- [Document Purpose and Audience](#document-purpose-and-audience)
- [Backwards Compatibility and New or Changed
Functionality](#backwards-compatibility-and-new-or-changed-functionality)
- [OpenEXR Backwards Compatibility (1.7 and
2.0)](#openexr-backwards-compatibility-17-and-20)
- [New Features for OpenEXR 2.0: Multi-Part and Deep
Data](#new-features-for-openexr-20-multi-part-and-deep-data)
- [Basic Data Types](#basic-data-types)
- [Integers](#integers)
- [Floating-Point Numbers](#floating-point-numbers)
- [Text](#text)
- [Packing](#packing)
- [File Layout](#file-layout)
- [`<span id="High-Level Layout">`{=html}`</span>`{=html}High-Level
Layout](#high-level-layout)
- [Comparison between Single-Part and Multi-Part File
Layouts](#comparison-between-single-part-and-multi-part-file-layouts)
- [Components One and Two: Magic Number and Version
Field](#components-one-and-two-magic-number-and-version-field)
- [Magic Number](#magic-number)
- [`<span id="anchor-1">`{=html}`</span>`{=html}Version
Field](#version-field)
- [Version field, valid values](#version-field-valid-values)
- [Component Three: Header](#component-three-header)
- [`<span id="anchor-2">`{=html}`</span>`{=html}Structure](#structure)
- [Single-part file](#single-part-file)
- [Multi-part file (new in 2.0)](#multi-part-file-new-in-20)
- [`<span id="Header Attribute">`{=html}`</span>`{=html}Attribute
Layout](#attribute-layout)
- [`<span id="Header Attributes - Required">`{=html}`</span>`{=html}Header
Attributes (All Files)](#header-attributes-all-files)
- [Tile Header Attribute](#tile-header-attribute)
- [Multi-View Header Attribute](#multi-view-header-attribute)
- [`<span id="anchor-3">`{=html}`</span>`{=html}Multi-Part and
Deep Data Header Attributes (New in
2.0)](#multi-part-and-deep-data-header-attributes-new-in-20)
- [Deep Data Header Attributes (New in
2.0)](#deep-data-header-attributes-new-in-20)
- [`<span id="anchor-4">`{=html}`</span>`{=html}Component Four: Offset
Tables](#component-four-offset-tables)
- [Offset Tables](#offset-tables)
- [Offset Table Size](#offset-table-size)
- [Scan Lines](#scan-lines)
- [Tiles](#tiles)
- [Multi-part (New in 2.0)](#multi-part-new-in-20)
- [Component Five: Pixel data](#component-five-pixel-data)
- [`<span id="anchor-5">`{=html}`</span>`{=html}Chunk Layout (New
in 2.0)](#chunk-layout-new-in-20)
- [Regular Scan Line Blocks](#regular-scan-line-blocks)
- [`<span id="anchor-7">`{=html}`</span>`{=html}Regular scan
line image block
layout](#regular-scan-line-image-block-layout)
- [Compressed data](#compressed-data)
- [Regular ImageTiles](#regular-imagetiles)
- [`<span id="anchor-8">`{=html}`</span>`{=html}Regular image
tile layout](#regular-image-tile-layout)
- [`<span id="anchor">`{=html}`</span>`{=html}Deep Data (New in
2.0)](#deep-data-new-in-20)
- [`<span id="anchor-9">`{=html}`</span>`{=html}Deep scan line
layout](#deep-scan-line-layout)
- [`<span id="anchor-10">`{=html}`</span>`{=html}Deep tiled
layout](#deep-tiled-layout)
- [Unpacked deep data chunks](#unpacked-deep-data-chunks)
- [Deep data compression](#deep-data-compression)
- [`<span id="anchor-6">`{=html}`</span>`{=html}Predefined Attribute
Types](#predefined-attribute-types)
- [Sample File](#sample-file)
OpenEXR File Layout
Last Update:
Florian Kainz
Industrial Light & Magic
# Document Purpose and Audience
This document gives an overview of the layout of OpenEXR 2.0 image files
as byte sequences. It covers both single and multi-part formats, and how
deep data is handled.
The text assumes that the reader is familiar with OpenEXR terms such as
\"channel\", \"attribute\", \"data window\" or \"chunk\". For an
explanation of those terms see the *Technical Introduction to OpenEXR*.
**Note:** This document does not define the OpenEXR file format. OpenEXR
is defined as the file format that is read and written by the IlmImf
open-source C++ library. If this document and the IlmImf library
disagree, then the library takes precedence.
# Backwards Compatibility and New or Changed Functionality
## OpenEXR Backwards Compatibility (1.7 and 2.0) {#openexr-backwards-compatibility-17-and-20}
OpenEXR 1.7 and earlier format files are fully supported by OpenEXR 2.0.
You can still use the 1.7 file format with the 2.0 library. If you use
the 2.0 format for single-part scan line image and tile image data, your
data will be stored in the same way as the 1.7 files. You can recompile
your 1.7 files to take advantage of the new format EXRs (multiple-part
files, and/or deep scan line and deep tile data).
## New Features for OpenEXR 2.0: Multi-Part and Deep Data {#new-features-for-openexr-20-multi-part-and-deep-data}
The multi-part format is an extension of the OpenEXR 1.7 single-part
file format. In addition to supporting the OpenEXR 1.7 data storage (a
single scan line or tiled image), OpenEXR 2.0 files can be used to store
multiple views and/or deep data (deep scan line or deep tiles).
