The Canon RAW (CRW) File Format

This is a description of the Canon CRW file format. CRW files are written in CIFF format. The original Canon CIFF documentation can be downloaded from http://xyrion.org/ciff/ (which I finally discovered after writing this document!). Note that Canon uses two different RAW formats, and some camera models produce CR2 instead of CRW files. The CR2 files use a TIFF format, which is different than the CRW CIFF 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 the EXIF standard which is 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. In fact, EXIF is worse because it specifies that the value data comes AFTER the directory information, which by design requires all offsets to be fixed up after the length of the directory is known... grrr.) So re-writing a TIFF file is a major pain in the butt -- all offsets require adjusting whenever anything is moved in the file, and to do this properly the software must understand the format of ALL contained data structures to be able to adjust embedded offsets. This presents a near impossible situation because of structures like the maker notes where the format is undocumented and varies for different camera models. This is why most of the software out there that can rewrite a TIFF or JPEG file will scramble the maker notes!

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.

4 4 0x0000001a BlockStart 32-bit integer giving the offset from the start of the file to the start of the root directory block. This value may change for future camera models.

8 8 "HEAPCCDR" Signature This series of characters identifies the file as a Canon CRW file.

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.
4	4	0x0000001a	BlockStart	32-bit integer giving the offset from the start of the file to the start of the root directory block. This value may change for future camera models.
8	8	"HEAPCCDR"	Signature	This series of characters identifies the file as a Canon CRW file.

Directory Block Structure

The root directory block begins at the offset specified in the file header, and ends at the end of the file. The structure of the 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

BlockSize - 4 4 S DirStart 32-bit integer giving the size of the ValueData

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
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 of DirCount. Next read DirCount to determine the number of entries 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...).

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

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

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 ? -

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 ? -

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

0x0032 - 0x300b CanonColorInfo1 2048 Block of color information (format unknown)

ASCII Strings

0x0805 0x0d 0x2804 CanonFileDescription 32 Description of the file format. ie) "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. ie) "Canon","Canon EOS DIGITAL REBEL"

0x080b 0x07 0x3004 CanonFirmwareVersion 32 Firmware version. ie) "Firmware Version 1.1.1"

0x080c - ? ComponentVersion ? -

0x080d - 0x3004 ROMOperationMode 4 ie) The string "USA" for 300D's sold in North America

0x0810 0x09 0x2807 OwnerName 32 Owner's name. ie) "Phil Harvey"

0x0815 0x06 0x2804 CanonImageType 32 Type of file. ie) "CRW:EOS DIGITAL REBEL CMOS RAW"

0x0816 - 0x300a OriginalFileName 32 Original file name. ie) "CRW_1834.CRW"

0x0817 - 0x300a ThumbnailFileName 32 Thumbnail file name. ie) "CRW_1834.THM"

2-Byte Alignment

0x100a - 0x300a TargetImageType 2 -

0x1010 - 0x3002 ShutterReleaseMethod 2 0=single shot, 1=continuous shooting

0x1011 - 0x3002 ShutterReleaseTiming 2 0=priority on shutter, 1=priority on focus

0x1016 - 0x3002 ReleaseSetting 2 -

0x101c - 0x3004 BaseISO 2 The camera body's base ISO sensitivity

0x1028 0x03 ? ? ? -

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 - ? CanonColorInfo2 ? Data block of color information (format unknown)

0x102d 0x01 0x300b CanonCameraSettings 92 Data block giving camera settings

0x1031 - 0x300b SensorInfo 34 Sensor size and resolution information

0x1033 0x0f 0x300b CanonCustomFunctions Varies Data block giving Canon custom settings

0x1038 0x12 0x300b CanonPictureInfo Varies Data block giving picture-specific information

0x1039 0x13 0x300b ? 8 -

0x1093 0x93 0x300b ? 18 -

0x10a8 0xa8 0x300b ? 20 -

0x10a9 0xa9 0x300b WhiteBalanceTable 82 Table of red/blue balance levels for all WhiteBalance menu entries, as a series of 16-bit integers which are combined in pairs to form rational values

0x10aa 0xaa 0x300b ? 10 -

0x10ae 0xae 0x300b ColorTemperature 2 16-bit integer giving the color temperature

