Class PelTag

Description

Class with static methods for EXIF tags.

This class defines the constants that represents the EXIF tags known to PEL. They are supposed to be used whenever one needs to specify an EXIF tag, and they will be denoted by the pseudo type PelTag throughout the documentation.

All the methods in this class are static and should be called with the EXIF tag on which they should operate.

Located in /PelTag.php (line 57)


	
			
Class Constant Summary
 APERTURE_VALUE = 0x9202
 ARTIST = 0x013B
 BATTERY_LEVEL = 0x828F
 BITS_PER_SAMPLE = 0x0102
 BRIGHTNESS_VALUE = 0x9203
 CFA_PATTERN = 0x828E
 COLOR_SPACE = 0xA001
 COMPRESSION = 0x0103
 CONTRAST = 0xA408
 COPYRIGHT = 0x8298
 CUSTOM_RENDERED = 0xA401
 DATE_TIME = 0x0132
 DOCUMENT_NAME = 0x010D
 EXIF_IFD_POINTER = 0x8769
 EXIF_VERSION = 0x9000
 EXPOSURE_INDEX = 0xA215
 EXPOSURE_MODE = 0xA402
 EXPOSURE_PROGRAM = 0x8822
 EXPOSURE_TIME = 0x829A
 FILE_SOURCE = 0xA300
 FILL_ORDER = 0x010A
 FLASH = 0x9209
 FLASH_ENERGY = 0xA20B
 FNUMBER = 0x829D
 FOCAL_LENGTH = 0x920A
 GAIN_CONTROL = 0xA407
 IMAGE_LENGTH = 0x0101
 IMAGE_UNIQUE_ID = 0xA420
 IMAGE_WIDTH = 0x0100
 IPTC_NAA = 0x83BB
 JPEG_PROC = 0x0200
 LIGHT_SOURCE = 0x9208
 MAKE = 0x010F
 MAKER_NOTE = 0x927C
 METERING_MODE = 0x9207
 MODEL = 0x0110
 NEW_CFA_PATTERN = 0xA302
 OECF = 0x8828
 ORIENTATION = 0x0112
 RESOLUTION_UNIT = 0x0128
 ROWS_PER_STRIP = 0x0116
 SATURATION = 0xA409
 SCENE_TYPE = 0xA301
 SENSING_METHOD = 0xA217
 SHARPNESS = 0xA40A
 SOFTWARE = 0x0131
 STRIP_OFFSETS = 0x0111
 SUBJECT_AREA = 0x9214
 SUBJECT_DISTANCE = 0x9206
 SUBJECT_LOCATION = 0xA214
 SUB_SEC_TIME = 0x9290
 TRANSFER_RANGE = 0x0156
 USER_COMMENT = 0x9286
 WHITE_BALANCE = 0xA403
 WHITE_POINT = 0x013E
 X_RESOLUTION = 0x011A
 Y_RESOLUTION = 0x011B
Method Summary
 string getDescription (PelTag $tag)
 string getName (PelTag $tag)
 string getTitle (PelTag $tag)
 boolean isKnownTag (PelTag $tag)
Methods
getDescription (line 1483)

Returns a description of an EXIF tag.

  • return: the description of the tag which generally explains how the tag is supposed to be used or interpreted. If the tag isn't known, the string 'Unknown Tag :0xTT' will be returned where 'TT' is the hexadecimal representation of the tag.
string getDescription (PelTag $tag)
getName (line 1015)

Returns a short name for an EXIF tag.

  • return: the short name of the tag, e.g., 'ImageWidth' for the IMAGE_WIDTH tag. If the tag isn't known, the string 'Unknown:0xTT' will be returned where 'TT' is the hexadecimal representation of the tag.
  • static:
string getName (PelTag $tag)
getTitle (line 1249)

Returns a title for an EXIF tag.

  • return: the title of the tag, e.g., 'Image Width' for the IMAGE_WIDTH tag. If the tag isn't known, the string 'Unknown Tag: 0xTT' will be returned where 'TT' is the hexadecimal representation of the tag.
string getTitle (PelTag $tag)
isKnownTag (line 1000)

Check a short value to see if it's a valid EXIF tag.