While you can continue to use the 1.7 format for files, these changes to
the file layout are required to support the new multi-part and deep data
features:
```{=html}
<table>
<colgroup>
<col style="width: 33%" />
<col style="width: 33%" />
<col style="width: 33%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>Version field</td>
<td>Bits 11 and 12 indicate whether the file contains deep data (bit 11), or more than one part (bit 12).</td>
<td><em><a href="#anchor">Deep Data</a></em> on page <a href="#anchor-1">6</a></td>
</tr>
<tr class="even even">
<td>Header</td>
<td>To store more than one part in the file, you need to have a header for each part.</td>
<td><em><a href="#anchor-2">Structure</a></em> on page <a href="#anchor-2">7</a></td>
</tr>
<tr class="odd odd">
<td>Header attributes</td>
<td>There are a number of attributes which have been defined to store data which is relevant to deep data and multi-part files. These include: name (one for each part), data type (you can have different types of data in different views), and the maximum number of samples to take in a deep data channel.</td>
<td><em><a href="#anchor-3">Multi-Part and Deep Data Header Attributes</a></em> on page <a href="#anchor-3">9</a></td>
</tr>
<tr class="even even">
<td>Offset tables and chunks</td>
<td><p>To store more than one part in the file, you need to have an offset table for each part, and chunks for each part.</p>
<p>The chunks must begin with a part number.</p></td>
<td><em><a href="#anchor-4">Component Four: Offset Tables</a></em> on page <a href="#anchor-4">10</a>, and <em><a href="#anchor-5">Chunk Layout</a></em> on page <a href="#anchor-5">11</a>.</td>
</tr>
<tr class="odd odd">
<td>Deep Data</td>
<td>Deep data has a unique storage format.</td>
<td><em><a href="#anchor">Deep Data</a></em> on page <a href="#anchor">13</a></td>
</tr>
</tbody>
</table>
```
# Basic Data Types
An OpenEXR file is a sequence of 8-bit bytes. Groups of bytes represent
basic objects such as integral numbers, floating-point numbers and text.
Those objects are grouped together to form compound objects such as
attributes or scan lines.
## Integers
Binary integral numbers with 8, 16, 32 or 64 bits are stored as 1, 2, 4
or 8 bytes. Integral numbers can be signed or unsigned. Signed numbers
are represented using two\'s complement. Integral numbers are
little-endian (that is, the least significant byte is closest to the
start of the file).
OpenEXR uses the following six integer data types:
------------------ ----- ---
*unsigned char* no 1
*short* yes 2
*unsigned short* no 2
*int* yes 4
*unsigned int* no 4
*unsigned long* no 8
------------------ ----- ---
## Floating-Point Numbers
Binary floating-point numbers with 16, 32 or 64 bits are stored as 2, 4
or 8 bytes. The representation of 32-bit and 64-bit floating-point
numbers conforms to the IEEE 754 standard. The representation of 16-bit
floating-point numbers is analogous to IEEE 754, but with 5 exponent
bits and 10 bits for the fraction. The exponent bias is 15.
Floating-point numbers are little-endian (that is: the least significant
bits of the fraction are in the byte closest to the beginning of the
file, while the sign bit and the most significant bits of the exponent
are in the byte closest to the end of the file).
The following table lists the names and sizes of OpenEXR\'s
floating-point data types:
---------- ---
*half* 2
*float* 4
*double* 8
---------- ---
## Text
Text strings are represented as sequences of 1-byte characters of type
*char*. Depending on the context, either the end of a string is
indicated by a null character (0x00), or the length of the string is
indicated by an *int* that precedes the string.
## Packing
Data in an OpenEXR file are densely packed; the file contains no
\"padding\". For example, consider the following C struct:
struct SI
{
short s;
int i;
};
On most computers, the in-memory representation of an *SI* object
occupies 8 bytes: 2 bytes for *s*, 2 padding bytes to ensure four-byte
alignment of *i*, and 4 bytes for *i*. In an OpenEXR file the same
object would consume only 6 bytes: 2 bytes for *s* and 4 bytes for *i*.
The 2 padding bytes are not stored in the file.
# File Layout
## `<span id="High-Level Layout">`{=html}`</span>`{=html}High-Level Layout
Depending on whether the pixels in an OpenEXR file are stored as scan
lines or as tiles, the file consists of the following components:
```{=html}
<table>
<colgroup>
<col style="width: 25%" />
<col style="width: 25%" />
<col style="width: 25%" />
<col style="width: 25%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>scan lines:</td>
<td>tiles:</td>
<td></td>
<td></td>
</tr>
<tr class="even even">
<td>one</td>
<td>magic number</td>
<td>magic number</td>
<td>magic number</td>
</tr>
<tr class="odd odd">
<td>two</td>
<td>version field</td>
<td>version field</td>
<td>version field</td>
</tr>
<tr class="even even">
<td>three</td>
<td>header</td>
<td>header</td>
<td><p>part 0 header</p>
<p>[part 1 header]</p>
<p>...</p>
<p>[<empty header>]</p></td>
</tr>
<tr class="odd odd">
<td>four</td>
<td>line offset table</td>
<td>tile offset table</td>
<td><p>part 0 chunk offset table</p>
<p>[part 1 chunk offset table]</p>
<p>...</p></td>
</tr>
<tr class="even even">
<td>five</td>
<td>scan line blocks</td>
<td>tiles</td>
<td><em>chunks</em></td>
</tr>
</tbody>
</table>
```
It is the version field part which indicates whether the file is single
or multi-part and whether the file contains deep data. "Chunk" is a
general term to describe blocks of pixel data. A chunk can be a scan
line block, a tile or deep data (scan line or tile).
