"DNG格式标准规范1.7.0.0版本详解及使用指南"

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The Digital Negative (DNG) Specification Version 1.7.0.0 is a document released by Adobe Inc. in June 2023, outlining the standard specifications for the DNG file format. This format is designed to provide a universal format for storing digital photographs, allowing for greater interoperability between different software and hardware platforms. The DNG format is based on the TIFF/EP standard and encompasses metadata, image data, and a range of options for encoding and storing image information. It offers a number of advantages over proprietary raw formats, including improved data integrity, increased flexibility, and greater long-term compatibility. Adobe Inc. holds the copyright for the DNG Specification and strictly prohibits reproduction or transmission of any part of the document without authorization. The company can be contacted at its headquarters in San Jose, CA, or through its website for more information on obtaining the document or licensing the DNG format for use in software applications. Overall, the DNG Specification Version 1.7.0.0 represents a significant step forward in standardizing how digital photographs are stored and managed, offering a comprehensive set of guidelines for developers and photographers alike. Its release marks an important milestone in the ongoing evolution of digital imaging technology, promoting open standards and ensuring the long-term viability of digital image archives.

Digital Negative Specification 1.7.0.0 June 2023

Depth information is stored as an 8 or 16-bit single channel unsigned integer image. Zero encodes the

“nearest distance” (closest to the camera), and the maximum possible unsigned integer encodes the

“farthest distance”. The mapping of the depth map integer values to distance values is specified by the

DepthFormat, DepthNear, DepthFar, DepthUnits, and DepthMeasureType tags.

The depth map should match the field of view of the main image. It may have a different pixel resolution

than the main image, but if the depth map is resized to match the size of the main image, the pixels should

correspond. The depth values should be filled in by an estimation algorithm for any areas of the depth map

that cannot be measured directly (i.e. no holes are allowed in depth maps).

Enhanced Image Data

DNG 1.5.0.0 adds the concept of enhanced image data, which is a more processed (and always at least

demosaiced) version of the raw image data.

Enhanced image data is stored in an IFD with a NewSubFileType of 16 (see section on NewSubFileType for

details).

The enhanced image data should always use a PhotometricInterpretation of 34892 (LinearRaw). It should use

the same color space as the raw image data.

The enhanced image data should use either 16-bit unsigned integer encoding, or 16 or 24 or 32-bit floating

point encoding.

The enhanced image data is assumed to have already been mapped to linear reference values, with the

exception that it may have a non-zero BlackLevel tag if unsigned integer encoding is used. This black level is

required to be the same for all color planes of the enhanced image data.

The enhanced IFD may have its own copies of the BaselineSharpness, NoiseProfile, and

NoiseReductionApplied tags, which may differ from the raw IFD versions of these tags due to sharpening or

noise reduction having been applied to the enhanced image data.

The enhanced IFD should have a non-null EnhanceParams tag to document the operations used to enhance

the image data.

Semantic Masks

DNG 1.6.0.0 and later supports the concept of "Semantic Masks" which may be used for purposes such as

image segmentation.

Semantic information is supported by allowing semantic masks (images) to be stored in IFDs with a

NewSubFileType of 65540 (10004.H). See section on NewSubFileType for details.

The semantic information IFD should use a PhotometricInterpretation of 52527 (CD2F.H). See section on

PhotometricInterpretation for details.

Semantic information is stored as a single channel image with one of the following pixel data types, with valid

encoding range indicated in parentheses:

• 8-bit unsigned integer (0 to 255)

• 16-bit unsigned integer (0 to 65535)

Digital Negative Specification 1.7.0.0 June 2023

Restrictions and Extensions to Existing TIFF Tags

This section describes the restrictions and extension to the following TIFF tags:

• NewSubFileType

• BitsPerSample

• SampleFormat

• Compression

• Predictor

• PhotometricInterpretation

• Orientation

NewSubFileType

In DNG versions earlier than 1.2.0.0, full resolution raw images should use NewSubFileType equal to 0.

Rendered previews or reduced resolution versions of raw images should use NewSubFileType equal to 1.

DNG 1.2.0.0 allows a new value for NewSubFileType equal to 10001.H.

