# TIFF Metadata Format Specification and Usage Notes

Reading Images

- Color Conversion
- Color Spaces
- ICC Profiles
- Metadata Issues
  - Native to Standard Metadata Mapping
- Reading Exif Images
  - Reading Uncompressed Exif Images
  - Reading Compressed Exif Images

Writing Images

- Compression
- Color Conversion
- ICC Profiles
- Metadata Issues
  - Standard to Native Metadata Mapping
- Writing Exif Images
  - Writing Uncompressed Exif Images
  - Writing Compressed Exif Images

Native Stream Metadata Format
Native Image Metadata Format

## Reading Images

TIFF images are read by an `ImageReader` which may be controlled by its public interface as well as via a supplied `TIFFImageReadParam`.

### Color Conversion

If the source image data have photometric type CIE L*a*b* or YCbCr, and the destination color space type is RGB, then the source image data will be automatically converted to RGB using an internal color converter.

### Color Spaces

The raw color space assigned by default, i.e., in the absence of a user-supplied `ImageTypeSpecifier`, will be the first among the following which applies:

- A color space created from the ICC Profile metadata field if it is present and compatible with the image data layout.
- sRGB if the image is monochrome/bilevel (a two-level color map is created internally).
- sRGB if the image is palette-color.
- Linear RGB if the image has three samples per pixel, has photometric type CIE L*a*b*, or has photometric type YCbCr and is not JPEG-compressed.
- A default CMYK color space if the image has photometric type CMYK and four samples per pixel.
- Grayscale if the image has one or two samples per pixel and uniformly 1, 2, 4, 8, 16, or 32 bits per sample or is floating point.
- sRGB if the image has three or four samples per pixel and uniformly 1, 2, 4, 8, 16, or 32 bits per sample or is floating point.
- A fabricated, generic color space if the image has more than four samples per pixel and the number of bits per sample for all bands is the same and is a multiple of 8.
- Grayscale if the image has one or two samples per pixel regardless of the number of bits per sample.
- sRGB if the image has three or four samples per pixel regardless of the number of bits per sample.
- A fabricated, generic color space if the image has more than four samples per pixel regardless of the number of bits per sample.

The normalized color coordinate transformations used for the default CMYK color space are defined as follows:

- CMYK to linear RGB

      R = (1 - K)*(1 - C)
      G = (1 - K)*(1 - M)
      B = (1 - K)*(1 - Y)

- Linear RGB to CMYK

      K = min{1 - R, 1 - G, 1 - B}
      if(K != 1) {
          C = (1 - R - K)/(1 - K)
          M = (1 - G - K)/(1 - K)
          Y = (1 - B - K)/(1 - K)
      } else {
          C = M = Y = 0
      }

The generic color space used when no other color space can be inferred is provided merely to enable the data to be loaded. It is not intended to provide accurate conversions of any kind.

If the data are known to be in a color space not correctly handled by the foregoing, then an `ImageTypeSpecifier` should be supplied to the reader and should be derived from a color space which is correct for the data in question.

### ICC Profiles

If an ICC profile is contained in the image metadata (`BaselineTIFFTagSet`. TAG_ICC_PROFILE, tag number 34675), an attempt will be made to use it to create the color space of the loaded image. It will be used if the data layout is of component type and the number of samples per pixel equals or is one greater than the number of components described by the ICC profile. If the ICC profile is not used then the color space will be inferred in one of the subsequent steps described above.

If for some reason the embedded ICC profile is not used automatically, then it may be used manually by following this procedure:

1. Obtain the image metadata from `ImageReader.getImageMetadata`
2. Extract the ICC profile field and its value.
3. Create an `ICC_ColorSpace` from an `ICC_Profile` created from the ICC profile field data using `ICC_Profile.getInstance(byte[])`.
4. Create an `ImageTypeSpecifier` from the new color space using one of its factory methods which accepts an `ICC_ColorSpace`.
5. Create a compatible `ImageReadParam` and set the `ImageTypeSpecifier` using `ImageReadParam.setDestinationType`.
6. Pass the parameter object to the appropriate `read` method.

If the inferred color space not based on the ICC Profile field is compatible with the ICC profile-based color space, then a second `ImageTypeSpecifier` derived from this inferred color space will be included in the `Iterator` returned by `ImageReader.getImageTypes`. If the iterator contains more than one type, the first one will be based on the ICC profile and the second on the inferred color space.

