OpenEXR attribute types

Each attribute in the header names a type, which decides how its value bytes are laid out. In the tables, int is 4 bytes, unsigned int is 4 bytes, float is 4 bytes, double is 8 bytes and unsigned long is 8 bytes, all little-endian.

Predefined types

Type	Layout
`box2i`	4 × int: xMin, yMin, xMax, yMax
`box2f`	4 × float: xMin, yMin, xMax, yMax
`bytes`	A sequence of bytes, with an optional type hint (new in version 3.4)
`chlist`	The channel entries below, then a zero byte
`chromaticities`	8 × float: redX, redY, greenX, greenY, blueX, blueY, whiteX, whiteY
`compression`	1 byte: a code below
`double`	double
`envmap`	1 byte: 0 is `ENVMAP_LATLONG`, 1 is `ENVMAP_CUBE`
`float`	float
`int`	int
`keycode`	7 × int: filmMfcCode, filmType, prefix, count, perfOffset, perfsPerFrame, perfsPerCount
`lineOrder`	1 byte: a code below
`m33f`	9 × float
`m44f`	16 × float
`preview`	2 × unsigned int (width, height), then width × height × 4 bytes of red, green, blue and alpha, top to bottom and left to right
`rational`	int, then unsigned int
`string`	int length, then that many characters
`stringvector`	Zero or more strings, each an int length and its characters. The count comes from the attribute size.
`tiledesc`	2 × unsigned int (xSize, ySize), then 1 byte: levelMode + roundingMode × 16
`timecode`	2 × unsigned int: timeAndFlags, userData
`v2i`, `v3i`	2 or 3 × int
`v2f`, `v3f`	2 or 3 × float

Channel list

A chlist value is a list of these entries, ended by a zero byte:

Field	Type	Description
Name	zero-terminated text	1 to 255 bytes.
Pixel type	int	A code below.
pLinear	1 byte	0 or 1.
Reserved	3 bytes	Zero.
xSampling	int	Horizontal sampling rate.
ySampling	int	Vertical sampling rate.

Pixel type	Value	Bytes per sample
`UINT`	0	4
`HALF`	1	2
`FLOAT`	2	4

Compression codes

Name	Value	Method
`NO_COMPRESSION`	0	None.
`RLE_COMPRESSION`	1	Lossless run-length encoding.
`ZIPS_COMPRESSION`	2	Lossless deflate, one scan line at a time.
`ZIP_COMPRESSION`	3	Lossless deflate on blocks of 16 scan lines.
`PIZ_COMPRESSION`	4	Lossless wavelet and Huffman coding, good for grainy images.
`PXR24_COMPRESSION`	5	Reduces 32-bit floats to 24 bits, then deflates. Lossless for `HALF` and `UINT`; slightly lossy for `FLOAT`.
`B44_COMPRESSION`	6	Lossy for `HALF` in 4 by 4 blocks. `UINT` and `FLOAT` are stored uncompressed.
`B44A_COMPRESSION`	7	As B44, with extra compression for flat areas such as alpha channels.
`DWAA_COMPRESSION`	8	Lossy, JPEG-like, on 32 scan lines, for RGB data.
`DWAB_COMPRESSION`	9	Lossy, JPEG-like, on 256 scan lines, for RGB data.
`HTJ2K256_COMPRESSION`	10	Lossless High-Throughput JPEG 2000 on 256 scan lines, for `HALF`, `FLOAT` and `UINT`.
`HTJ2K32_COMPRESSION`	11	Lossless High-Throughput JPEG 2000 on 32 scan lines, for `HALF`, `FLOAT` and `UINT`.

The chunks page lists the lines per block. PXR24, B44 and B44A are not used in deep files.

Other codes

Field	Name	Value
lineOrder	`INCREASING_Y`	0
lineOrder	`DECREASING_Y`	1
lineOrder	`RANDOM_Y`	2
tiledesc levelMode	`ONE_LEVEL`	0
tiledesc levelMode	`MIPMAP_LEVELS`	1
tiledesc levelMode	`RIPMAP_LEVELS`	2
tiledesc roundingMode	`ROUND_DOWN`	0
tiledesc roundingMode	`ROUND_UP`	1

Standard optional attributes

Applications can add attributes of their own. The OpenEXR project lists these as the standard optional attributes.