Deep data has no unique component structure of its own, but uses the
structure that the file would have if it did not have deep data in it.
## Comparison between Single-Part and Multi-Part File Layouts
Multi-part files have the same high level structure as single-part
OpenEXR files, except the header, offset table and chunk components can
have any number (two or more) parts. There must be the same number of
headers as offset tables, and they must be in the same order. In
addition, the header component of a multi-part file must end with a null
byte (0x00). In multi-part files, each chunk contains a field that
indicates which part\'s data it contains.
# Components One and Two: Magic Number and Version Field
## Magic Number
The magic number, of type *int*, is always 20000630 (decimal). It allows
file readers to distinguish OpenEXR files from other files, since the
first four bytes of an OpenEXR file are always 0x76, 0x2f, 0x31 and
0x01.
## `<span id="anchor-1">`{=html}`</span>`{=html}Version Field
The version field, of type *int*, is the four-byte group following the
magic number, and it is treated as two separate bit fields.
```{=html}
<table>
<colgroup>
<col style="width: 50%" />
<col style="width: 50%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>Byte/bit position</td>
<td>Description and notes</td>
</tr>
<tr class="even even">
<td>first byte<br />
(bits 0 through 7)</td>
<td><p>The 8 least significant bits, they contain the file format version number.</p>
<p>The current OpenEXR version number is version 2.</p></td>
</tr>
<tr class="odd odd">
<td>second, third and fourth bytes<br />
(bits 8 through 31)</td>
<td><p>The 24 most significant bits, these are treated as a set of boolean flags.</p>
<p>The remaining 19 flags in the version field are currently unused and should be set to 0.</p></td>
</tr>
</tbody>
</table>
```
### Version field, valid values
All valid combinations of the version field bits are as follows:
```{=html}
<table>
<colgroup>
<col style="width: 20%" />
<col style="width: 20%" />
<col style="width: 20%" />
<col style="width: 20%" />
<col style="width: 20%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>Description</td>
<td>Compatible with</td>
<td>bit 9</td>
<td>bit 11</td>
<td>bit 12</td>
</tr>
<tr class="even even">
<td>Single-part scan line.<br />
One normal scan line image.</td>
<td>All versions of OpenEXR.</td>
<td>0</td>
<td>0</td>
<td>0</td>
</tr>
<tr class="odd odd">
<td>Single-part tile.<br />
One normal tiled image.</td>
<td>All versions of OpenEXR.</td>
<td>1</td>
<td>0</td>
<td>0</td>
</tr>
<tr class="even even">
<td>Multi-part (new in 2.0).<br />
Multiple normal images (scan line and/or tiled).</td>
<td>OpenEXR 2.0.</td>
<td>0</td>
<td>0</td>
<td>1</td>
</tr>
<tr class="odd odd">
<td>Single-part deep data (new in 2.0).<br />
One deep tile or deep scan line part.</td>
<td>OpenEXR 2.0.</td>
<td>0</td>
<td>1</td>
<td>0</td>
</tr>
<tr class="even even">
<td>Multi-part deep data (new in 2.0).<br />
Multiple parts (any combination of: tiles, scan lines, deep tiles and/or deep scan lines).</td>
<td>OpenEXR 2.0.</td>
<td>0</td>
<td>1</td>
<td>1</td>
</tr>
</tbody>
</table>
```
**Note:** The version field bits define what capabilities must be
available in the software so it can handle the file, rather than the
exact format of the file. While the 9 and 11 bit settings must agree
with the type attributes of all parts, in OpenEXR 2.0 the data format of
each type is definitively set by the type attribute in that part\'s
header alone.
# Component Three: Header
## `<span id="anchor-2">`{=html}`</span>`{=html}Structure
### Single-part file
The header component of the single-part file holds a single header (for
single-part files).
Each header is a sequence of attributes ended by a null byte.
The file has the same structure as a 1.7 file. That is, the multi-part
bit (bit 12) must be 0, and the single null byte that signals the end of
the headers must be omitted. This structure also applies to single-part
deep data files.
### Multi-part file (new in 2.0) {#multi-part-file-new-in-20}
The header component of a multi-part file holds a set of headers, with a
separate header for each part (in multi-part files) and a null byte
signalling the end of the header component:
```{=html}
<table>
<colgroup>
<col style="width: 100%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td><p>part 0 header</p>
<p>[part 1 header]</p>
<p>...</p>
<p>[<empty header>]</p></td>
</tr>
</tbody>
</table>
```
Each header is a sequence of attributes ended by a null byte.
The multipart bit (bit 12) must be set to 1, and the list of headers
must be followed by a single null byte (0x00) (that is, an empty
header).
## `<span id="Header Attribute">`{=html}`</span>`{=html}Attribute Layout
The layout of an attribute is as follows:
-----------------
attribute type
attribute size
attribute value
-----------------
The **attribute name** and the **attribute type** are null-terminated
text strings. Excluding the null byte, the name and type must each be as
least 1 byte and at most :
- 31 bytes long (if bit 10 is set to 0), or
- 255 bytes long (if bit 10 is set to 1).