### Metadata Issues

By default all recognized fields in the TIFF image file directory (IFD) are loaded into the native image metadata object. Which fields are loaded may be controlled by setting which TIFF tags the reader is allowed to recognize, whether to read fields with unrecognized tags, and whether to ignore all metadata. The reader is informed to disregard all metadata as usual via the `ignoreMetadata` parameter of `ImageReader.setInput(Object,boolean,boolean)`. It is informed of which `TIFFTag`s to recognize or not to recognize via `TIFFImageReadParam.addAllowedTagSet(TIFFTagSet)` and `TIFFImageReadParam.removeAllowedTagSet(TIFFTagSet)`. If `ignoreMetadata` is `true`, then only metadata essential to reading the image will be loaded into the native image metadata object. If `ignoreMetadata` is `false`, then the reader will by default load into the native image metadata object only those fields which are either essential to reading the image or have a `TIFFTag` contained in the one of the allowed `TIFFTagSet`s. Reading of fields with tags not in the allowed `TIFFTagSet`s may be forced by passing in a `TIFFImageReadParam` on which `TIFFImageReadParam.setReadUnknownTags(boolean)` has been invoked with parameter `true`.

Use of a `TIFFDirectory` object may simplify gaining access to metadata values. An instance of `TIFFDirectory` may be created from the `IIOMetadata` object returned by the TIFF reader using the `TIFFDirectory.createFromMetadata` method.

#### Mapping of TIFF Native Image Metadata to the Standard Metadata Format

The derivation of standard metadata format javax_imageio_1.0 elements from TIFF native image metadata is given in the following table.
Index | Standard Metadata Element | Derivation from TIFF Fields
--- | --- | ---
1 | /Chroma/ColorSpaceType@name | PhotometricInterpretation: WhiteIsZero, BlackIsZero, TransparencyMask = "GRAY"; RGB, PaletteColor => "RGB"; CMYK => "CMYK"; YCbCr => "YCbCr"; CIELab, ICCLab => "Lab".
2 | /Chroma/NumChannels@value | SamplesPerPixel
3 | /Chroma/BlackIsZero@value | "TRUE" <=> PhotometricInterpretation => WhiteIsZero
4 | /Chroma/Palette | ColorMap
5 | /Compression/CompressionTypeName@value | Compression: Uncompressed => "none"; CCITT 1D => "CCITT RLE"; Group 3 Fax => "CCITT T.4"; Group 4 Fax => "CCITT T.6"; LZW => "LZW"; JPEG => "Old JPEG"; New JPEG => "JPEG"; Zlib =>> "ZLib"; PackBits => "PackBits"; Deflate => "Deflate"; Exif JPEG => "JPEG".
6 | /Compression/Lossless@value | Compression: JPEG or New JPEG => "FALSE"; otherwise "TRUE".
7 | /Data/PlanarConfiguration@value | Chunky => "PixelInterleaved"; Planar => "PlaneInterleaved".
8 | /Data/SampleFormat@value | PhotometricInterpretation PaletteColor => "Index"; SampleFormat unsigned integer data => "UnsignedIntegral"; SampleFormat two's complement signed integer data => "SignedIntegral"; SampleFormat IEEE floating point data => "Real"; otherwise element not emitted.
9 | /Data/BitsPerSample@value | BitsPerSample as a space-separated list.
10 | /Data/SampleMSB@value | FillOrder: left-to-right => space-separated list of BitsPerSample-1; right-to-left => space-separated list of 0s.
11 | /Dimension/PixelAspectRatio@value | (1/XResolution)/(1/YResolution)
12 | /Dimension/ImageOrientation@value | Orientation
13 | /Dimension/HorizontalPixelSize@value | 1/XResolution in millimeters if ResolutionUnit is not None.
14 | /Dimension/VerticalPixelSize@value | 1/YResolution in millimeters if ResolutionUnit is not None.
15 | /Dimension/HorizontalPosition@value | XPosition in millimeters if ResolutionUnit is not None.
16 | /Dimension/VerticalPosition@value | YPosition in millimeters if ResolutionUnit is not None.
17 | /Document/FormatVersion@value | 6.0
18 | /Document/SubimageInterpretation@value | NewSubFileType: transparency => "TransparencyMask"; reduced-resolution => "ReducedResolution"; single page => "SinglePage".
19 | /Document/ImageCreationTime@value | DateTime
20 | /Text/TextEntry | DocumentName, ImageDescription, Make, Model, PageName, Software, Artist, HostComputer, InkNames, Copyright: /Text/TextEntry@keyword = field name, /Text/TextEntry@value = field value. Example: TIFF Software field => /Text/TextEntry@keyword = "Software", /Text/TextEntry@value = Name and version number of the software package(s) used to create the image.
21 | /Transparency/Alpha@value | ExtraSamples: associated alpha => "premultiplied"; unassociated alpha => "nonpremultiplied".

### Reading Exif Images

The TIFF reader may be used to read an uncompressed Exif image or the contents of the `APP1` marker segment of a compressed Exif image.

