OpenEXR is a high dynamic-range (HDR) image file format developed by Industrial Light & Magic for use in computer imaging applications. This package contains the following utility: exrdisplay: simple viewer for EXR images. Spectral Viewer crashes on special OpenEXR file format. This shall be addressed. Also, I would be for using the official OpenEXR library and failback to TinyEXR.
Revealing More Detail in OpenEXR Images
This section gives a short tutorial on using the exrdisplay program, which is included with the OpenEXR software distribution.
You can reveal more detail in OpenEXR images by changing the exposure using the Exposure slider. This operation is analogous to changing the exposure of a piece of film, lightening or darkening the image to reveal more detail at the high or low end.
With exrdisplay, however, changing the exposure does not affect image data itself, it simply changes the way that the original 16-bit floating-point pixel values in the image are converted to 8-bit integer data in the frame buffer. We call the original 16-bit FP pixels the 'raw' image data, and the converted 8-bit pixels the 'cooked' image data. When you change the exposure, you are 're-cooking' the data.
For example, in the following image you can see the light areas (fog) very clearly but in the dark areas (rock closest to camera) the detail is too dark to see. By changing the exposure to positive 3 (taking the image up 3 stops) the detail in the dark areas becomes visible. However, you lose the detail in the light areas because it is now too bright to see.
| Original image 0 exposure | Same image Exposure adjusted to positive 3 |
| (click for larger image) | (click for larger image) |
How Your Image Is Displayed
The Viewer has other sliders that you can use to specify how your 16-bit OpenEXR image is displayed on your 8-bit monitor:
- Exposure - sets the apparent exposure of the image on the display. It lightens or darkens the displayed image, allowing you to reveal detail in the high or low end.
- Defog - subtracted from pixel values to compensate for fogging due to stray light in the recording device.
- kneeHigh and kneeLow - pixel values between kneeHigh and kneeLow set the white level of the displayed image, determining which value is mapped to the maximum intensity of the monitor (exrdisplay lets you set the white level between 3.5 and 7 f-stops above middle gray).
The actual process for conversion from raw data to data ready for the display card happens like this (as taken from comments from the exrdisplay source code):
- Compensate for fogging by subtracting defog from the raw pixel values.
- Multiply the defogged pixel values by 2(exposure + 2.47393).
- Values, which are now 1.0, are called 'middle gray.' If defog and exposure are both set to 0.0, then middle gray corresponds to a raw pixel value of 0.18. In step 6, middle gray values will be mapped to an intensity 3.5 f-stops below the display's maximum intensity.
- Apply a knee function. The knee function has two parameters, kneeLow and kneeHigh. Pixel values below 2kneeLow are not changed by the knee function. Pixel values above kneeLow are lowered according to a logarithmic curve, such that the value 2kneeHigh is mapped to 23.5 (in step 6, this value will be mapped to the display's maximum intensity).
- Gamma-correct the pixel values, assuming that the screen's gamma is 2.2.
- Scale the values such that middle gray pixels are mapped to 84.66 (or 3.5 f-stops below the display's maximum intensity).
- Clamp the values to [0, 255].
| Filename extension | |
|---|---|
| Internet media type | image/x-exr |
| Developed by | Industrial Light & Magic |
| Initial release | 1999; 22 years ago |
| Latest release | 3.1.1 (2 August 2021; 10 days ago) |
| Type of format | High-dynamic-range imaging |
| Open format? | Yes, Modified BSD License |
| Website | www.openexr.com |
OpenEXR is a high-dynamic range, multi-channel rasterfile format, released as an open standard along with a set of software tools created by Industrial Light & Magic (ILM), under a free software license similar to the BSD license.[1]
It is notable for supporting multiple channels of potentially different pixel sizes, including 32-bit unsigned integer, 32-bit and 16-bit floating point values, as well as various compression techniques which include lossless and lossy compression algorithms. It also has arbitrary channels and encodes multiple points of view such as left- and right-camera images.[2]
Overview[edit]
A full technical introduction of the format is available on the OpenEXR website.[2]
OpenEXR, or EXR for short, is a deep raster format developed by ILM and broadly used in the computer-graphics industry, both visual effects and animation.
OpenEXR's multi-resolution and arbitrary channel format makes it appealing for compositing, as it alleviates several painful elements of the process. Since it can store arbitrary channels—specular, diffuse, alpha, RGB, normals, and various other types—in one file, it takes away the need to store this information in separate files. The multi-channel concept also reduces the necessity to 'bake' in the aforementioned data to the final image. If a compositer is not happy with the current level of specularity, they can adjust that specific channel.[3]
OpenEXR's API makes tools development a relative ease for developers. Since there are almost never two identical production pipelines, custom tools always need to be developed to address problems, e. g. image manipulation issue. OpenEXR's library allows quick and easy access to the image's attributes such as tiles and channels.[3]
History[edit]
OpenEXR was created by ILM in 1999 and released to the public in 2003 along with an open sourcesoftware library.[4][5] It soon received wide adoption by software used in computer graphics, particularly for film and television production. The format has been updated several times, adding support for tiles, mipmaps, new compression methods, and other features.[5] In 2007, OpenEXR was honored with an Academy Award for Technical Achievement.[5]
OpenEXR 2.0 was released in April 2013, extending the format with support for deep image buffers and multiple images embedded in a single file.[5][6][7] Version 2.2, released August 2014, added the lossy DWA compression format.[8]
Distribution[edit]
The OpenEXR software distribution includes:
- libraries
- Half, a C++ class for manipulating half values as if they were a built-in C++ data type
- exrdisplay, a sample application for viewing OpenEXR images on a display at various exposure settings
Libraries[edit]
- IlmImf[9] = library made by Industrial Light & Magic ( Ilm) for low-level operations on the files with OpenEXR image format (Imf)[10]
- libIlmImf on linux
- IlmImf.dll on windows
- IlmImfUtil
- Imath[11]
Color depth[edit]
OpenEXR has support for color depth using
- 16-bit floating-point ( half)
- 32-bit floating-point
- 32-bit integer
Compression methods[edit]
There are three general types of lossless compression built into OpenEXR, with two different methods of Zip compressing. For most images without a lot of grain, the two Zip compression methods seem to work best, while the PIZ compression algorithm is better suited to grainy images. The following options are available:[12]
- None
- Disables all compression.
