--- /dev/null
+## Copyright (C) 2010 Carnë Draug
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; If not, see <http://www.gnu.org/licenses/>.
+##
+## Based on the documentation at
+## * http://en.wikipedia.org/wiki/Tagged_Image_File_Format
+## * http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
+## * http://ibb.gsf.de/homepage/karsten.rodenacker/IDL/Lsmfile.doc
+## * http://www.awaresystems.be/imaging/tiff/faq.html
+##
+## and the function tiff_read by F. Nedelec, EMBL (www.cytosim.org)
+## * http://www.cytosim.org/misc/index.html
+
+## -*- texinfo -*-
+## @deftypefn {Function File} [@var{value}, @var{offset}] = tiff_tag_read (@var{file}, @var{tag}, @var{ifd})
+## Reads the values of TIFF file tags.
+##
+## @var{file} is a TIFF file and @var{tag} is the tag number to read. If
+## @var{ifd} is given, only the tag value from that IFD (Image File Directory)
+## will be read. By default, reads only the first IFD.
+##
+## @var{value} is the read value from @var{tag}. @var{offset} will be @code{1}
+## if @var{value} is a file offset.
+##
+## @seealso{imread, imfinfo, readexif}
+## @end deftypefn
+
+## * On the TIFF image file header:
+## bytes 00-01 --> byte order used within the file: "II" for little endian
+## and "MM" for big endian byte ordering.
+## bytes 02-03 --> number 42 that identifies the file as TIFF
+## bytes 04-07 --> file offset (in bytes) of the first IFD (Image File Directory)
+##
+## Note: offset is always from the start of the file ("bof" in fread) and first
+## byte has an offset of zero.
+##
+## * On a TIFF's IFD structure:
+## bytes 00-01 --> number of entries (or tags or fields or directories)
+## bytes 02-13 --> the entry (the tag is repeated the number of times
+## specified at the start of the IFD, but always takes
+## 12 bytes of size)
+## bytes XX-XX --> file offset for next IFD (last 4 bytes of the IFD)
+##
+## Note: there must be always one IFD and each IFD must have at least one entry
+##
+## * On an IFD entry (or TIFF's field) structure:
+## bytes 00-01 --> tag that identifies the entry
+## bytes 02-03 --> entry type
+## 1 --> BYTE (uint8)
+## 2 --> ASCII
+## 3 --> SHORT (uint16)
+## 4 --> LONG (uint32)
+## 5 --> RATIONAL (two LONGS)
+## 6 --> SBYTE (int8)
+## 7 --> UNDEFINED (8 bit)
+## 8 --> SSHORT (int16)
+## 9 --> SLONG (int32)
+## 10 --> FLOAT (single IEEE precision)
+## 11 --> DOUBLE (double IEEE precision)
+## bytes 04-07 --> number of values (count)
+## bytes 08-11 --> file offset to the value or value (only if it fits in 4 bytes)
+##
+## Note: file offset of the value may point anywhere in the file, even after the image.