#### Reading Uncompressed Exif Images

An uncompressed Exif image is a one- or two-page uncompressed TIFF image with a specific ordering of its IFD and image data content. Each pixel has three 8-bit samples with photometric interpretation RGB or YCbCr. The image stream must contain a single primary image and may contain a single thumbnail which if present must also be uncompressed. The usual `ImageReader` methods may be used to read the image data and metadata:

        ImageInputStream input;
        ImageReader tiffReader;
        ImageReadParam tiffReadParam;

        tiffReader.setInput(input);

        // Read primary image and IFD.
        BufferedImage image = tiffReader.read(0, tiffReadParam);
        IIOMetadata primaryIFD = tiffReader.getImageMetadata(0);

        // Read thumbnail if present.
        BufferedImage thumbnail = null;
        if (tiffReader.getNumImages(true) > 1) {
            thumbnail = tiffReader.read(1, tiffReadParam);
        }

Note that the Exif thumbnail is treated as a separate page in the TIFF stream and not as a thumbnail, i.e., `tiffReader.hasThumbnails(0)` will return `false`.

#### Reading Compressed Exif Images

A compressed Exif image is a 3-band ISO/IEC 10918-1 baseline DCT JPEG stream with an inserted `APP1` marker segment. The parameters of the marker segment after the length are the 6-byte sequence `{'E', 'x', 'i', 'f', 0x00, 0x00}` followed by a complete TIFF stream. The embedded TIFF stream contains a primary IFD describing the JPEG image optionally followed by a thumbnail IFD and compressed or uncompressed thumbnail image data. Note that the embedded TIFF stream does not contain any image data associated with the primary IFD nor any descriptive fields which duplicate information found in the JPEG stream itself.

The parameter content of the `APP1` marker segment may be obtained from the user object of the associated `Node` in a `javax_imageio_jpeg_image_1.0` native image metadata tree extracted from the image metadata object returned by the JPEG reader. This APP1 Exif node will be a child of the node named "markerSequence" and will have name `unknown` and an attribute named `MarkerTag` with integral value `0xE1` (`String` value `"225"`). The user object of this node will be a byte array which starts with the six bytes `{'E', 'x', 'i', 'f', '0', '0'}`. The primary IFD and the thumbnail IFD and image may be read from the user object by the usual `ImageReader` methods:

        ImageReader jpegReader;
        ImageReader tiffReader;

        // Obtain the APP1 Exif marker data from the JPEG image metadata.
        IIOMetadata jpegImageMetadata = jpegReader.getImageMetadata(0);
        String nativeFormat = jpegImageMetadata.getNativeMetadataFormatName();
        Node jpegImageMetadataTree = jpegImageMetadata.getAsTree(nativeFormat);

        // getExifMarkerData() returns the byte array which is the user object
        // of the APP1 Exif marker node.
        byte[] app1Params = getExifMarkerData(jpegImageMetadataTree);
        if (app1Params == null) {
            throw new IIOException("APP1 Exif marker not found.");
        }

        // Set up input, skipping Exif ID 6-byte sequence.
        MemoryCacheImageInputStream app1ExifInput
            = new MemoryCacheImageInputStream
                (new ByteArrayInputStream(app1Params, 6, app1Params.length - 6));
        tiffReader.setInput(app1ExifInput);

        // Read primary IFD.
        IIOMetadata primaryIFD = tiffReader.getImageMetadata(0);

        // Read thumbnail if present.
        BufferedImage thumbnail = null;
        if (tiffReader.getNumImages(true) > 1) {
            thumbnail = tiffReader.read(1, tiffReadParam);
        }

        // Read the primary image.
        BufferedImage image = jpegReader.read(0);

Note that `tiffReader.getNumImages(true)` returns the number of IFDs in the embedded TIFF stream including those corresponding to empty images. Calling `tiffReader.read(0, readParam)` will throw an exception as the primary image in the embedded TIFF stream is always empty; the primary image should be obtained using the JPEG reader itself.

## Writing Images

TIFF images are written by a `ImageWriter` which may be controlled by its public interface as well as via a supplied `ImageWriteParam`. For an `ImageWriteParam` returned by the `getDefaultWriteParam()` method of the TIFF `ImageWriter`, the `canWriteTiles()` and `canWriteCompressed()` methods will return `true`; the `canOffsetTiles()` and `canWriteProgressive()` methods will return `false`. The TIFF writer supports many optional capabilities including writing tiled images, inserting images, writing or inserting empty images, and replacing image data. Pixels may be replaced in either empty or non-empty images but if and only if the data are not compressed.

If tiles are being written, then each of their dimensions will be rounded to the nearest multiple of 16 per the TIFF specification. If JPEG-in-TIFF compression is being used, and tiles are being written each tile dimension will be rounded to the nearest multiple of 8 times the JPEG minimum coded unit (MCU) in that dimension. If JPEG-in-TIFF compression is being used and strips are being written, the number of rows per strip is rounded to a multiple of 8 times the maximum MCU over both dimensions.