0x10b4 0xb4 0x300b ColorSpace 2 16-bit integer specifying the color space (1=sRGB, 2=Adobe RGB, 0xffff=uncalibrated)

0x10b5 0xb5 0x300b ? 10 -

0x10c0 0xc0 0x300b ? 26 -

0x10c1 0xc1 0x300b ? 26 -

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

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 0x2807 SerialNumber 4 The camera body number. ie) 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

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. ie) 1181834

0x1818 - 0x3002 ExposureInfo 12 Three 32-bit floats: Exposure compensation, Tv, Av

0x1834 0x10 ? ? ? -

0x1835 - 0x300b DecoderTable 16 RAW decoder table

0x183b 0x15 0x300b ? 4 ? (observed with a value of 0x90000000)

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

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
0x0032	-	0x300b	CanonColorInfo1	2048	Block of color information (format unknown)
ASCII Strings
0x0805	0x0d	0x2804	CanonFileDescription	32	Description of the file format. ie) "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. ie) "Canon","Canon EOS DIGITAL REBEL"
0x080b	0x07	0x3004	CanonFirmwareVersion	32	Firmware version. ie) "Firmware Version 1.1.1"
0x080c	-	?	ComponentVersion	?	-
0x080d	-	0x3004	ROMOperationMode	4	ie) The string "USA" for 300D's sold in North America
0x0810	0x09	0x2807	OwnerName	32	Owner's name. ie) "Phil Harvey"
0x0815	0x06	0x2804	CanonImageType	32	Type of file. ie) "CRW:EOS DIGITAL REBEL CMOS RAW"
0x0816	-	0x300a	OriginalFileName	32	Original file name. ie) "CRW_1834.CRW"
0x0817	-	0x300a	ThumbnailFileName	32	Thumbnail file name. ie) "CRW_1834.THM"
2-Byte Alignment
0x100a	-	0x300a	TargetImageType	2	-
0x1010	-	0x3002	ShutterReleaseMethod	2	0=single shot, 1=continuous shooting
0x1011	-	0x3002	ShutterReleaseTiming	2	0=priority on shutter, 1=priority on focus
0x1016	-	0x3002	ReleaseSetting	2	-
0x101c	-	0x3004	BaseISO	2	The camera body's base ISO sensitivity
0x1028	0x03	?	?	?	-
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	-	?	CanonColorInfo2	?	Data block of color information (format unknown)
0x102d	0x01	0x300b	CanonCameraSettings	92	Data block giving camera settings
0x1031	-	0x300b	SensorInfo	34	Sensor size and resolution information
0x1033	0x0f	0x300b	CanonCustomFunctions	Varies	Data block giving Canon custom settings
0x1038	0x12	0x300b	CanonPictureInfo	Varies	Data block giving picture-specific information
0x1039	0x13	0x300b	?	8	-
0x1093	0x93	0x300b	?	18	-
0x10a8	0xa8	0x300b	?	20	-
0x10a9	0xa9	0x300b	WhiteBalanceTable	82	Table of red/blue balance levels for all WhiteBalance menu entries, as a series of 16-bit integers which are combined in pairs to form rational values
0x10aa	0xaa	0x300b	?	10	-
0x10ae	0xae	0x300b	ColorTemperature	2	16-bit integer giving the color temperature
0x10b4	0xb4	0x300b	ColorSpace	2	16-bit integer specifying the color space (1=sRGB, 2=Adobe RGB, 0xffff=uncalibrated)
0x10b5	0xb5	0x300b	?	10	-
0x10c0	0xc0	0x300b	?	26	-
0x10c1	0xc1	0x300b	?	26	-
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
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	0x2807	SerialNumber	4	The camera body number. ie) 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
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. ie) 1181834
0x1818	-	0x3002	ExposureInfo	12	Three 32-bit floats: Exposure compensation, Tv, Av
0x1834	0x10	?	?	?	-
0x1835	-	0x300b	DecoderTable	16	RAW decoder table
0x183b	0x15	0x300b	?	4	? (observed with a value of 0x90000000)
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

Please e-mail me if you find any errors or omissions in this document. My address is phil at owl.phy.queensu.ca - Thanks!

P. Harvey - Last revised Apr. 2, 2005