProgressionOrder","RLCP"

Number of quality layers, specified as an integer in the range [1, 20].

Example: "QualityLayers",8

Number of reduction levels, or wavelet decomposition levels, specified as an integer in the range [1, 8].

Example: "ReductionLevels",6

Tile height and width, specified as a two-element vector. The minimum size you can specify is [128 128].

Example: "TileSize",[130 130]

PBM, PGM, and PPM — Portable Bitmap, Graymap, Pixmap

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Encoding, specified as "rawbits" for binary encoding or"ASCII" for plain encoding.

Example: "Encoding","ASCII"

Maximum gray or color value, specified as a positive integer scalar.

Specify this name-value argument only for PGM and PPM files. For PBM files, this value is always 1.

If the image array is uint16, then the default value forMaxValue is 65535. Otherwise, the default value is 255.

Example: "MaxValue",510

PNG — Portable Network Graphics

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Transparency of each pixel, specified as a matrix of values in the range [0, 1]. The row and column dimensions of the Alpha matrix must be the same as those of the image data array. You can specify Alpha only for grayscale (_m_-by-n) and truecolor (_m_-by-_n_-by-3) image data.

Note

You cannot specify both Alpha andTransparency at the same time.

Data Types: double | uint8 | uint16

Data Types: string | char

Background color when compositing transparent pixels, specified as a value dependent on the image data, as shown in this table.

Data Types: double

Number of bits per pixel, specified as a scalar. Depending on the output image, the scalar can be one of these values.

• If the image is of type double or uint8, then the default bit depth is 8 bits per pixel.
• If the image is of type uint16, then the default is 16 bits per pixel.
• If the image is of type logical, then the default is 1 bit per pixel.

Example: "BitDepth",4

Reference white point and primary chromaticities, specified as an eight-element vector of the form [wx wy rx ry gx gy bx by]. The elementswx and wy are the chromaticity coordinates of the white point, and the elements rx, ry,gx, gy, bx, andby are the chromaticity coordinates of red, green, and blue, respectively.

If you specify Chromaticities, you should also specify theGamma name-value argument.

Example: "Chromaticities",[0.312,0.329,0.002,0.002,0.001,0.001,0.115,0.312]

Data Types: double

Copyright notice, specified as a string scalar or character vector.

Time of original image creation, specified as either a datetime, or a string scalar or character vector that represents a point in time. If you specifyCreationTime as a datetime value with a time zone, then imwrite stores the time zone as part of the value.

Example: "CreationTime",datetime("1955-11-12 10:04 PM","TimeZone","America/Los_Angeles")

Description of the image, specified as a string scalar or character vector.

Legal disclaimer, specified as a string scalar or character vector.

File gamma, specified as a numeric scalar.

Example: "Gamma",2.2

Time of last image modification, specified as either a datetime, or a string scalar or character vector that represents a point in time. If you specifyImageModTime as a datetime value with a time zone other than UTC, then imwrite converts the value to UTC before storing it. If you specify ImageModTime as adatetime value without a time zone, thenimwrite interprets the value as UTC.

The default ImageModTime value is the time when you callimwrite.

Example: "ImageModTime",datetime("2018-04-01 9:00 AM","TimeZone","Europe/Rome")

Interlacing scheme, specified as "none" for no interlacing or"adam7" to use the Adam7 algorithm.

Example: "InterlaceType","adam7"

Unit for image resolution, specified as "unknown" or"meter". If you specify ResolutionUnit, you must include at least one of the XResolution andYResolution name-value arguments. When the value ofResolutionUnit is "meter", theXResolution and YResolution values are interpreted as pixels per meter.

Example: "ResolutionUnit","meter","XResolution",1000

Number of bits in the data array to regard as significant, specified as a scalar or a vector in the range [1, BitDepth]. Depending on the output image type, the value must be in the following form.

Example: "SignificantBits",[2,3]

Software used to create the image, specified as a string scalar or character vector.

Device used to create the image, specified as a string scalar or character vector.

Pixels to consider transparent when no alpha channel is used, specified as a scalar or vector. Depending on the output image, the value must be in the following form.

Note

You cannot specify both Transparency andAlpha at the same time.

Example: "Transparency",[1 1 1]

Data Types: double

Warning of nature of content, specified as a string scalar or character vector.