### Compression

The compression type may be set via the `setCompressionType()` method of the `ImageWriteParam` after setting the compression mode to `MODE_EXPLICIT`. The set of innately supported compression types is listed in the following table:

Supported Compression Types
Index | Compression Type | Description | Reference
--- | --- | --- | ---
1 | CCITT RLE | Modified Huffman compression | TIFF 6.0 Specification, Section 10
2 | CCITT T.4 | CCITT T.4 bilevel encoding/Group 3 facsimile compression | TIFF 6.0 Specification, Section 11
3 | CCITT T.6 | CCITT T.6 bilevel encoding/Group 4 facsimile compression | TIFF 6.0 Specification, Section 11
4 | LZW | LZW compression | TIFF 6.0 Specification, Section 13
5 | JPEG | "New" JPEG-in-TIFF compression | TIFF Technical Note #2
6 | ZLib | "Deflate/Inflate" compression (see note following this table) | Adobe Photoshop® TIFF Technical Notes
7 | PackBits | Byte-oriented, run length compression | TIFF 6.0 Specification, Section 9
8 | Deflate | "Zip-in-TIFF" compression (see note following this table) | ZLIB Compressed Data Format Specification, DEFLATE Compressed Data Format Specification
9 | Exif JPEG | Exif-specific JPEG compression (see note following this table) | Exif 2.3 Specification (PDF), section 4.5.8, "Basic Structure of Thumbnail Data"

Old-style JPEG compression as described in section 22 of the TIFF 6.0 Specification is not supported.

The CCITT compression types are applicable to bilevel (1-bit) images only. The JPEG compression type is applicable to byte grayscale (1-band) and RGB (3-band) images only.

ZLib and Deflate compression are identical except for the value of the TIFF Compression field: for ZLib the Compression field has value 8 whereas for Deflate it has value 32946 (0x80b2). In both cases each image segment (strip or tile) is written as a single complete zlib data stream.

"Exif JPEG" is a compression type used when writing the contents of an APP1 Exif marker segment for inclusion in a JPEG native image metadata tree. The contents appended to the output when this compression type is used are a function of whether an empty or non-empty image is written. If the image is empty, then a TIFF IFD adhering to the specification of a compressed Exif primary IFD is appended. If the image is non-empty, then a complete IFD and image adhering to the specification of a compressed Exif thumbnail IFD and image are appended. Note that the data of the empty image may not later be appended using the pixel replacement capability of the TIFF writer.

If ZLib/Deflate or JPEG compression is used, the compression quality may be set. For ZLib/Deflate the supplied floating point quality value is rescaled to the range `[1, 9]` and truncated to an integer to derive the Deflate compression level. For JPEG the floating point quality value is passed directly to the JPEG writer plug-in which interprets it in the usual way.

### Color Conversion

If the source image data color space type is RGB, and the destination photometric type is CIE L*a*b* or YCbCr, then the source image data will be automatically converted from RGB using an internal color converter.

### ICC Profiles

An `ICC Profile` field will be written if either:

- one is present in the native image metadata `IIOMetadata` instance supplied to the writer, or
- the `ColorSpace` of the destination `ImageTypeSpecifier` is an instance of `ICC_ColorSpace` which is not one of the standard color spaces defined by the `CS_*` constants in the `ColorSpace` class. The destination type is set via `ImageWriteParam.setDestinationType(ImageTypeSpecifier)` and defaults to the `ImageTypeSpecifier` of the image being written.

### Metadata Issues

Some behavior of the writer is affected by or may affect the contents of the image metadata which may be supplied by the user.

For bilevel images, the `FillOrder`, and `T4Options` fields affect the output data. The data will be filled right-to-left if `FillOrder` is present with a value of 2 (`BaselineTIFFTagSet.FILL_ORDER_RIGHT_TO_LEFT`) and will be filled left-to-right otherwise. The value of `T4Options` specifies whether the data should be 1D- or 2D-encoded and whether EOL padding should be used.

For all images the value of the `RowsPerStrip` field is used to the set the number of rows per strip if the image is not tiled. The default number of rows per strip is either 8 or the number of rows which would fill no more than 8 kilobytes, whichever is larger.

For all images the tile dimensions may be set using the `TileWidth` and `TileLength` field values if the tiling mode is `ImageWriteParam.MODE_COPY_FROM_METADATA`. If this mode is set but the fields are not, their respective default values are the image width and height.