  • return: true if the tag is known, false otherwise.
  • static:
boolean isKnownTag (PelTag $tag)
Class Constants
APERTURE_VALUE = 0x9202 (line 561)

Aperture

The lens aperture. The unit is the APEX value.

ARTIST = 0x013B (line 277)

Artist

This tag records the name of the camera owner, photographer or image creator. The detailed format is not specified, but it is recommended that the information be written as in the example below for ease of Interoperability. When the field is left blank, it is treated as unknown.

BATTERY_LEVEL = 0x828F (line 400)

Battery Level

BITS_PER_SAMPLE = 0x0102 (line 98)

Bits per Sample

The number of bits per image component. In this standard each component of the image is 8 bits, so the value for this tag is 9. See also SAMPLES_PER_PIXEL. In JPEG compressed data a JPEG marker is used instead of this tag.

BRIGHTNESS_VALUE = 0x9203 (line 569)

Brightness

The value of brightness. The unit is the APEX value. Ordinarily it is given in the range of -99.99 to 99.99.

CFA_PATTERN = 0x828E (line 397)

CFA Pattern

Indicates the color filter array (CFA) geometric pattern of the image sensor when a one-chip color area sensor is used. It does not apply to all sensing methods.

CFA_REPEAT_PATTERN_DIM = 0x828D (line 388)

CFA Repeat Pattern Dim

COLOR_SPACE = 0xA001 (line 711)

Color Space

The color space information tag is always recorded as the color space specifier. Normally sRGB (=1) is used to define the color space based on the PC monitor conditions and environment. If a color space other than sRGB is used, Uncalibrated (=FFFF.H) is set. Image data recorded as Uncalibrated can be treated as sRGB when it is converted to FlashPix. On sRGB see Appendix E.

COMPONENTS_CONFIGURATION = 0x9101 (line 537)

Components Configuration

Information specific to compressed data. The channels of each component are arranged in order from the 1st component to the 4th. For uncompressed data the data arrangement is given in the PHOTOMETRIC_INTERPRETATION tag. However, since PHOTOMETRIC_INTERPRETATION can only express the order of Y, Cb and Cr, this tag is provided for cases when compressed data uses components other than Y, Cb, and Cr and to enable support of other sequences.

COMPRESSED_BITS_PER_PIXEL = 0x9102 (line 546)

Compressed Bits per Pixel

Information specific to compressed data. The compression mode used for a compressed image is indicated in unit bits per pixel.

COMPRESSION = 0x0103 (line 108)

Compression

The compression scheme used for the image data. When a primary image is JPEG compressed, this designation is not necessary and is omitted. When thumbnails use JPEG compression, this tag value is set to 6.

CONTRAST = 0xA408 (line 949)

Contrast

This tag indicates the direction of contrast processing applied by the camera when the image was shot.

COPYRIGHT = 0x8298 (line 425)

Copyright

Copyright information. In this standard the tag is used to indicate both the photographer and editor copyrights. It is the copyright notice of the person or organization claiming rights to the image. The Interoperability copyright statement including date and rights should be written in this field; e.g., "Copyright, John Smith, 19xx. All rights reserved.". In this standard the field records both the photographer and editor copyrights, with each recorded in a separate part of the statement. When there is a clear distinction between the photographer and editor copyrights, these are to be written in the order of photographer followed by editor copyright, separated by NULL (in this case, since the statement also ends with a NULL, there are two NULL codes) (see example 1). When only the photographer is given, it is terminated by one NULL code (see example 2). When only the editor copyright is given, the photographer copyright part consists of one space followed by a terminating NULL code, then the editor copyright is given (see example 3). When the field is left blank, it is treated as unknown.

CUSTOM_RENDERED = 0xA401 (line 888)

Custom Rendered

This tag indicates the use of special processing on image data, such as rendering geared to output. When special processing is performed, the reader is expected to disable or minimize any further processing.

DATE_TIME = 0x0132 (line 266)

Date and Time

The date and time of image creation. In this standard (EXIF-2.1) it is the date and time the file was changed.