Name	Type	Meaning
`originalDataWindow`	box2i	Data window of the original image, kept when software crops it.
`worldToCamera`	m44f	Matrix from world space to the renderer’s camera space.
`worldToNDC`	m44f	Matrix from world space to normalised device coordinates.
`sensorCenterOffset`	v2f	Offset in microns of the sensor centre from the lens mount centre.
`sensorOverallDimensions`	v2f	Size of the sensor’s light-sensitive area, in millimetres.
`sensorPhotositePitch`	float	Distance between photosite centres, in microns.
`sensorAcquisitionRectangle`	box2i	Sensor area that corresponds to the captured pixels.
`xDensity`	float	Horizontal output density in pixels per inch.
`longitude`, `latitude`, `altitude`	float	Recording location: east of Greenwich, north of the equator, and metres above sea level.
`cameraMake`, `cameraModel`, `cameraSerialNumber`, `cameraFirmwareVersion`, `cameraUuid`, `cameraLabel`	string	Camera identification and a label for how it was used.
`cameraCCTSetting`, `cameraTintSetting`	float	Configured colour temperature in Kelvin and green or magenta tint.
`cameraColorBalance`	v2f	CIE 1960 UCS chromaticity treated as neutral.
`isoSpeed`, `expTime`, `shutterAngle`	float	ISO setting, exposure time in seconds and shutter angle in degrees.
`captureRate`	rational	Capture rate in frames per second.
`lensMake`, `lensModel`, `lensSerialNumber`, `lensFirmwareVersion`	string	Lens identification.
`nominalFocalLength`, `pinholeFocalLength`, `effectiveFocalLength`	float	Focal length in millimetres: as printed on the lens, in the pinhole model, and for a thick lens.
`entrancePupilOffset`	float	Axial distance from the image plane to the entrance pupil, in millimetres; can be negative.
`aperture`, `tStop`	float	The lens f-number, and the transmittance-corrected value.
`focus`	float	Focus distance in metres.
`owner`, `comments`	string	The image owner’s name, and a description.
`capDate`	string	Capture date in local time, `YYYY:MM:DD hh:mm:ss`.
`utcOffset`	float	Offset in seconds between UTC and local time.
`keyCode`	keycode	Film manufacturer, type, roll and frame position.
`framesPerSecond`	rational	Nominal playback frame rate; 24 if absent.
`timeCode`	timecode	Time and control code.
`imageCounter`	int	Image number giving the intended play order.
`reelName`	string	Name for a sequence of unique images.
`ascFramingDecisionList`	string	JSON-encoded ASC-FDL framing decisions.
`chromaticities`	chromaticities	CIE xy of the RGB primaries and white point; largely replaced by `colorInteropID`.
`colorInteropID`	string	Identifier for the RGB colour space (new in version 3.4).
`whiteLuminance`	float	Luminance, in nits, of RGB (1, 1, 1).
`adoptedNeutral`	v2f	CIE xy chromaticity to render as neutral on a display.
`acesImageContainerFlag`	int	1 means the file follows the SMPTE ST 2065-4 ACES layout.
`envmap`	envmap	Marks the image as an environment map.
`wrapmodes`	string	Texture extrapolation modes: black, clamp, periodic, mirror.
`multiView`	stringvector	View names for multi-view files, such as left and right eye.
`deepImageState`	deepImageState	Whether deep pixels are sorted and non-overlapping; not checked by the library.
`idManifest`	idManifest	ID manifest.

Deprecated attributes include dwaCompressionLevel, the quality setting for DWA, and renderingTransform and lookModTransform, which name CTL transforms. The byte layouts of deepImageState and idManifest are not given in the file layout document; the C++ library is the authority for them.

.EXR File Format – Attribute types

Predefined types

Channel list

Compression codes

Other codes

Standard optional attributes