DRAFT TIFF Technical Note #2 17-Mar-95 ============================ This Technical Note describes serious problems that have been found in TIFF 6.0's design for embedding JPEG-compressed data in TIFF (Section 22 of the TIFF 6.0 spec of 3 June 1992). A replacement TIFF/JPEG specification is given. Some corrections to Section 21 are also given. To permit TIFF implementations to continue to read existing files, the 6.0 JPEG fields and tag values will remain reserved indefinitely. However, TIFF writers are strongly discouraged from using the 6.0 JPEG design. It is expected that the next full release of the TIFF specification will not describe the old design at all, except to note that certain tag numbers are reserved. The existing Section 22 will be replaced by the specification text given in the second part of this Tech Note. Problems in TIFF 6.0 JPEG ========================= Abandoning a published spec is not a step to be taken lightly. This section summarizes the reasons that have forced this decision. TIFF 6.0's JPEG design suffers from design errors and limitations, ambiguities, and unnecessary complexity. Design errors and limitations ----------------------------- The fundamental design error in the existing Section 22 is that JPEG's various tables and parameters are broken out as separate fields which the TIFF control logic must manage. This is bad software engineering: that information should be treated as private to the JPEG codec (compressor/decompressor). Worse, the fields themselves are specifiedR>Class B for bilevel images SamplesPerPixel = 1
BitsPerSample = 1
Compression = 1 (none), 2 (CCITT 1D), or 32773 (PackBits)
PhotometricInterpretation = 0 (Min-is-White), 1 (Min-is-Black)
Class G for grayscale images SamplesPerPixel = 1
BitsPerSample = 4, 8
Compression = 1 (none) 5 (LZW)
PhotometricInterpretation = 0 (Min-is-White), 1 (Min-is-Black)
Class P for palette color images SamplesPerPixel = 1
BitsPerSample = 1-8
Compression = 1 (none) 5 (LZW)
PhotometricInterpretation = 3 (Palette RGB)
ColorMapClass R for RGB full color images SamplesPerPixel = 3
BitsPerSample = <8,8,8>
PlanarConfiguration = 1, 2
Compression = 1 (none) 5 (LZW)
PhotometricInterpretation = 2 (RGB)
Class F for facsimile (Class B tags plus...)
Compression = 3 (CCITT Group 3), 4 (CCITT Group 4)
FillOrder = 1 (MSB), 2 (LSB)
Group3Options = 1 (2d encoding), 4 (zero fill), 5 (2d+fill)
ImageWidth = 1728, 2048, 2482
NewSubFileType = 2
ResolutionUnit = 2 (Inch), 3 (Centimeter)
PageNumber, XResolution, YResolution, Software, BadFaxLines, CleanFaxData, ConsecutiveBadFaxLines, DateTime, DocumentName, ImageDescription, OrientationClass S for separated images SamplesPerPixel = 4
PlanarConfiguration = 1, 2
Compression = 1 (none), 5 (LZW)
PhotometricInterpretation = 5 (Separated)
InkSet = 1 (CMYK)
DotRange, InkNames, DotRange, TargetPrinterClass Y for YCbCr images SamplesPerPixel = 3
BitsPerSample = <8,8,8>
PlanarConfiguration = 1, 2
Compression = 1 (none), 5 (LZW), 7 (JPEG)
PhotometricInterpretation = 6 (YCbCr)
YCbCrCoefficients, YCbCrSubsampling, YCbCrPositioning
(colorimetry info from Appendix H; see above)Class "JPEG" for JPEG images (per TTN2) PhotometricInterpretation = 1 (grayscale), 2 (RGB), 5 (CMYK), 6 (YCbCr)
(Class Y tags if YCbCr)
(Class S tags if CMYK)
Compression = 7 (JPEG)
In addition, the library supports some optional compression algorithms that are, in some cases, of dubious value.
Compression = 32766 NeXT 2-bit encoding Compression = 32809 ThunderScan 4-bit encoding Compression = 32909 Pixar companded 11-bit ZIP encoding Compression = 32946 PKZIP-style Deflate encoding (experimental) Compression = 34676 SGI 32-bit Log Luminance encoding (experimental) Compression = 34677 SGI 24-bit Log Luminance encoding (experimental)Note that there is no support for the JPEG-related tags defined in the 6.0 specification; the JPEG support is based on the post-6.0 proposal given in TIFF Technical Note #2.