DATE_TIME_DIGITIZED = 0x9004 (line 523)

Date and Time (digitized)

The date and time when the image was stored as digital data.

DATE_TIME_ORIGINAL = 0x9003 (line 515)

Date and Time (original)

The date and time when the original image data was generated. For a digital still camera the date and time the picture was taken are recorded.

DEVICE_SETTING_DESCRIPTION = 0xA40B (line 974)

Device Setting Description

This tag indicates information on the picture-taking conditions of a particular camera model. The tag is used only to indicate the picture-taking conditions in the reader.

DIGITAL_ZOOM_RATIO = 0xA404 (line 914)

Digital Zoom Ratio

This tag indicates the digital zoom ratio when the image was shot. If the numerator of the recorded value is 0, this indicates that digital zoom was not used.

DOCUMENT_NAME = 0x010D (line 122)

Document Name

EXIF_IFD_POINTER = 0x8769 (line 452)

Exif IFD Pointer

A pointer to the Exif IFD. Interoperability, Exif IFD has the same structure as that of the IFD specified in TIFF. ordinarily, however, it does not contain image data as in the case of TIFF.

EXIF_VERSION = 0x9000 (line 506)

Exif Version

The version of this standard supported. Nonexistence of this field is taken to mean non-conformance to the standard.

EXPOSURE_BIAS_VALUE = 0x9204 (line 577)

Exposure Bias

The exposure bias. The units is the APEX value. Ordinarily it is given in the range of -99.99 to 99.99.

EXPOSURE_INDEX = 0xA215 (line 843)

Exposure index

Indicates the exposure index selected on the camera or input device at the time the image is captured.

EXPOSURE_MODE = 0xA402 (line 897)

Exposure Mode

This tag indicates the exposure mode set when the image was shot. In auto-bracketing mode, the camera shoots a series of frames of the same scene at different exposure settings.

EXPOSURE_PROGRAM = 0x8822 (line 463)

Exposure Program

The class of the program used by the camera to set exposure when the picture is taken.

EXPOSURE_TIME = 0x829A (line 432)

Exposure Time

Exposure time, given in seconds (sec).

FILE_SOURCE = 0xA300 (line 860)

File Source

Indicates the image source. If a DSC recorded the image, this tag value of this tag always be set to 3, indicating that the image was recorded on a DSC.

FILL_ORDER = 0x010A (line 119)

Fill Order

FLASH = 0x9209 (line 615)

Flash

This tag is recorded when an image is taken using a strobe light (flash).

FLASH_ENERGY = 0xA20B (line 788)

Flash Energy

Indicates the strobe energy at the time the image is captured, as measured in Beam Candle Power Seconds (BCPS).

FLASH_PIX_VERSION = 0xA000 (line 699)

FlashPix Version

The FlashPix format version supported by a FPXR file.

FNUMBER = 0x829D (line 439)

FNumber

The F number.

FOCAL_LENGTH = 0x920A (line 624)

Focal Length

The actual focal length of the lens, in mm. Conversion is not made to the focal length of a 35 mm film camera, see the FOCAL_LENGTH_IN_35MM_FILM tag for this information.

FOCAL_LENGTH_IN_35MM_FILM = 0xA405 (line 924)

Focal Length In 35mm Film

This tag indicates the equivalent focal length assuming a 35mm film camera, in mm. A value of 0 means the focal length is unknown. Note that this tag differs from the FOCAL_LENGTH tag.

FOCAL_PLANE_RESOLUTION_UNIT = 0xA210 (line 824)

Focal Plane Resolution Unit

Indicates the unit for measuring FOCAL_PLANE_X_RESOLUTION and FOCAL_PLANE_Y_RESOLUTION. This value is the same as the RESOLUTION_UNIT.

FOCAL_PLANE_X_RESOLUTION = 0xA20E (line 806)

Focal Plane x-Resolution

Indicates the number of pixels in the image width (X) direction per FOCAL_PLANE_RESOLUTION_UNIT on the camera focal plane.