Both single-part and multi-part files use the same attribute types.
The **attribute size**, of type *int*, indicates the size (in bytes) of
the attribute value.
The layout of the **attribute value** depends on the attribute type. The
IlmImf library predefines several different attribute types (see page
[14](#anchor-6)). Application programs can define and store additional
attribute types.
## `<span id="Header Attributes - Required">`{=html}`</span>`{=html}Header Attributes (All Files)
The header of every OpenEXR file must contain at least the following
attributes:
---------------------- ---------------
*channels* *chlist*
*compression* *compression*
*dataWindow* *box2i*
*displayWindow* *box2i*
*lineOrder* *lineOrder*
*pixelAspectRatio* *float*
*screenWindowCenter* *v2f*
*screenWindowWidth* *float*
---------------------- ---------------
For descriptions of what these attributes are for, see the *Technical
Introduction to OpenEXR*.
## Tile Header Attribute
This attributes is required in the header for all files which contain
one or more tiles:
```{=html}
<table>
<colgroup>
<col style="width: 33%" />
<col style="width: 33%" />
<col style="width: 33%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>tiles</td>
<td>tiledesc</td>
<td><p>Determines the size of the tiles and the number of resolution levels in the file.</p>
<p><strong>Note:</strong> The IlmImf library ignores tile description attributes in scan line based files. The decision whether the file contains scan lines or tiles is based on the value of bit 9 in the file's version field, not on the presence of a tile description attribute.</p></td>
</tr>
</tbody>
</table>
```
## Multi-View Header Attribute
This attribute can be used in the header for multi-part files:
-------- -------- --
*view* *text*
-------- -------- --
## `<span id="anchor-3">`{=html}`</span>`{=html}Multi-Part and Deep Data Header Attributes (New in 2.0) {#multi-part-and-deep-data-header-attributes-new-in-20}
These attributes are required in the header for all multi-part and/or
deep data OpenEXR files.
```{=html}
<table>
<colgroup>
<col style="width: 33%" />
<col style="width: 33%" />
<col style="width: 33%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td><em>name</em></td>
<td><em>string</em></td>
<td>Required if either the multipart bit (12) or the non-image bit (11) is set.</td>
</tr>
<tr class="even even">
<td>type</td>
<td>string</td>
<td><p>Required if either the multipart bit (12) or the non-image bit (11) is set.</p>
<p>Set to one of:</p>
<p><strong>Note:</strong> This value must agree with the version field's tile bit (9) and non-image (deep data) bit (11) settings.</p></td>
</tr>
<tr class="odd odd">
<td>version</td>
<td>int</td>
<td><p>This document describes version 1 data for all part types.</p>
<p>version is required for deep data (deepscanline and deeptile) parts. If not specified for other parts, assume version=1.</p></td>
</tr>
<tr class="even even">
<td><em>chunkCount</em></td>
<td><em>int</em></td>
<td>Required if either the multipart bit (12) or the non-image bit (11) is set.</td>
</tr>
<tr class="odd odd">
<td><em>tiles</em></td>
<td><em>tileDesc</em></td>
<td>Required for parts of type <em>tiledimage</em> and <em>deeptile</em>.</td>
</tr>
</tbody>
</table>
```
For more information about the standard OpenEXR attributes and optional
attributes such as *preview images*, see the *OpenEXR File Layout*
document.
## Deep Data Header Attributes (New in 2.0) {#deep-data-header-attributes-new-in-20}
These attributes are required in the header for all files which contain
deep data (deepscanline or deeptile):
```{=html}
<table>
<colgroup>
<col style="width: 33%" />
<col style="width: 33%" />
<col style="width: 33%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td><em>tiles</em></td>
<td><em>tileDesc</em></td>
<td>Required for parts of type tiledimage and deeptile.</td>
</tr>
<tr class="even even">
<td><em>maxSamplesPerPixel</em></td>
<td><em>int</em></td>
<td><p>Required for deep data (deepscanline and deeptile) parts.</p>
<p><strong>Note:</strong> Since the value of <strong>maxSamplesPerPixel</strong> maybe be unknown at the time of opening the file, the value “<em>-1</em>” is written to the file to indicate an unknown value. When the file is closed, this will be overwritten with the correct value. If file writing does not complete correctly due to an error, the value <em>-1</em> will remain. In this case, the value must be derived by decoding each chunk in the part.</p></td>
</tr>
<tr class="odd odd">
<td>version</td>
<td>int</td>
<td>Should be set to <em>1</em>. It will be changed if the format is updated.</td>
</tr>
<tr class="even even">
<td>type</td>
<td>string</td>
<td>Must be set to <em>deepscanline</em> or <em>deeptile</em>.</td>
</tr>
</tbody>
</table>
```
For information about channel layout and a list of reserved channel
names, see the *Technical Introduction to OpenEXR* document, C*hannel
Names* section.
# `<span id="anchor-4">`{=html}`</span>`{=html}Component Four: Offset Tables
## Offset Tables
An offset table allows random access to pixel data chunks. An offset
table is a sequence of offsets, with one offset per chunk. Each offset
(of type *unsigned long*) indicates the distance, in bytes, between the
start of the file and the start of the chunk.
Chunks can be of any of the four data types.
