# The Canon RAW (CRW) File Format

This is a description of the Canon CRW file format. CRW files are written in Camera Image File Format (CIFF). The original Canon CIFF specification can be downloaded from http://xyrion.org/ciff/ (which I finally discovered after writing this document!). Note that Canon has three different RAW formats, with newer models producing a TIFF-based CR2 or QuickTime-based CR3 as opposed to the CIFF-based CRW format documented here.

### Comments about the CRW Format

The Canon CRW file format is a joy to work with. It has a structure that is fundamentally similar to TIFF, with directories that point to data within the file. But a major improvement over TIFF is that the offsets are not absolute, they are relative to the start of the data block for each directory. This allows subdirectories within a file to be moved or copied to another file without having to adjust the offsets, which is fantastic because it means that rewriter software doesn't have to understand the complete format in order to be able to successfully rewrite the file.

Also, the data comes before the directories in the file, which is the natural way to write information and minimizes the amount memory needed to buffer the data (unlike EXIF, which is typically the reverse).

> A short rant about TIFF inadequacies:
> TIFF format on the other hand, really sucks in comparison (this includes JPEG too, since JPEG uses TIFF format to store the EXIF information). The main problems are the use of absolute offsets and the ambiguity between integers and pointers (such as those used for custom IFD's). Because absolute offsets require adjusting whenever anything is moved in the file, the format of ALL contained data structures must be understood to properly edit the file. This results in an impossible situation when presented with undocumented custom structures like those used in the maker notes written by modern digital cameras. This is why it is so common for image editors to either scramble the maker notes or discard them completely. The official TIFF recommendation is to discard unknown information when rewriting the image (as Photoshop does), but for many, including myself, this option is simply unacceptable.

The bottom line is that rewriting a Canon CRW file is about 20 times easier, and much less prone to errors than rewriting a TIFF or JPEG.

## CRW (CIFF) Format Specification

### File Header

A Canon CRW file starts with the following byte sequence:

> Offset | Number of bytes | Value | Name | Description
> --- | --- | --- | --- | ---
> 0 | 2 | "II" | ByteOrder | "II" means Intel (little-endian) order, which is the only order I've seen since Canon is using x86 processors in its current cameras, but presumably this could be "MM" for future models.
> 2 | 4 | 0x0000001a | HeaderLength | 32-bit integer giving the length of the CRW file header. For current camera models the header is 26 bytes long.
> 6 | 8 | "HEAPCCDR" | Signature | This series of characters identifies the file as a Canon CRW file. The signature is "HEAPJPGM" for CIFF information in APP0 of JPEG images.
> 14 | 4 | 0x00010002 | CRWVersion | 32-bit integer giving the major (high 16 bits) and minor (low 16 bits) CRW file version numbers. The version is 1.2 for current cameras.
> 18 | 8 | 0 | Reserved | Two 32-bit integers, currently set to zero.

### Directory Block Structure

The root directory block begins immediately after the file header (at the position specified by HeaderLength), and ends at the end of the file. The structure of this block is as follows:

> Offset within block | Number of bytes | Value | Name | Description
> --- | --- | --- | --- | ---
> 0 | S | - - - - - | ValueData | The value data referenced by offsets in the directory
> S | 2 | N | DirCount | 16-bit integer giving the number of directory entries
> S + 2 | N * 10 | - - - | DirEntries | The CRW directory entries
> S + 2 + N*10 | any | - | OtherData | (be aware there may be other data hiding here)
> BlockSize - 4 | 4 | S | DirStart | 32-bit integer giving the size of the ValueData

To parse a CRW directory block, first read the 4 bytes at the end of the block to get the location (S) of DirCount. Next read DirCount to determine the number of entries (N) in the directory, then read the directory entries.

The ValueData may contain complete subdirectory blocks, each of which has the same format as specified above (and these subdirectories may themselves contain sub-subdirectories...). For these subdirectories, BlockSize is given by the Size specified in the corresponding directory entry. For the root directory, BlockSize is the length of the file.

