Pure python tiff tools to handle all tags and IFDs.
Project description
Pure Python tools for reading and writing all TIFF IFDs, sub-IFDs, and tags.
Developed by Kitware, Inc. with funding from The National Cancer Institute.
Example
import tifftools
info = tifftools.read_tiff('photograph.tif')
info['ifds'][0]['tags'][tifftools.Tag.ImageDescription.value] = {
'data': 'A dog digging.',
'datatype': tifftools.Datatype.ASCII
}
exififd = info['ifds'][0]['tags'][tifftools.Tag.EXIFIFD.value]['ifds'][0]
exififd['tags'][tifftools.constants.EXIFTag.FNumber.value] = {
'data': [54, 10],
'datatype': tifftools.Datatype.RATIONAL
}
tifftools.write_tiff(info, 'photograph_tagged.tif')Purpose
tifftools provides a library and a command line program for maniplulating TIFF files. It can split multiple images apart, merge images together, set any tag in any IFD, and dump all IFDs and tags in a single command. It only uses python standard library modules, and is therefore widely compatible.
Rationale
There was a need to combine images from multiple TIFF files without altering the image data or losing any tag information. Further, when changing tag values, it was essential that the old values were fully removed from the output.
The command line tools associated with libtiff are commonly used for similar purposes. The libtiff command tools have significant limitations: tiffdump and tiffinfo require multiple commands to see information from all IFDs. tiffset does not remove data from a file; rather it appends to the file to only reference new data, leaving the old values inside the file. tiffsplit doesn’t keep tags it doesn’t recognize, loosing data. tiffcp always reencodes images and will fail for compression types it does not know.
Likewise, there is a wide variety of EXIF tools. For the most part, these only alter tags, usually by appending to the existing file.
Many programs deal with both classic and BigTIFF. Some will start writing a classic TIFF, but leave a small amount of unused space just after the file header. If the file exceeds 4Gb, parts of the file are rewritten to convert it to a BigTIFF file, leaving small amounts of abandoned data within the file.
tifftools fills this need. All tags are copied, even if unknown. Files are always rewritten so that there is never abandoned data inside the file. tifftools dump shows information on all IFDs and tags. Many of the command line options are directly inspired from libtiff.
tifftools does NOT compress or decompress any image data. This is not an image viewer. If you need to recompress an image or otherwise manipulate pixel data, use libtiff or another library.
Commands
tiff_split
tiff_concat
tiff_dump
tiff_set
Library Functions
read_tiff
write_tiff
Constants
Tag
Datatype
get_or_create_tag
EXIFTag, GPSTag, etc.
TIFF File Structure
TIFF Files consist of one or more IFDs (Image File Directories). These can be located anywhere within the file, and are referenced by their absolute position within the file. IFDs can refer to image data but they can also contain a collection of metadata (for instance, EXIF or GPS data). Small data values are stored directly in the IFD. Bigger data values (such as image data, longer string, or lists of numbers) are referenced by the IFD and are stored elsewhere in the file.
In the simple case, a TIFF file may have a list of IFDs, each one referencing the next. However, a complex TIFF file, such as those used by some Whole-Slide Image (WSI) microscopy systems, can have IFDs organized in a branching structure, where some IFDs are in a list and some reference SubIFDs with additional images.
TIFF files can have their primary data stored in either little-endian or big-endian. Offsets to data are store as absolute numbers inside a TIFF file. There are two variations: “classic” and “BigTIFF” which use 32-bits and 64-bits for these offsets, respectively. If the file size exceeds 4 Gb or uses 64-bit integer datatypes, it must be written as a BigTIFF.
Limitations
Unknown tags that are offsets and have a datatype other than IFD or IFD8 won’t be copied properly, as it is impossible to distinguish integer data from offsets given LONG or LONG8 datatypes. This can be remedied by defining a new TiffConstant record which contains a bytecounts entry to instruct whether the offsets refer to fixed length data or should get the length of data from another tag.
Because files are ALWAYS rewritten, tifftools is slower than libtiff’s tiffset and most EXIF tools.
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