## Offset Table Size
The number of entries in an offset table is defined in one of two ways:
1. If the multipart (12) bit is unset and the chunkCount is not
present, the number of entries in the chunk table is computed using
the dataWindow and tileDesc attributes and the compression format.
2. If the multipart (12) bit is set, the header must contain a
chunkCount attribute (which indicates the size of the table and the
number of chunks).
## Scan Lines
For scan line blocks, the line offset table is a sequence of scan line
offsets, with one offset per scan line block. In the table, scan line
offsets are ordered according to increasing scan line y coordinates.
## Tiles
For tiles, the offset table is a sequence of tile offsets, one offset
per tile. In the table, scan line offsets are sorted the same way as
tiles in *INCREASING_Y* order.
## Multi-part (New in 2.0) {#multi-part-new-in-20}
For multi-part files, each part defined in the header component has a
corresponding chunk offset table.
# Component Five: Pixel data
## `<span id="anchor-5">`{=html}`</span>`{=html}Chunk Layout (New in 2.0) {#chunk-layout-new-in-20}
A "chunk" is a general term for a pixel data block. The scan line and
tile images have the same format that they did in OpenEXR 1.7. OpenEXR
2.0 introduces two new types (deep scan line and deep tile).
The layout of each chunk is as follows:
--------------------------------------------
\[part number\] (if multi-part bit is set)
chunk data
--------------------------------------------
The **part number** (of type *unsigned long*) is only present in
multi-part files. It indicates which part this chunk belongs to. 0
indicates the chunk belongs to the part defined by the first header and
the first chunk offset table. The part number is omitted if the
multi-part bit (12) is not set (this saves space and enforces backwards
compatibility to software which does not support multi-part files).
The **chunk data** is dependent on the type attribute - but (other than
the part number) has the same structure as a single-part file of the
same format:
```{=html}
<table>
<colgroup>
<col style="width: 33%" />
<col style="width: 33%" />
<col style="width: 33%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>scan line</td>
<td>indicated by a type attribute of “scanlineimage”</td>
<td><p>Each chunk stores a scan line block, with the minimum y coordinate of the scan line(s) within the chunk.</p>
<p>See <em><a href="#anchor-7">Regular scan line image block layout</a>,</em> on page <a href="#anchor-7">12</a>.</p></td>
</tr>
<tr class="even even">
<td>tiled</td>
<td>indicated by a type attribute of “tiledimage”</td>
<td>See <em><a href="#anchor-8">Regular image tile layout</a>,</em> on page <a href="#anchor-8">12</a>.</td>
</tr>
<tr class="odd odd">
<td>deep scan line</td>
<td>indicated by a type attribute of “deepscanline”</td>
<td>See <em><a href="#anchor-9">Deep scan line layout</a>,</em> on page <a href="#anchor-9">13</a>.</td>
</tr>
<tr class="even even">
<td>deep tile</td>
<td>indicated by a type attribute of “deeptile”</td>
<td>See <em><a href="#anchor-10">Deep tiled layout</a>,</em> on page <a href="#anchor-10">13</a>.</td>
</tr>
</tbody>
</table>
```
For more information about data types, see page [Error: Reference source
not found](#anchor-11).
## Regular Scan Line Blocks
For scan line images and deep scan line images, one or more scan lines
may be stored together as a scan line block. The number of scan lines
per block depends on how the pixel data are compressed:
--------------------- ---- --
*NO_COMPRESSION* 1
*RLE_COMPRESSION* 1
*ZIPS_COMPRESSION* 1
*ZIP_COMPRESSION* 16
*PIZ_COMPRESSION* 32
*PXR24_COMPRESSION* 16
*B44_COMPRESSION* 32
*B44A_COMPRESSION* 32
--------------------- ---- --
Each scan line block has a y coordinate of type *int*. The block\'s y
coordinate is equal to the pixel space y coordinate of the top scan line
in the block. The top scan line block in the image is aligned with the
top edge of the data window (that is, the y coordinate of the top scan
line block is equal to the data window\'s minimum y).
If the height of the image\'s data window is not a multiple of the
number of scan lines per block, then the block that contains the bottom
scan line contains fewer scan lines than the other blocks.
### `<span id="anchor-7">`{=html}`</span>`{=html}Regular scan line image block layout
The layout of a regular image scan line block is as follows:
-----------------
y coordinate
pixel data size
pixel data
-----------------
The **pixel data size**, of type *int*, indicates the number of bytes
occupied by the actual pixel data.
Within the **pixel data**, scan lines are stored top to bottom. Each
scan line is contiguous, and within a scan line the data for each
channel are contiguous. Channels are stored in alphabetical order,
according to channel names. Within a channel, pixels are stored left to
right.
### Compressed data
If the file\'s compression method is *NO_COMPRESSION*, then the
original, uncompressed pixel data are stored directly in the file.
Otherwise, the uncompressed pixels are fed to the appropriate
compressor, and either the compressed or the uncompressed data are
stored in the file, whichever is smaller.
The layout of the compressed data depends on which compression method
was applied. The compressed formats are not described here. For
information on the compressed data formats, see the source code for the
IlmImf library.
## Regular ImageTiles
### `<span id="anchor-8">`{=html}`</span>`{=html}Regular image tile layout
The layout of a regular image tile is as follows:
------------------
tile coordinates
pixel data size
pixel data
------------------
The **tile coordinates**, a sequence of four *int*s (tileX, tileY,
levelX, levelY) indicates the tile\'s position and resolution level. The
**pixel data size**, of type *int*, indicates the number of bytes
occupied by the pixel data.