FOCAL_PLANE_Y_RESOLUTION = 0xA20F (line 815)

Focal Plane y-Resolution

Indicates the number of pixels in the image height (V) direction per FOCAL_PLANE_RESOLUTION_UNIT on the camera focal plane.

GAIN_CONTROL = 0xA407 (line 941)

Gain Control

This tag indicates the degree of overall image gain adjustment.

GPS_INFO_IFD_POINTER = 0x8825 (line 481)

GPS Info IFD Pointer

A pointer to the GPS Info IFD. The Interoperability structure of the GPS Info IFD, like that of Exif IFD, has no image data.

IMAGE_DESCRIPTION = 0x010E (line 132)

Image Description

A character string giving the title of the image. It may be a comment such as "1988 company picnic" or the like. Two-bytes character codes cannot be used. When a 2-bytes code is necessary, the Exif Private tag USER_COMMENT is to be used.

IMAGE_LENGTH = 0x0101 (line 88)

Image Length

The number of rows of image data. In JPEG compressed data a JPEG marker is used instead of this tag.

IMAGE_UNIQUE_ID = 0xA420 (line 990)

Image Unique ID

This tag indicates an identifier assigned uniquely to each image. It is recorded as an ASCII string equivalent to hexadecimal notation and 128-bit fixed length.

IMAGE_WIDTH = 0x0100 (line 80)

Image Width

The number of columns of image data, equal to the number of pixels per row. In JPEG compressed data a JPEG marker is used instead of this tag.

INTEROPERABILITY_IFD_POINTER = 0xA005 (line 780)

Interoperability IFD Pointer

Interoperability IFD is composed of tags which stores the information to ensure the Interoperability and pointed by the following tag located in Exif IFD. The Interoperability structure of Interoperability IFD is the same as TIFF defined IFD structure but does not contain the image data characteristically compared with normal TIFF IFD.

INTEROPERABILITY_INDEX = 0x0001 (line 68)

Interoperability Index

Indicates the identification of the Interoperability rule. Use "R98" for stating ExifR98 Rules. Four bytes used including the termination code (NULL). see the separate volume of Recommended Exif Interoperability Rules (ExifR98) for other tags used for ExifR98.

INTEROPERABILITY_VERSION = 0x0002 (line 71)

Interoperability Version

INTER_COLOR_PROFILE = 0x8773 (line 455)

Inter Color Profile

IPTC_NAA = 0x83BB (line 442)

IPTC/NAA

ISO_SPEED_RATINGS = 0x8827 (line 489)

ISO Speed Ratings

Indicates the ISO Speed and ISO Latitude of the camera or input device as specified in ISO 12232.

JPEG_INTERCHANGE_FORMAT = 0x0201 (line 310)

JPEG Interchange Format

The offset to the start byte (SOI) of JPEG compressed thumbnail data. This is not used for primary image JPEG data.

JPEG_INTERCHANGE_FORMAT_LENGTH = 0x0202 (line 324)

JPEG Interchange Format Length

The number of bytes of JPEG compressed thumbnail data. This is not used for primary image JPEG data. JPEG thumbnails are not divided but are recorded as a continuous JPEG bitstream from SOI to EOI. Appn and COM markers should not be recorded. Compressed thumbnails must be recorded in no more than 64 Kbytes, including all other data to be recorded in APP1.

JPEG_PROC = 0x0200 (line 301)

JPEGProc

LIGHT_SOURCE = 0x9208 (line 607)

Light Source

The kind of light source.

MAKE = 0x010F (line 142)

Manufacturer

The manufacturer of the recording equipment. This is the manufacturer of the DSC, scanner, video digitizer or other equipment that generated the image. When the field is left blank, it is treated as unknown.

MAKER_NOTE = 0x927C (line 640)

Maker Note

A tag for manufacturers of Exif writers to record any desired information. The contents are up to the manufacturer.

MAX_APERTURE_VALUE = 0x9205 (line 586)

Max Aperture Value

The smallest F number of the lens. The unit is the APEX value. Ordinarily it is given in the range of 00.00 to 99.99, but it is not limited to this range.

