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README for OpenImageIO


The primary target audience for OIIO is VFX studios and developers of tools such as renderers, compositors, viewers, and other image-related software you'd find in a production pipeline.

OpenImageIO consists of:

  • Simple but powerful ImageInput and ImageOutput APIs that provide an abstraction for reading and writing image files of nearly any format, without the calling application needing to know any of the details of these file formats, and indeed without the calling application needing to be aware of which formats are available.
  • A library that manages subclasses of ImageInput and ImageOutput that implement I/O from specific file formats, with each file format's implementation stored as a plug-in. Therefore, an application using OpenImageIO's APIs can read and write any image file for which a plugin can be found at runtime.
  • Plugins implementing I/O for several popular image file formats, including TIFF, JPEG/JFIF, OpenEXR, PNG, HDR/RGBE, ICO, BMP, Targa, JPEG-2000, RMan Zfile, FITS, DDS, Softimage PIC, PNM, DPX, Cineon, IFF, Field3D, Ptex, Photoshop PSD, Wavefront RLA, SGI, and WebP. More are being developed all the time.
  • An image viewer, iv, that is based on ImageIO plugins and therefore can read images of any format for which an appropriate plugin may be found.
  • Several image tools based on these classes, including oiiotool (command-line format conversion and basic image processing), iinfo (print detailed info about images), iconvert (convert among formats, data types, or modify metadata), idiff (compare images), igrep (search images for matching metadata). Because these tools are based on ImageInput/ImageOutput, they work with any image formats for which ImageIO plugins are available.
  • An ImageCache class that transparently manages a cache so that it can access truly vast amounts of image data (tens of thousands of image files totaling multiple TB) very efficiently using only a tiny amount (tens of megabytes at most) of runtime memory.
  • A TextureSystem class that provides filtered MIP-map texture lookups, atop the nice caching behavior of ImageCache. This is used in commercial renderers and has been used on many large VFX and animated films.
  • ImageBuf and ImageBufAlgo functions -- a simple class for storing and manipulating whole images in memory, and a collection of the most useful computations you might want to do involving those images.


OpenImageIO is (c) Copyright 2008 by Larry Gritz and the other contributors. All Rights Reserved.

OpenImageIO is distributed using the modified BSD license. Please read the "LICENSE" file for the legal wording. The plain English bottom line is that OpenImageIO is free, as well as freely modifiable and redistributable (in both source and binary form). You may use part or all of it in your own applications, whether proprietary or open, free or commercial or not. Using it in a commercial or proprietary application DOES NOT obligate you to pay us, or to use any particular licensing terms in your own application.

Web Resources

Main web page:

GitHub page:

Mail lists:


Building and Installation

Please read the "INSTALL" file for detailed instructions on how to build and install OpenImageIO.

Remember that you need to set the environment variable IMAGEIO_LIBRARY_PATH to point to the 'lib' directory where OpenImageIO is installed, or else it will not be able to find the plugins.


The primary user and programmer documentation can be found in src/doc/openimageio.pdf (in a source distribution) or in the doc/openimageio.pdf file of an installed binary distribution.

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