When using JPEG-in-TIFF compression, a `JPEGTables` field will be written to the IFD and abbreviated JPEG streams to each strip or tile if and only if a `JPEGTables` field is contained in the metadata object provided to the writer. If the contents of the `JPEGTables` field is a valid tables-only JPEG stream, then it will be used; otherwise the contents of the field will be replaced with default visually lossless tables. If no such `JPEGTables` field is present in the metadata, then no `JPEGTables` field will be written to the output and each strip or tile will be written as a separate, self-contained JPEG stream.

When using Deflate/ZLib or LZW compression, if the image has 8 bits per sample, a horizontal differencing predictor will be used if the `Predictor` field is present with a value of 2 (`BaselineTIFFTagSet.PREDICTOR_HORIZONTAL_DIFFERENCING`). If prediction is so requested but the image does not have 8 bits per sample the field will be reset to have the value 1 (`BaselineTIFFTagSet.PREDICTOR_NONE`).

Some fields may be added or modified:

- `PhotometricInterpretation` if not present.
- `PlanarConfiguration` if this field is present with value `Planar` is is reset to `Chunky`.
- `Compression` always.
- `BitsPerSample` if the image is not bilevel.
- `SamplesPerPixel` always.
- `ExtraSamples` if an alpha channel is present.
- `SampleFormat` if not present and the data are 16- or 32-bit integers or floating point.
- `ColorMap` if the `PhotometricInterpretation` is `RGBPalette`.
- `ImageWidth` and `ImageLength` always.
- `TileWidth`, `TileLength`, `TileOffsets`, and `TileByteCounts` if a tiled image is being written.
- `RowsPerStrip`, `StripOffsets`, and `StripByteCounts` if a tiled image is not being written.
- `XResolution`, `YResolution`, and `ResolutionUnit` if none of these is present.
- `YCbCrSubsampling` and `YCbCrPositioning` if the photometric interpretation is YCbCr and the compression type is not JPEG (only [1, 1] subsampling and cosited positioning are supported for non-JPEG YCbCr output).
- `YCbCrSubsampling`, `YCbCrPositioning`, and `ReferenceBlackWhite`: if the compression type is JPEG and the color space is RGB these will be reset to [2, 2] centered subsampling with no headroom/footroom (0:255,128:255,128:255).

Some fields may be removed:

- `BitsPerSample` if the image is bilevel.
- `ExtraSamples` if the image does not have an alpha channel.
- `ColorMap` if the photometric interpretation is not `RGBPalette`.
- `TileWidth`, `TileLength`, `TileOffsets`, and `TileByteCounts` if tiling is not being used.
- `RowsPerStrip`, `StripOffsets`, and `StripByteCounts` if tiling is being used.
- `YCbCrSubsampling`, `YCbCrPositioning`, and `ReferenceBlackWhite` if the compression type is JPEG and the color space is grayscale.
- `JPEGProc`, `JPEGInterchangeFormat`, `JPEGInterchangeFormatLength`, `JPEGRestartInterval`, `JPEGLosslessPredictors`, `JPEGPointTransforms`, `JPEGQTables`, `JPEGDCTables`, and `JPEGACTables` if the compression type is JPEG.

Other fields present in the supplied metadata are uninterpreted and will be written as supplied.

If an Exif image is being written, the set of fields present and their values will be modified such that the result is in accord with the Exif 2.3 specification.

Setting up the image metadata to write to a TIFF stream may be simplified by using the `TIFFDirectory` class which represents a TIFF IFD. A field in a TIFF IFD is represented by an instance of `TIFFField`. For each field to be written a `TIFFField` may be added to the `TIFFDirectory` and the latter converted to an `IIOMetadata` object by invoking `TIFFDirectory.getAsMetadata`. The `IIOMetadata` object so obtained may then be passed to the TIFF writer.