METERING_MODE = 0x9207 (line 600)

Metering Mode

The metering mode.

MODEL = 0x0110 (line 152)

Model

The model name or model number of the equipment. This is the model name or number of the DSC, scanner, video digitizer or other equipment that generated the image. When the field is left blank, it is treated as unknown.

NEW_CFA_PATTERN = 0xA302 (line 878)

CFA Pattern

Indicates the color filter array (CFA) geometric pattern of the image sensor when a one-chip color area sensor is used. It does not apply to all sensing methods.

OECF = 0x8828 (line 498)

OECF

Indicates the Opto-Electoric Conversion Function (OECF) specified in ISO 14524. OECF is the relationship between the camera optical input and the image values.

ORIENTATION = 0x0112 (line 170)

Orientation

The image orientation viewed in terms of rows and columns.

PHOTOMETRIC_INTERPRETATION = 0x0106 (line 116)

Photometric Interpretation

The pixel composition. In JPEG compressed data a JPEG marker is used instead of this tag.

PIXEL_X_DIMENSION = 0xA002 (line 722)

Pixel x-Dimension

Information specific to compressed data. When a compressed file is recorded, the valid width of the meaningful image must be recorded in this tag, whether or not there is padding data or a restart marker. This tag should not exist in an uncompressed file. For details see section 2.8.1 and Appendix F.

PIXEL_Y_DIMENSION = 0xA003 (line 736)

Pixel y-Dimension

Information specific to compressed data. When a compressed file is recorded, the valid height of the meaningful image must be recorded in this tag, whether or not there is padding data or a restart marker. This tag should not exist in an uncompressed file. For details see section 2.8.1 and Appendix F. Since data padding is unnecessary in the vertical direction, the number of lines recorded in this valid image height tag will in fact be the same as that recorded in the SOF.

PLANAR_CONFIGURATION = 0x011C (line 227)

Planar Configuration

Indicates whether pixel components are recorded in a chunky or planar format. In JPEG compressed files a JPEG marker is used instead of this tag. If this field does not exist, the TIFF default of 1 (chunky) is assumed.

PRIMARY_CHROMATICITIES = 0x013F (line 295)

Primary Chromaticities

The chromaticity of the three primary colors of the image. Normally this tag is not necessary, since colorspace is specified in the colorspace information tag (COLOR_SPACE).

REFERENCE_BLACK_WHITE = 0x0214 (line 376)

Reference Black/White

The reference black point value and reference white point value. No defaults are given in TIFF, but the values below are given as defaults here. The color space is declared in a color space information tag, with the default being the value that gives the optimal image characteristics Interoperability these conditions.

RELATED_IMAGE_FILE_FORMAT = 0x1000 (line 379)

Related Image File Format

RELATED_IMAGE_LENGTH = 0x1002 (line 385)

Related Image Length

RELATED_IMAGE_WIDTH = 0x1001 (line 382)

Related Image Width

RELATED_SOUND_FILE = 0xA004 (line 768)

Related Sound File

This tag is used to record the name of an audio file related to the image data. The only relational information recorded here is the Exif audio file name and extension (an ASCII string consisting of 8 characters + '.' + 3 characters). The path is not recorded. Stipulations on audio are given in section 3.6.3. File naming conventions are given in section 3.7.1. When using this tag, audio files must be recorded in conformance to the Exif audio format. Writers are also allowed to store the data such as Audio within APP2 as FlashPix extension stream data. Audio files must be recorded in conformance to the Exif audio format. The mapping of Exif image files and audio files is done in any of the three ways shown in Table 8. If multiple files are mapped to one file as in [2] or [3] of this table, the above format is used to record just one audio file name. If there are multiple audio files, the first recorded file is given. In the case of [3] in Table 8, for example, for the Exif image file "DSC00001.JPG" only "SND00001.WAV" is given as the related Exif audio file. When there are three Exif audio files "SND00001.WAV", "SND00002.WAV" and "SND00003.WAV", the Exif image file name for each of them, "DSC00001.JPG", is indicated. By combining multiple relational information, a variety of playback possibilities can be supported. The method of using relational information is left to the implementation on the playback side. Since this information is an ASCII character string, it is terminated by NULL. When this tag is used to map audio files, the relation of the audio file to image data must also be indicated on the audio file end.