The **pixel data** in a tile are laid out in the same way as in a scan
line block, but the length of the scan lines is equal to the width of
the tile, and the number of scan lines is equal to the height of the
tile.
If the width of a resolution level is not a multiple of the file\'s tile
width, then the tiles at the right edge of that resolution level have
shorter scan lines. Similarly, if the height of a resolution level is
not a multiple of the file\'s tile height, then tiles at the bottom edge
of the resolution level have fewer scan lines.
## `<span id="anchor">`{=html}`</span>`{=html}Deep Data (New in 2.0) {#deep-data-new-in-20}
Deep images store an arbitrarily long list of data at each pixel
location (each pixel contains a list of samples, and each sample
contains a fixed number of channels).
### `<span id="anchor-9">`{=html}`</span>`{=html}Deep scan line layout
Deep scan line images are indicated by a type attribute of
"deepscanline". Each chunk of deep scan line data is a single scan line
of data. The data in each chunk is laid out as follows:
-------------------------------------------
\[part number\] (if multipart bit is set)
y coordinate
packed size of pixel offset table
packed size of sample data
unpacked size of sample data
compressed pixel offset table
compressed sample data
-------------------------------------------
The **unpacked size of the sample data** (an *unsigned long*) is the
size of the deep sample data once it is unpacked. It is necessary to
specify the unpacked size since the data may be arbitrarily large (so
generally cannot otherwise be determined without decompressing the data
first).
### `<span id="anchor-10">`{=html}`</span>`{=html}Deep tiled layout
Tiled images are indicated by a type attribute of "deeptile". Each chunk
of deep tile data is a single tile. The data in each chunk is laid out
as follows:
-------------------------------------------
\[part number\] (if multipart bit is set)
tile coordinates
packed size of pixel offset table
packed size of sample data
unpacked size of sample data
compressed pixel offset table
compressed sample data
-------------------------------------------
The **unpacked size of the sample data** (an *unsigned long*) is the
size of the deep data once it is unpacked. It is necessary to specify
the unpacked size since the data may be arbitrarily large (so generally
cannot otherwise be determined without decompressing the data first).
The **pixel offset table** is a list of *int*s, one for each column
within the dataWindow. Each entry *n* in the table indicates the total
number of samples required to store the pixel in *n* as well as all
pixels to the left of it. Thus, the first samples stored in each channel
of the pixel data are for the pixel in column 0, which contains
table\[1\] samples. Each channel contains table\[width-1\] samples in
total.
### Unpacked deep data chunks
When decompressed, the unpacked chunk consists of the channel data
stored in a non-interleaved fashion:
```{=html}
<table>
<colgroup>
<col style="width: 100%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td><p>pixel sample data for channel 0</p>
<p>pixel sample data for channel 1</p>
<p>pixel sample data for channel ...</p>
<p>pixel sample data for channel n</p></td>
</tr>
</tbody>
</table>
```
**Exception:** For ZIP_COMPRESSION only there will be up to 16 scanlines
in the packed sample data block:
```{=html}
<table>
<colgroup>
<col style="width: 100%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td><p>pixel sample data for channel 0 for scanline 0</p>
<p>pixel sample data for channel 1 for scanline 0</p>
<p>pixel sample data for channel ... for scanline 0</p>
<p>pixel sample data for channel n for scanline 0</p>
<p>pixel sample data for channel 0 for scanline 1</p>
<p>pixel sample data for channel 1 for scanline 1</p>
<p>pixel sample data for channel ... for scanline 1</p>
<p>pixel sample data for channel n for scanline 1</p>
<p>...</p></td>
</tr>
</tbody>
</table>
```
### Deep data compression
The following compression schemes are the only ones permitted for deep
data:
-------------------- ---- --
*NO_COMPRESSION* 1
*RLE_COMPRESSION* 1
*ZIPS_COMPRESSION* 1
*ZIP_COMPRESSION* 16
-------------------- ---- --
# `<span id="anchor-6">`{=html}`</span>`{=html}Predefined Attribute Types
The IlmImf library predefines the following attribute types:
```{=html}