The OtherData normally does not exist (eg. the DirEntries usually end at the DirStart pointer), but this is not always the case: Canon Digital Photo Professional uses this area in the root directory block to store VRD data in edited CRW images. (Note that VRD supports embedded XMP, which provides a technique to store modern metadata in CRW images!)

### CRW Directory Entry Format

The CRW directory consists of N 10-byte entries. The format of each entry is as follows:

> Offset within entry | Number of bytes | Name | Description
> --- | --- | --- | ---
> 0 | 2 | Tag | 16-bit integer identifying the type of data
> 2 | 4 | Size | 32-bit integer giving the number of bytes in the value data
> 6 | 4 | Offset | 32-bit integer offset that gives the number of bytes from the start of the ValueData block to the start of the value data for this directory entry

Data values with lengths shorter than 8 bytes may be stored in the directory Size and Offset fields. For these values the DataLocation bits in the Tag are set to 0x4000 (see DataLocation table below).

Data stored in the ValueData block must be aligned on even 2-byte boundaries, yielding Offsets which are divisible by 2. To achieve this, records with an odd number of bytes must be padded with a zero byte.

### Tag Bits

The 16-bit Tag value is composed of 3 bit fields, as follows:

> Bits | Mask | Name | Description
> --- | --- | --- | ---
> 14-15 | 0xc000 | DataLocation | Specifies the location of the data
> 11-13 | 0x3800 | DataFormat | Identifies the information format
> 0-10 | 0x07ff | TagIndex | Index to identify the specific type of information

#### DataLocation

Value data may either be stored in the ValueData block, or within the Size and Offset fields of the directory entry if it is less than 8 bytes long. The DataLocation bits specify where the value is stored:

> DataLocation | Where | Description
> --- | --- | ---
> 0x0000 | ValueData | Values are stored in the ValueData block, at the specified Offset and Size
> 0x4000 | Directory | Values are stored in the Size and Offset fields of the directory entry. Values stored here are limited to a maximum size of 8 bytes.
> 0x8000 0xc000 | ? | -

#### DataFormat

Three Tag bits are used to specify the data format:

> DataFormat | Alignment | Description
> --- | --- | ---
> 0x0000 | 1-Byte | A series of bytes
> 0x0800 | 1-Byte | A null-terminated ASCII string
> 0x1000 | 2-Byte | A series of 16-bit integers
> 0x1800 | 4-Byte | A series of 32-bit integers or floats
> 0x2000 | 1-Byte | A structure which is a mixture of formats
> 0x2800 0x3000 | 1-Byte | A subdirectory block
> 0x3800 | ? | -

#### TagID = DataFormat + TagIndex

Together, the DataFormat and TagIndex fields form a TagID which can be used to identify tags within the CRW file. The following is a list of known TagID values and their corresponding tag numbers in the EXIF maker notes when found in a JPEG or TIFF image. Also listed is the TagID of the SubDirectory where the information is found. The Size listed below is an observed size of the value data, and is not necessarily expected to remain constant for all camera models.

