OpenEXR
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# Standard Optional Attributes

By default, OpenEXR files have the following attributes:

chromaticities

  For RGB images, specifies the CIE (x,y) chromaticities of the primaries and the white point.

whiteLuminance

  For RGB images, defines the luminance, in Nits (candelas per square meter) of the RGB value (1.0, 1.0, 1.0).

  If the chromaticities and the whiteLuminance of an RGB image are known, then it is possible to convert the image’s pixels from RGB to CIE XYZ tristimulus values.

adoptedNeutral

  Specifies the CIE (x,y) coordinates that should be considered neutral during color rendering. Pixels in the image file whose (x,y) coordinates match the adoptedNeutral value should be mapped to neutral values on the display.

renderingTransform, lookModTransform

  Specify the names of the CTL functions that implements the intended color rendering and look modification transforms for this image.

xDensity

  Horizontal output density, in pixels per inch. The image’s vertical output density is xDensity * pixelAspectRatio.

owner

  Name of the owner of the image.

comments

  Additional image information in human-readable form, for example a verbal description of the image.

capDate

  The date when the image was created or captured, in local time, and formatted as `YYYY:MM:DD hh:mm:ss`, where `YYYY` is the year (4 digits, e.g. 2003), `MM` is the month (2 digits, 01, 02, … 12), `DD` is the day of the month (2 digits, 01, 02, … 31), hh is the hour (2 digits, 00, 01, … 23), mm is the minute, and ss is the second (2 digits, 00, 01, … 59).

utcOffset

  Universal Coordinated Time (UTC), in seconds: UTC == local time + utcOffset

longitude, latitude, altitude

  For images of real objects, the location where the image was recorded. Longitude and latitude are in degrees east of Greenwich and north of the equator. Altitude is in meters above sea level. For example, Kathmandu, Nepal is at longitude 85.317, latitude 27.717, altitude 1305.

focus

  The camera’s focus distance, in meters.

exposure

  Exposure time, in seconds.

aperture

  The camera’s lens aperture, in f-stops (focal length of the lens divided by the diameter of the iris opening).

isoSpeed

  The ISO speed of the film or image sensor that was used to record the image.

envmap

  If this attribute is present, the image represents an environment map. The attribute’s value defines how 3D directions are mapped to 2D pixel locations.

keyCode

  For motion picture film frames. Identifies film manufacturer, film type, film roll and frame position within the roll.

timeCode

  Time and control code

wrapmodes

  Determines how texture map images are extrapolated. If an OpenEXR file is used as a texture map for 3D rendering, texture coordinates (0.0, 0.0) and (1.0, 1.0) correspond to the upper left and lower right corners of the data window. If the image is mapped onto a surface with texture coordinates outside the zero-to-one range, then the image must be extrapolated. This attribute tells the renderer how to do this extrapolation. The attribute contains either a pair of comma-separated keywords, to specify separate extrapolation modes for the horizontal and vertical directions; or a single keyword, to specify extrapolation in both directions (e.g. “clamp,periodic” or “clamp”). Extra white space surrounding the keywords is allowed, but should be ignored by the renderer (“clamp, black “ is equivalent to “clamp,black”). The keywords listed below are predefined; some renderers may support additional extrapolation modes:

  black

    pixels outside the zero-to-one range are black

  clamp

    texture coordinates less than 0.0 and greater than 1.0 are clamped to 0.0 and 1.0 respectively.

  periodic

    the texture image repeats periodically

  mirror

    the texture image repeats periodically, but every other instance is mirrored

framesPerSecond

  Defines the nominal playback frame rate for image sequences, in frames per second. Every image in a sequence should have a framesPerSecond attribute, and the attribute value should be the same for all images in the sequence. If an image sequence has no framesPerSecond attribute, playback software should assume that the frame rate for the sequence is 24 frames per second.

  In order to allow exact representation of NTSC frame and field rates, framesPerSecond is stored as a rational number. A rational number is a pair of integers, n and d, that represents the value n/d.

multiView

  Defines the view names for multi-view image files. A multi-view image contains two or more views of the same scene, as seen from different viewpoints, for example a left-eye and a right-eye view for stereo displays. The multiView attribute lists the names of the views in an image, and a naming convention identifies the channels that belong to each view.

worldToCamera

  For images generated by 3D computer graphics rendering, a matrix that transforms 3D points from the world to the camera coordinate space of the renderer.

  The camera coordinate space is left-handed. Its origin indicates the location of the camera. The positive x and y axes correspond to the “right” and “up” directions in the rendered image. The positive z axis indicates the camera’s viewing direction. (Objects in front of the camera have positive z coordinates.)

  Camera coordinate space in OpenEXR is the same as in Pixar’s Renderman.

worldToNDC

  For images generated by 3D computer graphics rendering, a matrix that transforms 3D points from the world to the Normalized Device Coordinate (NDC) space of the renderer.

  NDC is a 2D coordinate space that corresponds to the image plane, with positive x and pointing to the right and y positive pointing down. The coordinates (0, 0) and (1, 1) correspond to the upper left and lower right corners of the OpenEXR display window.

  To transform a 3D point in word space into a 2D point in NDC space, multiply the 3D point by the worldToNDC matrix and discard the z coordinate.

  NDC space in OpenEXR is the same as in Pixar’s Renderman.

deepImageState

  Specifies whether the pixels in a deep image are sorted and non-overlapping.

  Note: this attribute can be set by application code that writes a file in order to tell applications that read the file whether the pixel data must be cleaned up prior to image processing operations such as flattening. The OpenEXR library does not verify that the attribute is consistent with the actual state of the pixels. Application software may assume that the attribute is valid, as long as the software will not crash or lock up if any pixels are inconsistent with the deepImageState attribute.

originalDataWindow

  If application software crops an image, then it should save the data window of the original, un-cropped image in the originalDataWindow attribute.

dwaCompressionLevel

  Sets the quality level for images compressed with the DWAA or DWAB method.

ID Manifest

  ID manifest.

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