Image resolution in the horizontal direction, in pixels/unit, specified as a numeric scalar. Define the unit by specifying the ResolutionUnit name-value argument.

If you do not also specify YResolution, then theXResolution value applies to both the horizontal and vertical directions.

Example: "XResolution",900

Image resolution in the vertical direction, in pixels/unit, specified as a numeric scalar. Define the unit by specifying the ResolutionUnit name-value argument.

If you do not also specify XResolution, then theYResolution value applies to both the vertical and horizontal directions.

Example: "YResolution",900

In addition to the listed name-value arguments for PNG, you can use any parameter name that satisfies the PNG specification for keywords. That is, the name uses only printable characters, contains 80 or fewer characters, and does not contain leading or trailing spaces. The value corresponding to these user-specified names must be a string scalar or character vector that contains no control characters other than linefeeds.

RAS — Sun Raster Graphic

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Transparency of each pixel, specified as a matrix with row and column dimensions the same as those of the image data array.

This name-value argument is valid only for truecolor (_m_-by-_n_-by-3) image data.

Data Types: double | single | uint8 | uint16

Image type, specified as one of the options in this table.

Example: "Type","rgb"

TIFF — Tagged Image File Format

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Color space representing the color data, specified as "rgb","cielab", or "icclab".

This name-value argument is valid only when the image data array,A, is truecolor (_m_-by-_n_-by-3). To use the CMYK color space in a TIFF file, do not use the ColorSpace name-value argument. Instead, specify an _m_-by-_n_-by-4 image data array.

imwrite can write color image data that uses the_L*a*b*_ color space to TIFF files. The 1976 CIE_L*a*b*_ specification defines numeric values that represent luminance (L*) and chrominance (a* and_b*_) information. To store L*a*b* color data in a TIFF file, the values must be encoded to fit into either 8-bit or 16-bit storage. imwrite can store L*a*b* color data in a TIFF file using these encodings:

• CIELAB encodings — 8-bit and 16-bit encodings defined by the TIFF specification
• ICCLAB encodings — 8-bit and 16-bit encodings defined by the International Color Consortium

The output class and encoding used by imwrite depends on the class of the input image data array and the ColorSpace value, as shown in this table. (The 8-bit and 16-bit CIELAB encodings cannot be input arrays because they use a mixture of signed and unsigned values and cannot be represented as a single MATLAB array.)

Example: "ColorSpace","cielab"

Compression scheme, specified as one of these options:

• "packbits" (default for nonbinary images)
• "none"
• "lzw"
• "deflate"
• "jpeg"
• "ccitt" (binary images only, and the default for such images)
• "fax3" (binary images only)
• "fax4" (binary images only)

"jpeg" is a lossy compression scheme; other compression modes are lossless. Also, if you specify "jpeg" compression, you must specify the RowsPerStrip name-value argument and the value must be a multiple of 8.

Example: "Compression","none"

Image description, specified by a string scalar or character vector. This description is the text that imfinfo returns in theImageDescription field for the output image.

Example: "Description","Sample 2A301"

X- and Y-resolution, specified as a scalar indicating both X-resolution and Y-resolution, or a two-element vector containing the X-resolution and the Y-resolution.

Example: "Resolution",80

Example: "Resolution",[320,72]

Data Types: double

Number of rows to include in each strip, specified as a scalar. The default value is such that each strip is about 8 kilobytes.

You must specify RowsPerStrip if you specify"jpeg" compression. In this case, the value must be a multiple of 8.

Example: "RowsPerStrip",16

Data Types: double | single | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Writing mode, specified as "overwrite" or"append". In "overwrite" mode,imwrite overwrites an existing file. In"append" mode, imwrite adds a page to the existing file.

Example: "WriteMode","append"

Extended Capabilities

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The imwrite function supports GPU array input with these usage notes and limitations:

• This function accepts GPU arrays, but does not run on a GPU.

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced before R2006a

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You can use datetime values to specify theCreationTime and ImageModTime name-value arguments.

You can run imwrite in the background using MATLABbackgroundPool.

Pixel value differences might exist between JPEG 2000 images in R2021b and previous releases of MATLAB.

When writing indexed PNG files, you must specify a colormap with enough entries to interpret the image correctly.