> TagID | EXIF | SubDir | Name | Size | Description
> --- | --- | --- | --- | --- | ---
> 1-Byte Alignment
> 0x0000 | - | any | NullRecord | 0 | This is a null directory entry
> 0x0001 | - | any | FreeBytes | varies | Unused bytes in the ValueData
> 0x0006 | - | 0x300b | - | 8 | -
> 0x0032 | - | 0x300b | CanonColorInfo1 | 768 or 2048 | Block of color information (format unknown)
> 0x0036 | - | 0x300b | ? | varies | -
> 0x003f | - | 0x300b | ? | 5120 | -
> 0x0040 | - | 0x300b | ? | 256 | -
> 0x0041 | - | 0x300b | ? | 256 | -
> ASCII Strings
> 0x0805 | - | 0x2804 | CanonFileDescription | 32 | Description of the file format. eg) "EOS DIGITAL REBEL CMOS RAW"
> 0x0805 | - | 0x300a | UserComment | 256 | User comment (usually blank)
> 0x080a | - | 0x2807 | CanonRawMakeModel | 32 | Two end-to-end null-terminated ASCII strings giving the camera make and model. eg) "Canon","Canon EOS DIGITAL REBEL"
> 0x080b | 0x07 | 0x3004 | CanonFirmwareVersion | 32 | Firmware version. eg) "Firmware Version 1.1.1"
> 0x080c | - | ? | ComponentVersion | ? | -
> 0x080d | - | 0x3004 | ROMOperationMode | 4 | eg) The string "USA" for 300D's sold in North America
> 0x0810 | 0x09 | 0x2807 | OwnerName | 32 | Owner's name. eg) "Phil Harvey"
> 0x0815 | 0x06 | 0x2804 | CanonImageType | 32 | Type of file. eg) "CRW:EOS DIGITAL REBEL CMOS RAW"
> 0x0816 | - | 0x300a | OriginalFileName | 32 | Original file name. eg) "CRW_1834.CRW"
> 0x0817 | - | 0x300a | ThumbnailFileName | 32 | Thumbnail file name. eg) "CRW_1834.THM"
> 2-Byte Alignment
> 0x100a | - | 0x300a | TargetImageType | 2 | 0=real-world subject, 1=written document
> 0x1010 | - | 0x3002 | ShutterReleaseMethod | 2 | 0=single shot, 1=continuous shooting
> 0x1011 | - | 0x3002 | ShutterReleaseTiming | 2 | 0=priority on shutter, 1=priority on focus
> 0x1014 | - | 0x3002 | - | 8 | -
> 0x1016 | - | 0x3002 | ReleaseSetting | 2 | -
> 0x101c | - | 0x3004 | BaseISO | 2 | The camera body's base ISO sensitivity
> 0x1026 | - | 0x300a | - | 6 | -
> 0x1028 | 0x03 | 0x300b | CanonFlashInfo? | 8 | Unknown information, flash related
> 0x1029 | 0x02 | 0x300b | FocalLength | 8 | Four 16 bit integers: 0) unknown, 1) focal length in mm, 2-3) sensor width and height in units of 1/1000 inch
> 0x102a | 0x04 | 0x300b | CanonShotInfo | varies | Data block giving shot information
> 0x102c | - | 0x300b | CanonColorInfo2 | 256 | Data block of color information (format unknown)
> 0x102d | 0x01 | 0x300b | CanonCameraSettings | varies | Data block giving camera settings
> 0x1030 | - | 0x300b | WhiteSample | 102 or 118 | White sample information with encrypted 8x8 sample data
> 0x1031 | - | 0x300b | SensorInfo | 34 | Sensor size and resolution information
> 0x1033 | 0x0f | 0x300b | CanonCustomFunctions | varies | Data block giving Canon custom settings
> 0x1038 | 0x12 | 0x300b | CanonAFInfo | varies | Data block giving AF-specific information
> 0x1039 | 0x13 | 0x300b | ? | 8 | -
> 0x103c | - | 0x300b | ? | 156 | -
> 0x107f | - | 0x300b | - | varies | -
> 0x1093 | 0x93 | 0x300b | CanonFileInfo | 18 | Data block giving file-specific information
> 0x10a8 | 0xa8 | 0x300b | ? | 20 | -
> 0x10a9 | 0xa9 | 0x300b | ColorBalance | 82 | Table of 16-bit integers. The first integer (like many other data blocks) is the number of bytes in the record. This is followed by red, green1, green2 and blue levels for WhiteBalance settings: auto, daylight, shade, cloudy, tungsten, fluorescent, flash, custom and kelvin. The final 4 entries appear to be some sort of baseline red, green1, green2 and blue levels.
> 0x10aa | 0xaa | 0x300b | ? | 10 | -
> 0x10ad | - | 0x300b | ? | 62 | -
> 0x10ae | 0xae | 0x300b | ColorTemperature | 2 | 16-bit integer giving the color temperature
