# 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.