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For more information on the experimental Log Luminance encoding consult the materials available at http://positron.cs.berkeley.edu/~gwlarson/pixformat/tiffluv.html . |
The following table shows the tags that are recognized and how they are used by the library. If no use is indicated, then the library reads and writes the tag, but does not use it internally.
| Tag Name | Value | R/W | Library's Use (Comments) |
|---|---|---|---|
| NewSubFileType | 254 | R/W | none (called SubFileType in <tiff.h>) |
| SubFileType | 255 | R/W | none (called OSubFileType in <tiff.h>) |
| ImageWidth | 256 | R/W | lots |
| ImageLength | 257 | R/W | lots |
| BitsPerSample | 258 | R/W | lots |
| Compression | 259 | R/W | to select appropriate codec |
| PhotometricInterpretation | 262 | R/W | lots |
| Thresholding | 263 | R/W | |
| CellWidth | 264 | parsed but ignored | |
| CellLength | 265 | parsed but ignored | |
| FillOrder | 266 | R/W | control bit order |
| DocumentName | 269 | R/W | |
| ImageDescription | 270 | R/W | |
| Make | 271 | R/W | |
| Model | 272 | R/W | |
| StripOffsets | 273 | R/W | data i/o |
| Orientation | 274 | R/W | |
| SamplesPerPixel | 277 | R/W | lots |
| RowsPerStrip | 278 | R/W | data i/o |
| StripByteCounts | 279 | R/W | data i/o |
| MinSampleValue | 280 | R/W | |
| MaxSampleValue | 281 | R/W | |
| XResolution | 282 | R/W | |
| YResolution | 283 | R/W | used by Group 3 2d encoder |
| PlanarConfiguration | 284 | R/W | data i/o |
| PageName | 285 | R/W | |
| XPosition | 286 | R/W | |
| YPosition | 286 | R/W | |
| FreeOffsets | 288 | parsed but ignored | |
| FreeByteCounts | 289 | parsed but ignored | |
| GrayResponseUnit | 290 | parsed but ignored | |
| GrayResponseCurve | 291 | parsed but ignored | |
| Group3Options | 292 | R/W | used by Group 3 codec |
| Group4Options | 293 | R/W | |
| ResolutionUnit | 296 | R/W | used by Group 3 2d encoder |
| PageNumber | 297 | R/W | |
| ColorResponseUnit | 300 | parsed but ignored | |
| TransferFunction | 301 | R/W | |
| Software | 305 | R/W | |
| DateTime | 306 | R/W | |
| Artist | 315 | R/W | |
| HostComputer | 316 | R/W | |
| Predictor | 317 | R/W | used by LZW codec |
| WhitePoint | 318 | R/W | |
| PrimaryChromacities | 319 | R/W | |
| ColorMap | 320 | R/W | |
| TileWidth | 322 | R/W | data i/o |
| TileLength | 323 | R/W | data i/o |
| TileOffsets | 324 | R/W | data i/o |
| TileByteCounts | 324 | R/W | data i/o |
| BadFaxLines | 326 | R/W | |
| CleanFaxData | 327 | R/W | |
| ConsecutiveBadFaxLines | 328 | R/W | |
| SubIFD | 330 | R/W | subimage descriptor support |
| InkSet | 332 | R/W | |
| InkNames | 333 | R/W | |
| DotRange | 336 | R/W | |
| TargetPrinter | 337 | R/W | |
| ExtraSamples | 338 | R/W | lots |
| SampleFormat | 339 | R/W | |
| SMinSampleValue | 340 | R/W | |
| SMaxSampleValue | 341 | R/W | |
| JPEGTables | 347 | R/W | used by JPEG codec |
| YCbCrCoefficients | 529 | R/W | used by TIFFReadRGBAImage support |
| YCbCrSubsampling | 530 | R/W | tile/strip size calculations |
| YCbCrPositioning | 531 | R/W | |
| ReferenceBlackWhite | 532 | R/W | |
| Matteing | 32995 | R | none (obsoleted by ExtraSamples tag) |
| DataType | 32996 | R | none (obsoleted by SampleFormat tag) |
| ImageDepth | 32997 | R/W | tile/strip calculations |
| TileDepth | 32998 | R/W | tile/strip calculations |
| StoNits | 37439 | R/W |
The Matteing and DataType tags have been obsoleted by the 6.0 ExtraSamples and SampleFormat tags. Consult the documentation on the ExtraSamples tag and Associated Alpha for elaboration. Note however that if you use Associated Alpha, you are expected to save data that is pre-multipled by Alpha. If this means nothing to you, check out Porter & Duff's paper in the '84 SIGGRAPH proceedings: "Compositing Digital Images".
The ImageDepth tag is a non-standard, but registered tag that specifies the Z-dimension of volumetric data. The combination of ImageWidth, ImageLength, and ImageDepth, defines a 3D volume of pixels that are further specified by BitsPerSample and SamplesPerPixel. The TileDepth tag (also non-standard, but registered) can be used to specified a subvolume "tiling" of a volume of data.
The Colorimetry, and CMYK tags are additions that appear in TIFF 6.0. Consult the TIFF 6.0 specification included in the doc directory and online.
The JPEG-related tag is specified in TIFF Technical Note #2 which defines a revised JPEG-in-TIFF scheme (revised over that appendix that was part of the TIFF 6.0 specification).