> 0x10af | - | 0x300b | ? | 2 | -
> 0x10b4 | 0xb4 | 0x300b | ColorSpace | 2 | 16-bit integer specifying the color space (1=sRGB, 2=Adobe RGB, 0xffff=uncalibrated)
> 0x10b5 | 0xb5 | 0x300b | RawJpgInfo | 10 | Data block giving embedded JPG information
> 0x10c0 | 0xc0 | 0x300b | ? | 26 | -
> 0x10c1 | 0xc1 | 0x300b | ? | 26 | -
> 0x10c2 | - | 0x300b | ? | 884 | -
> 4-Byte Alignment
> 0x1803 | - | 0x300a | ImageFormat | 8 | 32-bit integer specifying image format (0x20001 for CRW), followed by 32-bit float giving target compression ratio
> 0x1804 | - | 0x300a | RecordID | 4 | The number of pictures taken since the camera was manufactured
> 0x1805 | - | 0x3002 | - | 8 | -
> 0x1806 | - | 0x3002 | SelfTimerTime | 4 | 32-bit integer giving self-timer time in milliseconds
> 0x1807 | - | 0x3002 | TargetDistanceSetting | 4 | 32-bit float giving target distance in mm
> 0x180b | 0x0c | 0x3004 | SerialNumber | 4 | The camera body number for EOS models. eg) 00560012345
> 0x180e | - | 0x300a | TimeStamp | 12 | 32-bit integer giving the time in seconds when the picture was taken, followed by a 32-bit timezone in seconds
> 0x1810 | - | 0x300a | ImageInfo | 28 | Data block containing image information, including rotation
> 0x1812 | - | 0x3004 | - | 40 | -
> 0x1813 | - | 0x3002 | FlashInfo | 8 | Two 32-bit floats: The flash guide number and the flash threshold
> 0x1814 | - | 0x3003 | MeasuredEV | 4 | 32-bit float giving the measured EV
> 0x1817 | 0x08 | 0x300a | FileNumber | 4 | 32-bit integer giving the number of this file. eg) 1181834
> 0x1818 | - | 0x3002 | ExposureInfo | 12 | Three 32-bit floats: Exposure compensation, Tv, Av
> 0x1819 | - | 0x300b | - | 64 | -
> 0x1834 | 0x10 | 0x300b | CanonModelID | 4 | Unsigned 32-bit integer giving unique model ID
> 0x1835 | - | 0x300b | DecoderTable | 16 | RAW decoder table information
> 0x183b | 0x15 | 0x300b | SerialNumberFormat | 4 | 32-bit integer (0x90000000=format 1, 0xa0000000=format 2)
> Mixed Data Records
> 0x2005 | - | root | RawData | varies | The raw data itself (the bulk of the CRW file)
> 0x2007 | - | root | JpgFromRaw | varies | The embedded JPEG image (2048x1360 pixels for the 300D with Canon firmware)
> 0x2008 | - | root | ThumbnailImage | varies | Thumbnail image (JPEG, 160x120 pixels)
> SubDirectory Blocks
> 0x2804 | - | 0x300a | ImageDescription | varies | The image description subdirectory
> 0x2807 | - | 0x300a | CameraObject | varies | The camera object subdirectory
> 0x3002 | - | 0x300a | ShootingRecord | varies | The shooting record subdirectory
> 0x3003 | - | 0x300a | MeasuredInfo | varies | The measured information subdirectory
> 0x3004 | - | 0x2807 | CameraSpecification | varies | The camera specification subdirectory
> 0x300a | - | root | ImageProps | varies | The main subdirectory containing all meta information
> 0x300b | - | 0x300a | ExifInformation | varies | The subdirectory containing most of the JPEG/TIFF EXIF information

### Revisions

Mar. 21, 2018 - Added mention of the CR3 file format

Sep. 20, 2010 - Added note about XMP support in the VRD data

Feb. 12, 2009 - Moved a couple of entries in the TagID table that were in the wrong section

Feb. 4, 2008 - Added a number of unknown TagID's, decode some tags in the WhiteSample and DecoderTable data blocks, and fix incorrect SubDir for SerialNumber tag

Nov. 16, 2007 - Added a number of unknown blocks

Sep. 12, 2007 - Change name of CanonPictureInfo record to CanonAFInfo

Nov. 28, 2006 - Highlight the possibility of OtherData existing in the directory block

Please e-mail me if you find any errors or omissions in this document. My address is philharvey66 at gmail.com - Thanks!

Created Jan. 28, 2005
Last revised Mar. 21, 2018

<-- Back to ExifTool home page