#### Mapping of the Standard Metadata Format to TIFF Native Image Metadata

The derivation of TIFF native image metadata elements from the standard metadata format javax_imageio_1.0 is given in the following table.
Index | TIFF Field | Derivation from Standard Metadata Elements
--- | --- | ---
1 | PhotometricInterpretation | /Chroma/ColorSpaceType@name: "GRAY" and /Chroma/BlackIsZero@value = "FALSE" => WhiteIsZero; "GRAY" and /Document/SubimageInterpretation@value = "TransparencyMask" => TransparencyMask; "RGB" and /Chroma/Palette present => PaletteColor; "GRAY" => BlackIsZero; "RGB" => RGB; "YCbCr" => YCbCr; "CMYK" => CMYK; "Lab" => CIELab.
2 | SamplesPerPixel | /Chroma/NumChannels@value
3 | ColorMap | /Chroma/Palette
4 | Compression | /Compression/CompressionTypeName@value: "none" => Uncompressed; "CCITT RLE" => CCITT 1D; "CCITT T.4" => Group 3 Fax; "CCITT T.6" => Group 4 Fax; "LZW" => LZW; "Old JPEG" => JPEG; "JPEG" => New JPEG; "ZLib" => ZLib; "PackBits" => PackBits; "Deflate" => Deflate.
5 | PlanarConfiguration | /Data/PlanarConfiguration@value: "PixelInterleaved" => Chunky; "PlaneInterleaved" => Planar.
6 | SampleFormat | /Data/SampleFormat@value: "SignedIntegral" => two's complement signed integer data; "UnsignedIntegral" => unsigned integer data; "Real" => IEEE floating point data; "Index" => unsigned integer data.
7 | BitsPerSample | /Data/BitsPerSample@value: space-separated list parsed to char array.
8 | FillOrder | /Data/SampleMSB@value: if all values in space-separated list are 0s => right-to-left; otherwise => left-to-right.
9 | XResolution | (10 / /Dimension/HorizontalPixelSize@value) or (10 / (/Dimension/VerticalPixelSize@value * /Dimension/PixelAspectRatio@value))
10 | YResolution | (10 / /Dimension/VerticalPixelSize@value) or (10 / (/Dimension/HorizontalPixelSize@value / /Dimension/PixelAspectRatio@value))
11 | ResolutionUnit | Centimeter if XResolution or YResolution set; otherwise None.
12 | Orientation | /Dimension/ImageOrientation@value
13 | XPosition | /Dimension/HorizontalPosition@value / 10
14 | YPosition | /Dimension/VerticalPosition@value / 10
15 | NewSubFileType | /Document/SubimageInterpretation@value: "TransparencyMask" => transparency mask; "ReducedResolution" => reduced-resolution; "SinglePage" => single page.
16 | DateTime | /Document/ImageCreationTime@value
17 | DocumentName, ImageDescription, Make, Model, PageName, Software, Artist, HostComputer, InkNames, Copyright | /Text/TextEntry: if /Text/TextEntry@keyword is the name of any of the TIFF Fields, e.g., "Software", then the field is added with content /Text/TextEntry@value and count 1.
18 | ExtraSamples | /Transparency/Alpha@value: "premultiplied" => associated alpha, count 1; "nonpremultiplied" => unassociated alpha, count 1.

### Writing Exif Images

The TIFF writer may be used to write an uncompressed Exif image or the contents of the `APP1` marker segment of a compressed Exif image.

#### Writing Uncompressed Exif Images

When writing a sequence of images each image is normally recorded as {IFD, IFD Value, Image Data}. The Exif specification requires that an uncompressed Exif image be structured as follows:

1. Image File Header
2. Primary IFD
3. Primary IFD Value
4. Thumbnail IFD
5. Thumbnail IFD Value
6. Thumbnail Image Data
7. Primary Image Data

To meet the requirement of the primary image data being recorded last, the primary image must be written initially as an empty image and have its data added via pixel replacement after the thumbnail IFD and image data have been written:

        ImageWriter tiffWriter;
        ImageWriteParam tiffWriteParam;
        IIOMetadata tiffStreamMetadata;
        IIOMetadata primaryIFD;
        BufferedImage image;
        BufferedImage thumbnail;

        // Specify uncompressed output.
        tiffWriteParam.setCompressionMode(ImageWriteParam.MODE_DISABLED);

        if (thumbnail != null) {
            // Write the TIFF header.
            tiffWriter.prepareWriteSequence(tiffStreamMetadata);

            // Append the primary IFD.
            tiffWriter.prepareInsertEmpty(-1, // append
                    new ImageTypeSpecifier(image),
                    image.getWidth(),
                    image.getHeight(),
                    primaryIFD,
                    null, // thumbnails
                    tiffWriteParam);
            tiffWriter.endInsertEmpty();

            // Append the thumbnail image data.
            tiffWriter.writeToSequence(new IIOImage(thumbnail, null, null),
                    tiffWriteParam);

            // Insert the primary image data.
            tiffWriter.prepareReplacePixels(0, new Rectangle(image.getWidth(),
                    image.getHeight()));
            tiffWriter.replacePixels(image, tiffWriteParam);
            tiffWriter.endReplacePixels();

            // End writing.
            tiffWriter.endWriteSequence();
        } else {
            // Write only the primary IFD and image data.
            tiffWriter.write(tiffStreamMetadata,
                    new IIOImage(image, null, primaryIFD),
                    tiffWriteParam);
        }

#### Writing Compressed Exif Images

The structure of the embedded TIFF stream in the `APP1` segment of a compressed Exif image is identical to the uncompressed Exif image structure except that there are no primary image data, i.e., the primary IFD does not refer to any image data.

