CUPS Raster Format

CUPS raster files are device-dependent raster image files that contain a PostScript page device dictionary and device-dependent raster imagery for each page in the document. These files are used to transfer raster data from the PostScript and image file RIPs to device-dependent filters that convert the raster data to a printable format.

CUPS 1.0 and 1.1 used a version 1 raster format. CUPS 1.2 introduced version 2 (compressed) and version 3 (uncompressed) formats that are a superset of the version 1 format. Applications using the CUPS Imaging API (the cupsRaster* functions) can read all formats without code changes.

The registered MIME media type for CUPS raster files is application/vnd.cups-raster.

Version 1 Raster File Format

A version 1 raster file begins with a 32-bit synchronization word: 0x52615374 ("RaSt") for big-endian architectures and 0x74536152 ("tSaR") for little-endian architectures. The writer of the raster file will use the native word order, and the reader is responsible for detecting a reversed word order file and swapping bytes as needed. The CUPS Imaging API raster functions perform this function automatically.

Following the synchronization word are a series of raster pages. Each page starts with a page device dictionary header and is followed immediately by the (uncompressed, raw) raster data for that page.

Table 1: CUPS Version 1 Raster Page Device Dictionary
Bytes	Type	Description	Values
0-63	C String	MediaClass	Media class string
64-127	C String	MediaColor	Media color string
128-191	C String	MediaType	Media type string
192-255	C String	OutputType	Output type string
256-259	Unsigned Integer	AdvanceDistance	0 to 2³² - 1 points
260-263	Unsigned Integer	AdvanceMedia	0 = Never advance roll 1 = Advance roll after file 2 = Advance roll after job 3 = Advance roll after set 4 = Advance roll after page
264-267	Unsigned Integer	Collate	0 = do not collate copies 1 = collate copies
268-271	Unsigned Integer	CutMedia	0 = Never cut media 1 = Cut roll after file 2 = Cut roll after job 3 = Cut roll after set 4 = Cut roll after page
272-275	Unsigned Integer	Duplex	0 = Print single-sided 1 = Print double-sided
276-283	Unsigned Integers (2)	HWResolution	Horizontal and vertical resolution in dots-per-inch.
284-299	Unsigned Integers (4)	ImagingBoundingBox	Four integers giving the left, bottom, right, and top positions of the page bounding box in points
300-303	Unsigned Integer	InsertSheet	0 = Do not insert separator sheets 1 = Insert separator sheets
304-307	Unsigned Integer	Jog	0 = Do no jog pages 1 = Jog pages after file 2 = Jog pages after job 3 = Jog pages after set
308-311	Unsigned Integer	LeadingEdge	0 = Top edge is first 1 = Right edge is first 2 = Bottom edge is first 3 = Left edge is first
312-319	Unsigned Integers (2)	Margins	Left and bottom origin of image in points
320-323	Unsigned Integer	ManualFeed	0 = Do not manually feed media 1 = Manually feed media
324-327	Unsigned Integer	MediaPosition	Input slot position from 0 to N
328-331	Unsigned Integer	MediaWeight	Media weight in grams per meter squared
332-335	Unsigned Integer	MirrorPrint	0 = Do not mirror prints 1 = Mirror prints
336-339	Unsigned Integer	NegativePrint	0 = Do not invert prints 1 = Invert prints
340-343	Unsigned Integer	NumCopies	1 to 2³² - 1
344-347	Unsigned Integer	Orientation	0 = Do not rotate page 1 = Rotate page counter-clockwise 2 = Turn page upside down 3 = Rotate page clockwise
348-351	Unsigned Integer	OutputFaceUp	0 = Output face down 1 = Output face up
352-359	Unsigned Integers (2)	PageSize	Width and length in points
360-363	Unsigned Integer	Separations	0 = Print composite image 1 = Print color separations
364-367	Unsigned Integer	TraySwitch	0 = Do not change trays if selected tray is empty 1 = Change trays if selected tray is empty
368-371	Unsigned Integer	Tumble	0 = Do not rotate even pages when duplexing 1 = Rotate even pages when duplexing
372-375	Unsigned Integer	cupsWidth	Width of page image in pixels
376-379	Unsigned Integer	cupsHeight	Height of page image in pixels
380-383	Unsigned Integer	cupsMediaType	Driver-specific 0 to 2³² - 1
384-387	Unsigned Integer	cupsBitsPerColor	1, 2, 4, 8 bits for version 1 raster files 1, 2, 4, 8, and 16 bits for version 2 raster files
388-391	Unsigned Integer	cupsBitsPerPixel	1 to 32 bits for version 1 raster files 1 to 64 bits for version 2 raster files
392-395	Unsigned Integer	cupsBytesPerLine	1 to 2³² - 1 bytes
396-399	Unsigned Integer	cupsColorOrder	0 = chunky pixels (CMYK CMYK CMYK) 1 = banded pixels (CCC MMM YYY KKK) 2 = planar pixels (CCC... MMM... YYY... KKK...)
400-403	Unsigned Integer	cupsColorSpace	0 = white (sRGB) 1 = RGB (sRGB) 2 = RGBA (sRGB) 3 = black 4 = CMY 5 = YMC 6 = CMYK 7 = YMCK 8 = KCMY 9 = KCMYcm 10 = GMCK 11 = GMCS 12 = WHITE 13 = GOLD 14 = SILVER 15 = CIE XYZ 16 = CIE Lab 17 = RGBW (sRGB) 32 = ICC1 (CIE Lab with hint for 1 color) 33 = ICC2 (CIE Lab with hint for 2 colors) 34 = ICC3 (CIE Lab with hint for 3 colors) 35 = ICC4 (CIE Lab with hint for 4 colors) 36 = ICC5 (CIE Lab with hint for 5 colors) 37 = ICC6 (CIE Lab with hint for 6 colors) 38 = ICC7 (CIE Lab with hint for 7 colors) 39 = ICC8 (CIE Lab with hint for 8 colors) 40 = ICC9 (CIE Lab with hint for 9 colors) 41 = ICCA (CIE Lab with hint for 10 colors) 42 = ICCB (CIE Lab with hint for 11 colors) 43 = ICCC (CIE Lab with hint for 12 colors) 44 = ICCD (CIE Lab with hint for 13 colors) 45 = ICCE (CIE Lab with hint for 14 colors) 46 = ICCF (CIE Lab with hint for 15 colors)
404-407	Unsigned Integer	cupsCompression	Driver-specific 0 to 2³² - 1
408-411	Unsigned Integer	cupsRowCount	Driver-specific 0 to 2³² - 1
412-415	Unsigned Integer	cupsRowFeed	Driver-specific 0 to 2³² - 1
416-419	Unsigned Integer	cupsRowStep	Driver-specific 0 to 2³² - 1

