Alternative University

Computer Science

Raster Image Storage

Higher Precision Extended Range

XRH File Format 3.0

The XRH file format (with  .xrh  file name extension) is a simple standard royalties-free file format for storing and archiving extended range raster image data.

XRH stores higher precision extended range still images.  The images could be any spatially correlated rectangular raster data, such as photographs, or geographic elevation data, etc. Each image contains one or more channels (also called image planes or components).

Extended range (XR) images are images that store more than 8 bits per channel. The number of bits per channel is called precision. Extended range images have higher precision.

XRH files can store images that are 32 bits or 64 bits per channel. Each value (sample) stored in a channel is a floating point number (Float32 or Float64).

Color sample values are stored as natural (linear) color values, because higher precision makes sample values more dense (eliminating the need to nonlinearly spread sample values).

In an XRH file, each channel of floating point numbers is stored compressed. Each channel can have its own Compression Type. The following Compression Types are currently supported:

Zebra is a lossless compression method using ZST to store Byte Channels of multi-byte samples: for example, four Byte Channels per 32-bit image channel, eight Byte Channels per 64-bit image channel, etc.

SZMOD is a lossy compression method for 32-bit and 64-bit floating point samples. It is a modular port of the SZ 2.1 compression method that uses 2nd-order Lorenzo prediction.

“we successfully leverage adaptive parameter optimization techniques with a series of optimization strategies on data prediction, which can significantly improve the compression quality for SZ with the same level of data distortion.”
— 
Kai Zhao, Sheng Di, et al., HPDC ’20, June 23–26, 2020, Stockholm, Sweden [DOI]

Source Code

Free proof-of-concept C source code for reading and writing XRH 3.0 files is provided with sample files.


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XRH 3.0 File Format
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Introduction (this page)
File Layout & Header
Comments
Custom Properties
Channel Names
Channels
Zebra Compression
SZMOD Compression
Color Transformations
Sample Files
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2022–Jan–24  11:31  UTC