        ImageWriter tiffWriter;
        ImageWriteParam tiffWriteParam;
        IIOMetadata tiffStreamMetadata;
        BufferedImage image;
        BufferedImage thumbnail;
        IIOMetadata primaryIFD;
        ImageOutputStream output;

        // Set up an output to contain the APP1 Exif TIFF stream.
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        MemoryCacheImageOutputStream app1ExifOutput =
            new MemoryCacheImageOutputStream(baos);
        tiffWriter.setOutput(app1ExifOutput);

        // Set compression for the thumbnail.
        tiffWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        tiffWriteParam.setCompressionType("Exif JPEG");

        // Write the APP1 Exif TIFF stream.
        if (thumbnail != null) {
            // Write the TIFF header.
            tiffWriter.prepareWriteSequence(tiffStreamMetadata);

            // Append the primary IFD.
            tiffWriter.prepareInsertEmpty(-1, // append
                    new ImageTypeSpecifier(image),
                    image.getWidth(),
                    image.getHeight(),
                    primaryIFD,
                    null, // thumbnails
                    tiffWriteParam);
            tiffWriter.endInsertEmpty();

            // Append the thumbnail IFD and image data.
            tiffWriter.writeToSequence(new IIOImage(thumbnail, null,
                    null), tiffWriteParam);

            // End writing.
            tiffWriter.endWriteSequence();
        } else {
            // Write only the primary IFD.
            tiffWriter.prepareWriteEmpty(tiffStreamMetadata,
                    new ImageTypeSpecifier(image),
                    image.getWidth(),
                    image.getHeight(),
                    primaryIFD,
                    null, // thumbnails
                    tiffWriteParam);
            tiffWriter.endWriteEmpty();
        }

        // Flush data into byte stream.
        app1ExifOutput.flush();

        // Create APP1 parameter array.
        byte[] app1Parameters = new byte[6 + baos.size()];

        // Add APP1 Exif ID bytes.
        app1Parameters[0] = (byte) 'E';
        app1Parameters[1] = (byte) 'x';
        app1Parameters[2] = (byte) 'i';
        app1Parameters[3] = (byte) 'f';
        app1Parameters[4] = app1Parameters[5] = (byte) 0;

        // Append TIFF stream to APP1 parameters.
        System.arraycopy(baos.toByteArray(), 0, app1Parameters, 6, baos.size());

        // Create the APP1 Exif node to be added to native JPEG image metadata.
        IIOMetadataNode app1Node = new IIOMetadataNode("unknown");
        app1Node.setAttribute("MarkerTag", String.valueOf(0xE1));
        app1Node.setUserObject(app1Parameters);

        // Append the APP1 Exif marker to the "markerSequence" node.
        IIOMetadata jpegImageMetadata =
            jpegWriter.getDefaultImageMetadata(new ImageTypeSpecifier(image),
                jpegWriteParam);
        String nativeFormat = jpegImageMetadata.getNativeMetadataFormatName();
        Node tree = jpegImageMetadata.getAsTree(nativeFormat);
        NodeList children = tree.getChildNodes();
        int numChildren = children.getLength();
        for (int i = 0; i < numChildren; i++) {
            Node child = children.item(i);
            if (child.getNodeName().equals("markerSequence")) {
                child.appendChild(app1Node);
                break;
            }
        }
        jpegImageMetadata.setFromTree(nativeFormat, tree);

        // Write the JPEG image data including the APP1 Exif marker.
        jpegWriter.setOutput(output);
        jpegWriter.write(new IIOImage(image, null, jpegImageMetadata));

The `"unknown"` node created above would be appended to the `"markerSequence"` node of the native JPEG image metadata and written to the JPEG stream when the primary image is written using the JPEG writer.

## Stream Metadata

The DTD for the TIFF native stream metadata format is as follows:

    <!DOCTYPE "javax_imageio_tiff_stream_1.0" [

      <!ELEMENT "javax_imageio_tiff_stream_1.0" (ByteOrder)>

        <!ELEMENT "ByteOrder" EMPTY>
          <!-- The stream byte order -->
          <!ATTLIST "ByteOrder" "value" #CDATA #REQUIRED>
            <!-- One of "BIG_ENDIAN" or "LITTLE_ENDIAN" -->
            <!-- Data type: String -->
    ]>

## Image Metadata

The DTD for the TIFF native image metadata format is as follows:

    <!DOCTYPE "javax_imageio_tiff_image_1.0" [

      <!ELEMENT "javax_imageio_tiff_image_1.0" (TIFFIFD)*>

        <!ELEMENT "TIFFIFD" (TIFFField | TIFFIFD)*>
          <!-- An IFD (directory) containing fields -->
          <!ATTLIST "TIFFIFD" "tagSets" #CDATA #REQUIRED>
            <!-- Data type: String -->
          <!ATTLIST "TIFFIFD" "parentTagNumber" #CDATA #IMPLIED>
            <!-- The tag number of the field pointing to this IFD -->
            <!-- Data type: Integer -->
          <!ATTLIST "TIFFIFD" "parentTagName" #CDATA #IMPLIED>
            <!-- A mnemonic name for the field pointing to this IFD, if known
                 -->
            <!-- Data type: String -->