<table>
<colgroup>
<col style="width: 50%" />
<col style="width: 50%" />
</colgroup>
<tbody>
<tr class="odd odd">
<td>box2i</td>
<td>Four <em>int</em>s: xMin, yMin, xMax, yMax</td>
</tr>
<tr class="even even">
<td>box2f</td>
<td>Four <em>float</em>s: xMin, yMin, xMax, yMax</td>
</tr>
<tr class="odd odd">
<td>chlist</td>
<td><p>A sequence of channels followed by a null byte (0x00).</p>
<p>Channel layout:</p></td>
</tr>
<tr class="even even">
<td>chromaticities</td>
<td>Eight <em>float</em>s: redX, redY, greenX, greenY, blueX, blueY, whiteX, whiteY</td>
</tr>
<tr class="odd odd">
<td>compression</td>
<td><p><em>unsigned</em> <em>char</em>, possible values are</p>
<p><em>NO_COMPRESSION</em> = 0</p>
<p><em>RLE_COMPRESSION</em> = 1</p>
<p><em>ZIPS_COMPRESSION</em> = 2</p>
<p><em>ZIP_COMPRESSION</em> = 3</p>
<p><em>PIZ_COMPRESSION</em> = 4</p>
<p><em>PXR24_COMPRESSION</em> = 5</p>
<p><em>B44_COMPRESSION</em> = 6</p>
<p><em>B44A_COMPRESSION</em> = 7</p></td>
</tr>
<tr class="even even">
<td>double</td>
<td><em>double</em></td>
</tr>
<tr class="odd odd">
<td>envmap</td>
<td><p><em>unsigned</em> <em>char</em>, possible values are:</p>
<p><em>ENVMAP_LATLONG</em> = 0</p>
<p><em>ENVMAP_CUBE</em> = 1</p></td>
</tr>
<tr class="even even">
<td>float</td>
<td><em>float</em></td>
</tr>
<tr class="odd odd">
<td>int</td>
<td><em>int</em></td>
</tr>
<tr class="even even">
<td>keycode</td>
<td>Seven <em>int</em>s: filmMfcCode, filmType, prefix, count, perfOffset, perfsPerFrame, perfsPerCount</td>
</tr>
<tr class="odd odd">
<td>lineOrder</td>
<td><p><em>unsigned</em> <em>char</em>, possible values are:</p>
<p><em>INCREASING_Y</em> = 0</p>
<p><em>DECREASING_Y</em> = 1</p>
<p><em>RANDOM_Y</em> = 2</p></td>
</tr>
<tr class="even even">
<td>m33f</td>
<td>9 <em>float</em>s</td>
</tr>
<tr class="odd odd">
<td>m44f</td>
<td>16 <em>float</em>s</td>
</tr>
<tr class="even even">
<td>preview</td>
<td><p>Two <em>unsigned int</em>s, width and height, followed by 4×width×height <em>unsigned char</em>s of pixel data.</p>
<p>Scan lines are stored top to bottom; within a scan line pixels are stored from left to right. A pixel consists of four <em>unsigned char</em>s, R, G, B, A.</p></td>
</tr>
<tr class="odd odd">
<td>rational</td>
<td>An <em>int</em>, followed by an <em>unsigned int</em>.</td>
</tr>
<tr class="even even">
<td>string</td>
<td>String length, of type <em>int</em>, followed by a sequence of <em>char</em>s.</td>
</tr>
<tr class="odd odd">
<td>stringvector</td>
<td>A sequence of zero or more text strings. Each string is represented as a string length, of type <em>int</em>, followed by a sequence of <em>chars</em>. The number of strings can be inferred from the total attribute size (see the <em><a href="#Header%20Attribute">Attribute Layout</a></em> section, on page <a href="#Header%20Attribute">8</a>).</td>
</tr>
<tr class="even even">
<td>tiledesc</td>
<td><p>Two <em>unsigned</em> <em>int</em>s: xSize, ySize, followed by mode, of type <em>unsigned char</em>, where</p>
<p><em></em> mode = levelMode + roundingMode×16</p>
<p>Possible values for levelMode:</p>
<p><em>ONE_LEVEL</em> = 0</p>
<p><em>MIPMAP_LEVELS</em> = 1</p>
<p><em>RIPMAP_LEVELS</em> = 2</p>
<p>Possible values for roundingMode:</p>
<p><em>ROUND_DOWN</em> = 0</p>
<p><em>ROUND_UP</em> = 1</p></td>
</tr>
<tr class="odd odd">
<td>timecode</td>
<td>Two <em>unsigned int</em>s: timeAndFlags, userData.</td>
</tr>
<tr class="even even">
<td>v2i</td>
<td>Two <em>int</em>s</td>
</tr>
<tr class="odd odd">
<td>v2f</td>
<td>Two <em>float</em>s</td>
</tr>
<tr class="even even">
<td>v3i</td>
<td>Three <em>int</em>s.</td>
</tr>
<tr class="odd odd">
<td>v3f</td>
<td>Three <em>float</em>s.</td>
</tr>
</tbody>
</table>
```
# Sample File
The following is an annotated byte-by-byte listing of a complete OpenEXR
file. The file contains a scan-line based image with four by three
pixels. The image has two channels: G, of type *HALF*, and Z, of type
*FLOAT*. The pixel data are not compressed. The entire file is 415 bytes
long.
The first line of text in each of the gray boxes below lists up to 16
bytes of the file in hexadecimal notation. The second line in each box
shows how the bytes are grouped into integers, floating-point numbers
and text strings. The third and fourth lines indicate how those basic
objects form compound objects such as attributes or the line offset
table.