Version 2 Raster File Format

A version 2 raster file begins with a 32-bit synchronization word: 0x52615332 ("RaS2") for big-endian architectures and 0x32536152 ("2SaR") for little-endian architectures. The writer of the raster file will use the native word order, and the reader is responsible for detecting a reversed word order file and swapping bytes as needed. The CUPS Imaging API raster functions perform this function automatically.

Following the synchronization word are a series of raster pages. Each page starts with a version 2 page device dictionary header and is followed immediately by the compressed raster data for that page.

Table 2: CUPS Version 2 Raster Page Device Dictionary
Bytes	Type	Description	Values
0-419	Version 1 header data	See Table 1
420-423	Unsigned Integer	cupsNumColors	1 to 6 colors
424-427	IEEE Single Precision	cupsBorderlessScalingFactor	0.0 or 1.0 or greater
428-435	IEEE Single Precision (2)	cupsPageSize	Width and length in points
436-451	IEEE Single Precision (4)	cupsImagingBBox	Four floating point numbers giving the left, bottom, right, and top positions of the page bounding box in points
452-515	Unsigned Integers (16)	cupsInteger	16 driver-defined integer values
516-579	IEEE Single Precision (16)	cupsReal	16 driver-defined floating point values
580-1603	C Strings (16x64)	cupsString	16 driver-defined strings
1604-1667	C String	cupsMarkerType	Ink/toner type string
1668-1731	C String	cupsRenderingIntent	Color rendering intent string
1732-1795	C String	cupsPageSizeName	Page size name/keyword string from PPD

Compressed Raster Data Format

The version 2 raster data is compressed using a modified TIFF packbits algorithm. Lines are grouped into an integral number of color values based upon the cupsColorOrder setting:

Table 3: Color Value Sizes
cupsColorOrder	Bytes per color value
0 (chunky)	(`cupsBitsPerPixel` + 7) / 8
1 (banded)	(`cupsBitsPerColor` + 7) / 8
2 (planar)	(`cupsBitsPerColor` + 7) / 8

Each line of raster data begins with a repetition count from 1 to 256 that is encoded using a single byte of "count - 1".

After the repetition count, whole color values for that line are run-length encoded using the TIFF packbits algorithm. 1 to 128 repeated colors are encoded using an initial byte of "count - 1" followed by the color value byte(s). 2 to 128 non-repeating colors are encoded using an initial byte of "257 - count" followed by the color value bytes.

Version 3 Raster File Format

A version 3 raster file begins with a 32-bit synchronization word: 0x52615333 ("RaS3") for big-endian architectures and 0x33536152 ("3SaR") for little-endian architectures. The writer of the raster file will use the native word order, and the reader is responsible for detecting a reversed word order file and swapping bytes as needed. The CUPS Imaging API raster functions perform this function automatically.

Following the synchronization word are a series of raster pages. Each page starts with a version 2 page device dictionary header and is followed immediately by the uncompressed raster data for that page.

Pixel Value Coding

The following sections describe the encoding and decoding of the color values in a CUPS raster file. In general, colors are packed into the minimum number of bytes, with special consideration provided for efficiency of encoding and access. Multi-byte values are stored in the native byte order and automatically swapped as needed when reading them using the CUPS imaging API.