- Run Length Encoding (RLE)
- This is a basic form of compression that is comparable to that used by standard Targa files.
- Zip (per scanline)
- deflate compression with zlib wrapper applied to individual scanlines (not based on the ZIP file format despite its name).
- Zip (16 scanline blocks)
- deflate compression applied to blocks of 16 scanlines at time. This tends to be the most effective style of compression to use with rendered images that do not have film grain applied.
- PIZ (wavelet compression)
- This lossless method uses a new combined wavelet / Huffman compression. This form of compression is quite effective when dealing with grainy images, and will often surpass any of the other options under grainy conditions.
- PXR24 (24-bit data conversion then deflate compression)
- This form of compression from Pixar Animation Studios converts 32-bit floats to 24 bits then uses deflate compression. It is lossless for half and 32-bit integer data and slightly lossy for 32-bit float data.
- B44
- This form of compression is lossy for half data and stores 32-bit data uncompressed. It maintains a fixed compression size of either 2.28:1 or 4.57:1 and is designed for realtime playback. B44 compresses uniformly regardless of image content. [13]
- B44A
- An extension to B44 where areas of flat color are further compressed, such as alpha channels.
- DWAA
- JPEG-like lossy compression format contributed by DreamWorks Animation. Compresses 32 scanlines together.[8]
- DWAB
- Same as DWAA, but compresses blocks of 256 scanlines.
Credits[edit]
From OpenEXR.org's Technical Introduction:
The ILM OpenEXR file format was designed and implemented by Florian Kainz, Wojciech Jarosz, and Rod Bogart. The PIZ compression scheme is based on an algorithm by Christian Rouet. Josh Pines helped extend the PIZ algorithm for 16-bit and found optimizations for the float-to-half conversions. Drew Hess packaged and adapted ILM's internal source code for public release and maintains the OpenEXR software distribution. The PXR24 compression method is based on an algorithm written by Loren Carpenter at Pixar Animation Studios.[2]
Developing with OpenEXR[edit]
The OpenEXR library is developed in C++ and is available in source format as well as compiled format for Microsoft Windows, macOS and Linux. Python bindings for the library are also available for version 2.x.[14]
As of version 1.3.0, released on 8 June 2006, support for multithreaded reading and writing was added to OpenEXR. Multithreaded reading and writing offers a higher performance gain for systems that have multiple cores or CPUs. OpenEXR handles reading and writing by a means of a thread pool.[citation needed]
See also[edit]
Openexr Viewer Linux
References[edit]
- ^License, openexr.com
- ^ abcFlorian Kainz; Rod Bogart; Piotr Stanczyk; Peter Hillman (5 November 2013). 'Technical Introduction to OpenEXR'(PDF). Industrial Light & Magic. Retrieved 2015-11-09.
- ^ abKainz, Florian. 'OpenEXR File Layout'(PDF). Industrial Light & Magic. Retrieved 7 December 2013.
- ^'Industrial Light & Magic Releases Proprietary Extended Dynamic Range Image File Format OpenEXR to Open Source Community'(PDF) (Press release). 22 January 2003. Archived from the original(PDF) on 21 July 2017. Retrieved 11 April 2013.
- ^ abcd'Main OpenEXR web site'.
- ^Stanczyk, Piotr (9 April 2013). 'v2.0.0.0 (GM) release announcement'. openexr-announce (Mailing list).
- ^'OpenEXR 2.0'. The CGSoceity. 10 April 2013.
- ^ ab'DreamWorks Animation Contributes Lossy Compression To OpenEXR 2.2' (Press release). Glendale, CA. 8 August 2014. Retrieved 2014-08-18.
- ^Reading and Writing OpenEXR Image Files with the IlmImf Library
- ^github AcademySoftwareFoundation openexr issue 879
- ^AcademySoftwareFoundation Imath library
- ^'Archived copy'(PDF). Archived from the original(PDF) on 2011-07-17. Retrieved 2006-02-23.CS1 maint: archived copy as title (link)
- ^'Archived copy'(PDF). Archived from the original(PDF) on 2011-07-17. Retrieved 2006-02-23.CS1 maint: archived copy as title (link)
- ^'OpenEXR 1.3.0 : Python Package Index'. pypi.python.org. Retrieved 11 April 2018.