--------------------------------------------------
20000630 \| 2 \| c h a n n e l s
magic number \| version, flags \| attribute name
\| \| start of header
--------------------------------------------------
--------------------------------------------------------
00 63 68 6c 69 73 74 00 25 00 00 00 47 00 01 00
\\0 \| c h l i s t \\0 \| 37 \| G \\0 \| HALF
\| attribute type \| attribute size \| attribute value
--------------------------------------------------------
-------------------------------------------------
00 00 00 00 00 00 01 00 00 00 01 00 00 00 5a 00
\| 0 \| 0 \| 1 \| 1 \| Z \\0 \|
-------------------------------------------------
-------------------------------------------------
02 00 00 00 00 00 00 00 01 00 00 00 01 00 00 00
FLOAT \| 0 \| 0 \| 1 \| 1 \|
\|
-------------------------------------------------
-------------------------------------------------
00 63 6f 6d 70 72 65 73 73 69 6f 6e 00 63 6f 6d
\\0 \| c o m p r e s s i o n \\0 \| c o m
\| attribute name \| attribute type
-------------------------------------------------
-------------------------------------------------
70 72 65 73 73 69 6f 6e 00 01 00 00 00 00 64 61
p r e s s i o n \\0 \| 1 \| NONE\| d a
\| attribute size \|value\|
-------------------------------------------------
-------------------------------------------------
74 61 57 69 6e 64 6f 77 00 62 6f 78 32 69 00 10
t a W i n d o w \\0 \| b o x 2 i \\0 \|
attribute name \| attribute type \|
-------------------------------------------------
-------------------------------------------------
00 00 00 00 00 00 00 00 00 00 00 03 00 00 00 02
16 \| 0 \| 0 \| 3 \|
attribute size\| attribute value
-------------------------------------------------
-------------------------------------------------
00 00 00 64 69 73 70 6c 61 79 57 69 6e 64 6f 77
2 \| d i s p l a y W i n d o w
\| attribute name
-------------------------------------------------
--------------------------------------------------------
00 62 6f 78 32 69 00 10 00 00 00 00 00 00 00 00
\\0 \| b o x 2 i \\0 \| 16 \| 0 \|
\| attribute type \| attribute size \| attribute value
--------------------------------------------------------
-------------------------------------------------
00 00 00 03 00 00 00 02 00 00 00 6c 69 6e 65 4f
0 \| 3 \| 2 \| l i n e O
\| attribute name
-------------------------------------------------
-------------------------------------------------
72 64 65 72 00 6c 69 6e 65 4f 72 64 65 72 00 01
r d e r \\0 \| l i n e O r d e r \\0 \|
\| attribute type \|
-------------------------------------------------
-------------------------------------------------
00 00 00 00 70 69 78 65 6c 41 73 70 65 63 74 52
1 \|INCY \| p i x e l A s p e c t R
attribute size\|value\| attribute name
-------------------------------------------------
-------------------------------------------------
61 74 69 6f 00 66 6c 6f 61 74 00 04 00 00 00 00
a t i o \\0 \| f l o a t \\0 \| 4 \|
\| attribute type \| attribute size \|
-------------------------------------------------
-------------------------------------------------
00 80 3f 73 63 72 65 65 6e 57 69 6e 64 6f 77 43
1.0 \| s c r e e n W i n d o w C
attribute value\| attribute name
-------------------------------------------------
-------------------------------------------------
65 6e 74 65 72 00 76 32 66 00 08 00 00 00 00 00
e n t e r \\0 \| v 2 f \\0 \| 8 \|
\| attribute type \| attribute size \|
-------------------------------------------------
-------------------------------------------------
00 00 00 00 00 00 73 63 72 65 65 6e 57 69 6e 64
0.0 \| 0.0 \| s c r e e n W i n d
attribute value \| attribute name
-------------------------------------------------
-------------------------------------------------
6f 77 57 69 64 74 68 00 66 6c 6f 61 74 00 04 00
o w W i d t h \\0 \| f l o a t \\0 \|
\| attribute type \|
-------------------------------------------------
--------------------------------------------------------
00 00 00 00 80 3f 00 3f 01 00 00 00 00 00 00 5f
4 \| 1.0 \| \\0 \| 319 \|
size \| attribute value \| \| offset of scan line 0 \|
end of header \| start of scan line offset table
--------------------------------------------------------
---------------------------------------------------
01 00 00 00 00 00 00 7f 01 00 00 00 00 00 00 00
351 \| 383 \|
offset of scan line 1 \| offset of scan line 2 \|
end of scan line offset table \|
---------------------------------------------------
-----------------------------------------------------
00 00 00 18 00 00 00 00 00 54 29 d5 35 e8 2d 5c
0 \| 24 \| 0.000 \| 0.042 \| 0.365 \| 0.092 \|
y \| pixel data size \| pixel data for G channel \|
scan line 0
-----------------------------------------------------
-----------------------------------------------------
28 81 3a cf e1 34 3e 8b 0b bb 3d 89 74 f9 3e 01
0.000985395 \| 0.176643 \| 0.0913306 \| 0.487217 \|
pixel data for Z channel \|
\|
-----------------------------------------------------
-----------------------------------------------------
00 00 00 18 00 00 00 37 38 76 33 74 3b 73 38 7f
1 \| 24 \| 0.527 \| 0.233 \| 0.932 \| 0.556 \|
y \| pixel data size \| pixel data for G channel \|
scan line 1
-----------------------------------------------------
-------------------------------------------------
ab e8 3e 8a cf 54 3f 5b 6c 11 3f 20 35 50 3d 02
0.454433 \| 0.831292 \| 0.56806 \| 0.0508319 \|
pixel data for Z channel \|
\|
-------------------------------------------------
-----------------------------------------------------
00 00 00 18 00 00 00 23 3a 0a 34 02 3b 5d 3b 38
2 \| 24 \| 0.767 \| 0.252 \| 0.876 \| 0.920 \|
y \| pixel data size \| pixel data for G channel \|
scan line 2
-----------------------------------------------------
-----------------------------------------------
f3 9a 3c 4d ad 98 3e 1c 14 08 3f 4c f3 03 3f
0.0189148 \| 0.298197 \| 0.531557 \| 0.515431
pixel data for Z channel
end of file
-----------------------------------------------