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VFX File Exchange

In the high-quality areas of (cinema) film post production and in the area of ​​VFX single-frame sequences are still used as standard.

For high-quality workflows in feature film post-production and VFX, using rushes that are originated on a camera film, each negative needs to be run through a telecine or film scanner. In both cases the scanner generates DPX file sequences which are then used in the post production workflow. In addition, digital cinematography can produce RAW files which are then debayered into various file formats for post production. Whether this post production is for commercials, drama or the production of DCP /DCDM for film distribution, there are only a few common file formats used. These include DPX, TIFF and OpenEXR with different resolutions, colour sampling and bit depths and using one file per frame of image. None of these formats carry audio.

DPX

The Digital Picture Exchange (DPX) format was standardised and implemented in 2003 by SMPTE. It is a modification of the Cineon format from Kodak, which is used for storing uncompressed image data. With DPX there is a much larger file header for storing film or TV-specific metadata.

DPX is resolution independent. It can use different colour models such as RGB, XYZ or YCbCr and can store 8, 10, 12 or 16-bit data per channel either linearly, logarithmically or video gamma encoded. The DPX file can also carry an alpha channel. Multiple images (e.g. left and right eye stereoscopic frames or different high dynamic range exposures) can be contained as layers within a single DPX file.

DPX has been adopted for most high-end VFX and post-production work and is supported in all major post-production software. However, as it is an uncompressed file format it requires a large amount of data storage compared to compressed video files such as MPEG-4, AVC-I, DNxHD or ProRes DPX.

TIFF

The Tagged Image File Format (TIFF) was introduced in 1986 and the last update to version 6.0 took place in 1992.

It is possible to use TIFF files for any resolution, colour model, or compression method that is available – the limiting factor being only the software used with the TIFF file. For some TIFF file formats using a 32-bit offset restricts it to a maximum file size of 4GB. For other TIFF formats such as those used for motion pictures, there is not (yet) a theoretical limitation. It is customary to use TIFF files with RGB colour space and 8 or 16 bit or 32 bit floating point data per channel.

Within the print industry, where the TIFF format found widespread adoption due to its support for CMYK, the file size limitation can be more relevant.

TIFF is very widespread and ‘Baseline TIFF’ can be recognised by every TIFF reader software. The TIFF format was created by the Aldus Corporation which was subsequently acquired by Adobe and this file format has found widespread support especially within Adobe software.

OpenEXR

The OpenEXR file format was developed in 1999 by Industrial Light & Magic (ILM) and version 2.2 was introduced in 2014. It is an open and free standard through the OpenEXR organisation. OpenEXR files provide higher dynamic range and colour precision than previous VFX file formats.

It supports 16 bits or 32 bits floating-point and 32 bit integer pixel data per colour channel resulting in approximately 30 stops of dynamic range. 16 bit floating-point is sufficient to capture the whole range of information for most applications today and minimises storage space and file size.

OpenEXR can store multiple versions of the same image within the same file – for example different resolutions or separate colour grades. The image information in an OpenEXR file can be uncompressed, lossless or lossy.

From version 2.0 onwards, Z-depth information along with RGB colour data per pixel can also be stored.

DPX and TIFF files are both used in post production and VFX workflows and also used as delivery file formats. However, OpenEXR was designed specifically to be used for complex and highly integrated VFX and post production workflows but not as a final delivery format. It will normally be transcoded into another file format for final delivery of the completed project.

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