RESOLUTION_UNIT = 0x0128 (line 237)

Resolution Unit

The unit for measuring X_RESOLUTION and Y_RESOLUTION. The same unit is used for both X_RESOLUTION and Y_RESOLUTION. If the image resolution is unknown, 2 (inches) is designated.

ROWS_PER_STRIP = 0x0116 (line 191)

Rows per Strip

The number of rows per strip. This is the number of rows in the image of one strip when an image is divided into strips. With JPEG compressed data this designation is not needed and is omitted. See also ROWS_PER_STRIP and STRIP_BYTE_COUNTS.

SAMPLES_PER_PIXEL = 0x0115 (line 180)

Samples per Pixel

The number of components per pixel. Since this standard applies to RGB and YCbCr images, the value set for this tag is 3. In JPEG compressed data a JPEG marker is used instead of this tag.

SATURATION = 0xA409 (line 957)

Saturation

This tag indicates the direction of saturation processing applied by the camera when the image was shot.

SCENE_CAPTURE_TYPE = 0xA406 (line 933)

Scene Capture Type

This tag indicates the type of scene that was shot. It can also be used to record the mode in which the image was shot. Note that this differs from the SCENE_TYPE tag.

SCENE_TYPE = 0xA301 (line 869)

Scene Type

Indicates the type of scene. If a DSC recorded the image, this tag value must always be set to 1, indicating that the image was directly photographed.

SENSING_METHOD = 0xA217 (line 851)

Sensing Method

Indicates the image sensor type on the camera or input device.

SHARPNESS = 0xA40A (line 965)

Sharpness

This tag indicates the direction of sharpness processing applied by the camera when the image was shot.

SHUTTER_SPEED_VALUE = 0x9201 (line 554)

Shutter speed

Shutter speed. The unit is the APEX (Additive System of Photographic Exposure) setting (see Appendix C).

SOFTWARE = 0x0131 (line 258)

Software

This tag records the name and version of the software or firmware of the camera or image input device used to generate the image. The detailed format is not specified, but it is recommended that the example shown below be followed. When the field is left blank, it is treated as unknown.

SPATIAL_FREQUENCY_RESPONSE = 0xA20C (line 797)

Spatial Frequency Response

This tag records the camera or input device spatial frequency table and SFR values in the direction of image width, image height, and diagonal direction, as specified in ISO 12233.

SPECTRAL_SENSITIVITY = 0x8824 (line 472)

Spectral Sensitivity

Indicates the spectral sensitivity of each channel of the camera used. The tag value is an ASCII string compatible with the standard developed by the ASTM Technical committee.

STRIP_BYTE_COUNTS = 0x0117 (line 199)

Strip Byte Count

The total number of bytes in each strip. With JPEG compressed data this designation is not needed and is omitted.

STRIP_OFFSETS = 0x0111 (line 163)

Strip Offsets

For each strip, the byte offset of that strip. It is recommended that this be selected so the number of strip bytes does not exceed 64 Kbytes. With JPEG compressed data this designation is not needed and is omitted. See also ROWS_PER_STRIP and STRIP_BYTE_COUNTS.

SUBJECT_AREA = 0x9214 (line 632)

Subject Area

This tag indicates the location and area of the main subject in the overall scene.

SUBJECT_DISTANCE = 0x9206 (line 593)

Subject Distance

The distance to the subject, given in meters.

SUBJECT_DISTANCE_RANGE = 0xA40C (line 981)

Subject Distance Range

This tag indicates the distance to the subject.

SUBJECT_LOCATION = 0xA214 (line 835)

Subject Location

Indicates the location of the main subject in the scene. The value of this tag represents the pixel at the center of the main subject relative to the left edge, prior to rotation processing as per the ROTATION tag. The first value indicates the X column number and second indicates the Y row number.