          <!ELEMENT "TIFFField" (TIFFBytes | TIFFAsciis |
            TIFFShorts | TIFFSShorts | TIFFLongs | TIFFSLongs |
            TIFFRationals | TIFFSRationals |
            TIFFFloats | TIFFDoubles | TIFFUndefined)>
            <!-- A field containing data -->
            <!ATTLIST "TIFFField" "number" #CDATA #REQUIRED>
              <!-- The tag number associated with the field -->
              <!-- Data type: String -->
            <!ATTLIST "TIFFField" "name" #CDATA #IMPLIED>
              <!-- A mnemonic name associated with the field, if known -->
              <!-- Data type: String -->

            <!ELEMENT "TIFFBytes" (TIFFByte)*>
              <!-- A sequence of TIFFByte nodes -->

              <!ELEMENT "TIFFByte" EMPTY>
                <!-- An integral value between 0 and 255 -->
                <!ATTLIST "TIFFByte" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->
                <!ATTLIST "TIFFByte" "description" #CDATA #IMPLIED>
                  <!-- A description, if available -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFAsciis" (TIFFAscii)*>
              <!-- A sequence of TIFFAscii nodes -->

              <!ELEMENT "TIFFAscii" EMPTY>
                <!-- A String value -->
                <!ATTLIST "TIFFAscii" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFShorts" (TIFFShort)*>
              <!-- A sequence of TIFFShort nodes -->

              <!ELEMENT "TIFFShort" EMPTY>
                <!-- An integral value between 0 and 65535 -->
                <!ATTLIST "TIFFShort" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->
                <!ATTLIST "TIFFShort" "description" #CDATA #IMPLIED>
                  <!-- A description, if available -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFSShorts" (TIFFSShort)*>
              <!-- A sequence of TIFFSShort nodes -->

              <!ELEMENT "TIFFSShort" EMPTY>
                <!-- An integral value between -32768 and 32767 -->
                <!ATTLIST "TIFFSShort" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->
                <!ATTLIST "TIFFSShort" "description" #CDATA #IMPLIED>
                  <!-- A description, if available -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFLongs" (TIFFLong)*>
              <!-- A sequence of TIFFLong nodes -->

              <!ELEMENT "TIFFLong" EMPTY>
                <!-- An integral value between 0 and 4294967295 -->
                <!ATTLIST "TIFFLong" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->
                <!ATTLIST "TIFFLong" "description" #CDATA #IMPLIED>
                  <!-- A description, if available -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFSLongs" (TIFFSLong)*>
              <!-- A sequence of TIFFSLong nodes -->

              <!ELEMENT "TIFFSLong" EMPTY>
                <!-- An integral value between -2147483648 and 2147482647 -->
                <!ATTLIST "TIFFSLong" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->
                <!ATTLIST "TIFFSLong" "description" #CDATA #IMPLIED>
                  <!-- A description, if available -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFRationals" (TIFFRational)*>
              <!-- A sequence of TIFFRational nodes -->

              <!ELEMENT "TIFFRational" EMPTY>
                <!-- A rational value consisting of an unsigned numerator and
                     denominator -->
                <!ATTLIST "TIFFRational" "value" #CDATA #IMPLIED>
                  <!-- The numerator and denominator, separated by a slash -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFSRationals" (TIFFSRational)*>
              <!-- A sequence of TIFFSRational nodes -->

              <!ELEMENT "TIFFSRational" EMPTY>
                <!-- A rational value consisting of a signed numerator and
                     denominator -->
                <!ATTLIST "TIFFSRational" "value" #CDATA #IMPLIED>
                  <!-- The numerator and denominator, separated by a slash -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFFloats" (TIFFFloat)*>
              <!-- A sequence of TIFFFloat nodes -->

              <!ELEMENT "TIFFFloat" EMPTY>
                <!-- A single-precision floating-point value -->
                <!ATTLIST "TIFFFloat" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFDoubles" (TIFFDouble)*>
              <!-- A sequence of TIFFDouble nodes -->

              <!ELEMENT "TIFFDouble" EMPTY>
                <!-- A double-precision floating-point value -->
                <!ATTLIST "TIFFDouble" "value" #CDATA #IMPLIED>
                  <!-- The value -->
                  <!-- Data type: String -->

            <!ELEMENT "TIFFUndefined" EMPTY>
              <!-- Uninterpreted byte data -->
              <!ATTLIST "TIFFUndefined" "value" #CDATA #IMPLIED>
                <!-- A list of comma-separated byte values -->
                <!-- Data type: String -->
    ]>

Since:
  9