+
+function [value, offset] = tiff_tag_read (file, tag, ifd)
+
+ [FID, msg] = fopen (file, "r", "native");
+ if (msg != 0)
+ error ("Unable to fopen '%s': %s.", file, msg);
+ endif
+
+ # Read byte order
+ byte_order = fread(FID, 2, "char=>char");
+ if ( strcmp(byte_order', "II") )
+ arch = "ieee-le"; # IEEE little endian format
+ elseif ( strcmp(byte_order',"MM") )
+ arch = "ieee-be"; # IEEE big endian format
+ else
+ error("First 2 bytes of header returned '%s'. TIFF file expects either 'II' or 'MM'.", byte_order');
+ endif
+
+ # Read number 42
+ nTIFF = fread(FID, 1, "uint16", arch);
+ if (nTIFF != 42)
+ error("This is not a TIFF file (missing 42 on header at offset 2. Instead got '%g').", tiff_id);
+ endif
+
+ # Read offset and move for the first IFD
+ offset_IFD = fread(FID, 1, "uint32", arch);
+ status = fseek(FID, offset_IFD, "bof");
+ if (status != 0)
+ error("Error on fseek when moving to first IFD.");
+ endif
+
+ # Read number of entries (nTag) and look for the desired tag ID
+ nTag = fread(FID, 1, "uint16", arch);
+ iTag = 0; # Tag index
+ while (1) # Control is made inside the loop
+ iTag++;
+ cTag = fread(FID, 1, "uint16", arch); # Tag ID
+ if (cTag == tag) # Tag ID was found
+ value = read_value (FID, arch, tag); # Read tag value
+ break
+ elseif (iTag == nTag || cTag > tag) # All tags have been read (tags are in ascendent order)
+ error ("Unable to find tag %g.", tag)
+ endif
+ status = fseek(FID, 10, "cof"); # Move to the next tag
+ if (status != 0)
+ error("Error on fseek when moving to tag %g of %g. Last tag read had value of %g", rTag, nTag, tag);
+ endif
+ endwhile
+
+ fclose (FID);
+
+endfunction
+
+#####
+function [value, offset] = read_value (FID, arch, tag)
+
+ tiff_type = fread(FID, 1, "uint16", arch);
+ count = fread(FID, 1, "uint32", arch);
+
+ switch (tiff_type)
+ case 1 # BYTE = 8-bit unsigned integer
+ nBytes = 1;
+ precision = "uint8";
+ case 2 # ASCII = 8-bit byte that contains a 7-bit ASCII code; the last byte must be NUL (binary zero)
+ nBytes = 1;
+ precision = "uchar";
+ case 3 # SHORT = 16-bit (2-byte) unsigned integer
+ nBytes = 2;
+ precision = "uint16";
+ case 4 # LONG = 32-bit (4-byte) unsigned integer
+ nBytes = 4;
+ precision = "uint32";
+ case 5 # RATIONAL = Two LONGs: the first represents the numerator of a fraction; the second, the denominator
+ nBytes = 8;
+ precision = "uint32";
+ case 6 # SBYTE = An 8-bit signed (twos-complement) integer
+ nBytes = 1;
+ precision = "int8";
+ case 7 # UNDEFINED = An 8-bit byte that may contain anything, depending on the definition of the field
+ nBytes = 1;
+ precision = "uchar";
+ case 8 # SSHORT = A 16-bit (2-byte) signed (twos-complement) integer
+ nBytes = 2;
+ precision = "int16";
+ case 9 # SLONG = A 32-bit (4-byte) signed (twos-complement) integer
+ nBytes = 4;
+ precision = "int32";
+ case 10 # SRATIONAL = Two SLONG’s: the first represents the numerator of a fraction, the second the denominator
+ nBytes = 8;
+ precision = "int32";
+ case 11 # FLOAT = Single precision (4-byte) IEEE format
+ nBytes = 4;
+ precision = "float32";
+ case 12 # DOUBLE = Double precision (8-byte) IEEE format
+ nBytes = 8;
+ precision = "float64";
+ otherwise # Warning (from TIFF file specifications): It is possible that other TIFF field types will be added in the future
+ error("TIFF type %i not supported", tiff_type)
+ endswitch
+
+ if ( (nBytes*count) > 4 ) # If it doesn't fit in 4 bytes, it's an offset
+ offset = 1;
+ value = fread(FID, 1, "uint32", arch);
+ ## The file offset must be an even number
+ if ( rem(value,2) != 0 )
+ error("Couldn't find correct value offset for tag %g", tag);
+ endif
+ else
+ offset = 0;
+ ## read here
+ switch precision
+ case { 5, 10 }
+ value = fread(FID, 2*count, precision, arch);
+ otherwise
+ value = fread(FID, count, precision, arch);
+ endswitch
+ if (precision == 2)
+ value = char(value');
+ endif
+ endif
+
+endfunction
git://git.creatis.insa-lyon.fr / CreaPhase.git / blobdiff