CUPS_ORDER_CHUNKED

The chunked order provides the pixel value packed in a single place. Pixel values with 8 or more bits per color are stored as an array of colors in order, e.g. for CUPS_CSPACE_RGB you will see 8/16-bits of red, then blue, then green, then red, green, blue, etc. Pixel values with less than 8 bits per color are packed together as shown in Table 4. Multi-byte pixel values are stored in the native word order, just as for 16-bit color values.

Table 4: Chunked Color Values
Bits	1-color	3-color	4-color	6-color
1	W/W/W/W/W/W/W/W	0RGB/0RGB	CMYK/CMYK	00KCMYcm
2	WW/WW/WW/WW	00RRGGBB	CCMMYYKK	N/A
4	WWWW/WWWW	0000RRRRGGGGBBBB (multi-byte)	CCCCMMMMYYYYKKKK (multi-byte)	N/A

CUPS_ORDER_BANDED

The banded order provides each color as a separate line of data. Each color plane for a line is written in sequence, e.g. for the CUPS_CSPACE_CMYK colorspace you would see all of the cyan pixels for a line followed by the magenta, yellow, and black pixels for that line. This is repeated for all of the lines on the page. Color values are packed starting with the most-significant bit (MSB) first.

CUPS_ORDER_PLANAR

The planar order provides each color as a separate page of data using a shared page header. Each color plane for a page is written in sequence, e.g. for the CUPS_CSPACE_CMYK colorspace you would see all of the cyan pixels for a page followed by the magenta, yellow, and black pixels for that page. Color values are packed starting with the most-significant bit (MSB) first. Each line starts on an 8-bit boundary.

CUPS_CSPACE_W, CUPS_CSPACE_RGB, CUPS_CSPACE_RGBA, and CUPS_CSPACE_RGBW

These colorspaces use the sRGB colorspace definition and whitepoint.

CUPS_CSPACE_KCMYcm

When cupsBitsPerColor is 1, 6 color planes are provided - black, cyan, magenta, yellow, light cyan, and light magenta. When cupsBitsPerColor is greater than 1, 4 color planes are provided using the CUPS_CSPACE_KCMY colorspace instead.

When cupsColorOrder is CUPS_ORDER_CHUNKED, bit 5 corresponds to black and bit 0 corresponds to light magenta. For CUPS_ORDER_BANDED and CUPS_ORDER_PLANAR, each color plane is encoded separately.

CUPS_CSPACE_CIELab and CUPS_CSPACE_ICCn

These colorspaces map a CIE Lab color value with a D65 whitepoint to either a 8- or 16-bit per color chunked (CUPS_ORDER_CHUNKED) format; the banded (CUPS_ORDER_BANDED) and planar (CUPS_ORDER_PLANAR) color orders are not supported.

The values are encoded and decoded using the following formulas:

8-bit Encoding:
L8 = 2.55 * L + 0.5
a8 = a + 128.5
b8 = b + 128.5
8-bit Decoding:
L = L8 / 2.55
a = a8 - 128
b = b8 - 128
16-bit Encoding:
L16 = 655.35 * L + 0.5
a16 = 256 * (a + 128) + 0.5
b16 = 256 * (b + 128) + 0.5
16-bit Decoding:
L = L16 / 655.35
a = a16 / 256 - 128
b = b16 / 256 - 128

CUPS_CSPACE_CIEXYZ

These colorspaces map a CIE XYZ color value with a D65 whitepoint to either a 8- or 16-bit per color chunked (CUPS_ORDER_CHUNKED) format; the banded (CUPS_ORDER_BANDED) and planar (CUPS_ORDER_PLANAR) color orders are not supported.

The values are encoded and decoded using the following formulas:

8-bit Encoding:
X8 = 231.8181 * X + 0.5
Y8 = 231.8181 * Y + 0.5
Z8 = 231.8181 * Z + 0.5
8-bit Decoding:
X = X8 / 231.8181
Y = Y8 / 231.8181
Z = Z8 / 231.8181
16-bit Encoding:
X16 = 59577.2727 * X + 0.5
Y16 = 59577.2727 * Y + 0.5
Z16 = 59577.2727 * Z + 0.5
16-bit Decoding:
X = X16 / 59577.2727
Y = Y16 / 59577.2727
Z = Z16 / 59577.2727

The scaling factor for XYZ values is 1/1.1, or 231.8181 for 8-bit values and 59577.2727 for 16-bit values. This allows for a slight overflow of XYZ values when converting from RGB, improving accuracy.

Change History

Changes in CUPS 1.2.2

Added version 3 (uncompressed) format.

Changes in CUPS 1.2.1

Added new sections on coding pixel values.
Clarified definitions of color spaces.

Changes in CUPS 1.2

Bumped raster version to 2
Added RGBW colorspace
Added 16 bit per color support
Added cupsNumColors, cupsBorderlessScalingFactor, cupsPageSize, cupsImagingBBox, cupsInteger, cupsReal, cupsString, cupsMarkerType, cupsRenderingIntent, and cupsPageSizeName attributes to the page device dictionary
Added raster data compression
Added data type column to device dictionary documentation.

Changes in CUPS 1.1.19

Added ICC and CIE colorspaces.