This value, used for alternative or non-primary rendered previews, allows for multiple renderings (not just

multiple sizes of a single rendering) to be stored in a DNG file. DNG reading software that displays a preview

for a DNG file should, by default, display a preview from an IFD with NewSubFileType equal to 1. Alternative

renderings should only be displayed if requested by the user.

DNG 1.4.0.0 allows two new values for NewSubFileType. Transparency information for the full resolution raw

image should use NewSubFileType equal to 4. Transparency information for reduced resolution versions of

raw images should use NewSubFileType equal to 5.

DNG 1.5.0.0 allows three new values for NewSubFileType. Depth map information of the highest resolution

should use NewSubFileType equal to 8. Depth map information of lower resolutions should use a

NewSubFileType of 9. Enhanced image data should use a NewSubFileType equal to 16.

DNG 1.6.0.0 allows a new value of NewSubFileType. Semantic mask information should use NewSubFileType

equal to 65540 (10004.H). Multiple semantic masks can be stored in a DNG file.

BitsPerSample

Supported values are from 8 to 32 bits/sample. The depth must be the same for each sample if

SamplesPerPixel is not equal to 1. If BitsPerSample is not equal to 8 or 16 or 32, then the bits must be packed

into bytes using the TIFF default FillOrder of 1 (big-endian), even if the TIFF file itself uses little-endian byte

order.

SampleFormat

DNG versions earlier than 1.4.0.0 always use the default SampleFormat value of 1 (unsigned integer). DNG

version 1.4.0.0 allows an additional SampleFormat value of 3 (IEEE floating point). The allowed BitsPerSample

values for floating point images are 16, 24, and 32.

Compression

Two Compression tag values are supported in DNG versions before 1.4.0.0:

• Value = 1: Uncompressed data.

• Value = 7: JPEG compressed data, either baseline DCT JPEG, or lossless JPEG compression.

Digital Negative Specification 1.7.0.0 June 2023

If PhotometricInterpretation = 6 (YCbCr) and BitsPerSample = 8/8/8, or if PhotometricInterpretation = 1

(BlackIsZero) and BitsPerSample = 8, then the JPEG variant must be baseline DCT JPEG.

Otherwise, the JPEG variant must be lossless Huffman JPEG. For lossless JPEG, the internal

width/length/components in the JPEG stream are not required to match the strip or tile's

width/length/components. Only the total sample counts need to match. It is common for CFA images to be

encoded with a different width, length or component count to allow the JPEG compression predictors to

work across like colors.

DNG Version 1.4.0.0 adds support for the following compression codes:

• Value = 8: Deflate (ZIP)

• Value = 34892: Lossy JPEG

Deflate (8) compression is allowed for floating point image data, 32-bit integer image data, transparency

mask data, and depth map data.

Lossy JPEG (34892) is allowed for IFDs that use 8-bit integer data and one of the following

PhotometricInterpretation values:

• 34892 (LinearRaw)

• 52527 (PhotometricMask)

This compression code is required to let the DNG reader know to use a lossy JPEG decoder rather than a

lossless JPEG decoder for this combination of PhotometricInterpretation and BitsPerSample.

DNG Version 1.7.0.0 adds support for JPEG XL compression (see ISO/IEC 18181-1:2022):

• Value = 52546: JPEG XL

JPEG XL compression is allowed for N-bit integer image data, where 8 ≤ N ≤ 16, and 16-bit floating point

image data. The number of images planes must be either 1 or 3. The PhotometricInterpretation must be one

of the following values:

• 0 (piWhiteIsZero)

• 1 (piBlackIsZero)

• 2 (piRGB)

• 4 (piTransparencyMask)

• 34892 (LinearRaw)

• 51177 (Depth)

• 52527 (PhotometricMask)

JPEG XL supports two types of bitstreams:

• A “bare” format with no metadata

• A “container” format that uses the ISO Base Media File Format box structure with optional metadata

Both types of JPEG XL bitstreams are supported in DNG.

When using JPEG XL with multiple tiles, it is recommended to use the bare format, because each compressed

tile will be slightly smaller, and per-tile metadata is not required.

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