SUB_SEC_TIME = 0x9290 (line 676)

Subsec Time

A tag used to record fractions of seconds for the DATE_TIME tag.

SUB_SEC_TIME_DIGITIZED = 0x9292 (line 692)

SubSec Time Digitized

A tag used to record fractions of seconds for the DATE_TIME_DIGITIZED tag.

SUB_SEC_TIME_ORIGINAL = 0x9291 (line 684)

SubSec Time Original

A tag used to record fractions of seconds for the DATE_TIME_ORIGINAL tag.

TRANSFER_FUNCTION = 0x012D (line 247)

Transfer Function

A transfer function for the image, described in tabular style. Normally this tag is not necessary, since color space is specified in the color space information tag (COLOR_SPACE).

TRANSFER_RANGE = 0x0156 (line 298)

Transfer Range

USER_COMMENT = 0x9286 (line 668)

User Comment

A tag for Exif users to write keywords or comments on the image besides those in IMAGE_DESCRIPTION, and without the character code limitations of the IMAGE_DESCRIPTION tag. The character code used in the USER_COMMENT tag is identified based on an ID code in a fixed 8-byte area at the start of the tag data area. The unused portion of the area is padded with NULL ("00.h"). ID codes are assigned by means of registration. The designation method and references for each character code are given in Table 6. The value of CountN is determined based on the 8 bytes in the character code area and the number of bytes in the user comment part. Since the TYPE is not ASCII, NULL termination is not necessary (see Fig. 9). The ID code for the USER_COMMENT area may be a Defined code such as JIS or ASCII, or may be Undefined. The Undefined name is UndefinedText, and the ID code is filled with 8 bytes of all "NULL" ("00.H"). An Exif reader that reads the USER_COMMENT tag must have a function for determining the ID code. This function is not required in Exif readers that do not use the USER_COMMENT tag (see Table 7). When a USER_COMMENT area is set aside, it is recommended that the ID code be ASCII and that the following user comment part be filled with blank characters [20.H].

WHITE_BALANCE = 0xA403 (line 905)

White Balance

This tag indicates the white balance mode set when the image was shot.

WHITE_POINT = 0x013E (line 286)

White Point

The chromaticity of the white point of the image. Normally this tag is not necessary, since color space is specified in the colorspace information tag (COLOR_SPACE).

X_RESOLUTION = 0x011A (line 208)

x-Resolution

The number of pixels per RESOLUTION_UNIT in the IMAGE_WIDTH direction. When the image resolution is unknown, 72 [dpi] is designated.

YCBCR_COEFFICIENTS = 0x0211 (line 336)

YCbCr Coefficients

The matrix coefficients for transformation from RGB to YCbCr image data. No default is given in TIFF; but here the value given in Appendix E, "Color Space Guidelines", is used as the default. The color space is declared in a color space information tag, with the default being the value that gives the optimal image characteristics Interoperability this condition.

YCBCR_POSITIONING = 0x0213 (line 364)

YCbCr Positioning

The position of chrominance components in relation to the luminance component. This field is designated only for JPEG compressed data or uncompressed YCbCr data. The TIFF default is 1 (centered); but when Y:Cb:Cr = 4:2:2 it is recommended in this standard that 2 (co-sited) be used to record data, in order to improve the image quality when viewed on TV systems. When this field does not exist, the reader shall assume the TIFF default. In the case of Y:Cb:Cr = 4:2:0, the TIFF default (centered) is recommended. If the reader does not have the capability of supporting both kinds of YCB_CR_POSITIONING, it shall follow the TIFF default regardless of the value in this field. It is preferable that readers be able to support both centered and co-sited positioning.

YCBCR_SUB_SAMPLING = 0x0212 (line 345)

YCbCr Sub-Sampling

The sampling ratio of chrominance components in relation to the luminance component. In JPEG compressed data a JPEG marker is used instead of this tag.

Y_RESOLUTION = 0x011B (line 217)

y-Resolution

The number of pixels per RESOLUTION_UNIT in the IMAGE_LENGTH direction. The same value as X_RESOLUTION is designated.

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