Добавление пользовательских тегов в файл TIFF

Следуя указаниям доброго джентльмена по имени Пол Хекберт из списка рассылки пользователей TIFF, вот код, который наконец-то сработал для меня. Было два ключа к нему:

(1) Правильное определение полей TIFFFieldInfo способом, отличным от примера, приведенного в документации.
(2) Использование шаблона «extender» для инкапсуляции вызова TIFFMergeFieldInfo, но при этом до открываем файл. Если я оставляю вызов до открытия файла, то при чтении файла с пользовательскими тегами сразу после открытия файла будет выдано несколько сообщений «Предупреждение, неизвестное поле».

Вот код:

#include "stdafx.h"#include "PGM.h"#include "tiffio.h"
// There are a number of TIFF-related definitions we need to make in order to support the custom tags
// that we want to include in our files. The form of these definitions and subroutines comes straight
// out of the libtiff documentation, and the values of the custom tags themselves come from the
// range (65000-75535) defined in the TIFF specification as "reusable" and suitable for private use
// within organisations. See http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
#define N(a) (sizeof(a) / sizeof (a[0]))
#define TIFFTAG_INCIDENTPOWER     65000
#define TIFFTAG_REFLECTEDPOWER    65001
#define TIFFTAG_T1                65002
#define TIFFTAG_T2                65003
#define TIFFTAG_HUMIDITY          65004
#define TIFFTAG_EXPOSURE          65005

static const TIFFFieldInfo xtiffFieldInfo[] = {
{ TIFFTAG_INCIDENTPOWER,  1, 1, TIFF_LONG,  FIELD_CUSTOM, 0, 0, const_cast<char*>("LaserIncidentPower") },
{ TIFFTAG_REFLECTEDPOWER, 1, 1, TIFF_LONG,  FIELD_CUSTOM, 0, 0, const_cast<char*>("LaserReflectedPower") },
{ TIFFTAG_T1,             1, 1, TIFF_FLOAT, FIELD_CUSTOM, 0, 0, const_cast<char*>("Temperature_1") },
{ TIFFTAG_T2,             1, 1, TIFF_FLOAT, FIELD_CUSTOM, 0, 0, const_cast<char*>("Temperature_2") },
{ TIFFTAG_HUMIDITY,       1, 1, TIFF_FLOAT, FIELD_CUSTOM, 0, 0, const_cast<char*>("Humidity") },
{ TIFFTAG_EXPOSURE,       1, 1, TIFF_FLOAT, FIELD_CUSTOM, 0, 0, const_cast<char*>("ExposureTime(ms)") }
};                                                                    // The casts are necessary because the
// string literals are inherently const,
// but the definition of TIFFFieldInfo
// requires a non-const string pointer.
// The Intel and Microsoft compilers
// tolerate this, but gcc doesn't.

static TIFFExtendProc parent_extender = NULL;  // In case we want a chain of extensions

static void registerCustomTIFFTags(TIFF *tif)
{
/* Install the extended Tag field info */
int error = TIFFMergeFieldInfo(tif, xtiffFieldInfo, N(xtiffFieldInfo));

if (parent_extender)
(*parent_extender)(tif);
}

static void augment_libtiff_with_custom_tags() {
static bool first_time = true;
if (!first_time) return;
first_time = false;
parent_extender = TIFFSetTagExtender(registerCustomTIFFTags);
}

void saveAsTiff(int nx, int ny, unsigned short *image, const char* filename,
int Power1, int Power2, float T1, float T2, float Humidity, float Exposure)
{
// Create the TIFF directory object:
augment_libtiff_with_custom_tags();
TIFF* tif = TIFFOpen(filename, "w");

// Set the tags: first the standard ones...
TIFFSetField(tif, TIFFTAG_IMAGEWIDTH, nx);
TIFFSetField(tif, TIFFTAG_IMAGELENGTH, ny);
TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 16);
TIFFSetField(tif, TIFFTAG_COMPRESSION, COMPRESSION_DEFLATE);
TIFFSetField(tif, TIFFTAG_ZIPQUALITY, 6); // Takes maximum advantage of Intel ZLIB enhancements
TIFFSetField(tif, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_MINISBLACK);
TIFFSetField(tif, TIFFTAG_ORIENTATION, static_cast<int>(ORIENTATION_TOPLEFT));
TIFFSetField(tif, TIFFTAG_SAMPLESPERPIXEL, 1);
TIFFSetField(tif, TIFFTAG_ROWSPERSTRIP, ny);
// Saving the whole image in a single block makes heavy
// demands on memory but should enable optimum compression
TIFFSetField(tif, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG);

// ... and now our own custom ones:
TIFFSetField(tif, TIFFTAG_INCIDENTPOWER, Power1);
TIFFSetField(tif, TIFFTAG_REFLECTEDPOWER, Power2);
TIFFSetField(tif, TIFFTAG_T1, T1);
TIFFSetField(tif, TIFFTAG_T2, T2);
TIFFSetField(tif, TIFFTAG_HUMIDITY, Humidity);
TIFFSetField(tif, TIFFTAG_EXPOSURE, Exposure);

TIFFWriteEncodedStrip(tif, 0, static_cast<void *>(image), nx * ny * 2);
// The '* 2' is present because each pixel
// has 16 bits, hence two bytes
// Write the directory to a file, and close it:
TIFFWriteDirectory(tif);
TIFFClose(tif);
}

void readFromTiff(int *nx, int *ny, unsigned short **image, const char* filename,
int *Power1, int *Power2, float *T1, float *T2, float *Humidity, float *Exposure)
{
// Create the TIFF directory object:
augment_libtiff_with_custom_tags();
TIFF* tif = TIFFOpen(filename, "r");
if (NULL == tif)
{
*nx = -1;
*ny = -1;
return;
}

// Read in the image size and metadata:
TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, nx);
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, ny);
TIFFGetField(tif, TIFFTAG_INCIDENTPOWER, Power1);
TIFFGetField(tif, TIFFTAG_REFLECTEDPOWER, Power2);
TIFFGetField(tif, TIFFTAG_T1, T1);
TIFFGetField(tif, TIFFTAG_T2, T2);
TIFFGetField(tif, TIFFTAG_HUMIDITY, Humidity);
TIFFGetField(tif, TIFFTAG_EXPOSURE, Exposure);

// Dimension the buffer, and read in the image data itself:
*image = new unsigned short[(*nx) * (*ny)];
TIFFReadEncodedStrip(tif, static_cast<tstrip_t>(0), static_cast<void *>(*image), static_cast<tsize_t>(-1));
TIFFClose(tif);
}

int _tmain(int argc, _TCHAR* argv[])
{
// Variables to hold the image
int nx, ny;
unsigned short *image = nullptr;

// Information we'd like to put into our custom tags:
int Power1 = 1000000;
int Power2 = 8;
float T1 = 23.5f;
float T2 = -18.7f;
float Humidity = 0.98f;
float Exposure = 0.001f;

// Read the test image in from a PGM file:
readFromPGM(&nx, &ny, &image, "TestImage.pgm");

// Save the image as a TIF file:
saveAsTiff(nx, ny, image, "TestImage.tif", Power1, Power2, T1, T2, Humidity, Exposure);

// Prepare to read back in: first clear the various fields
Power1 = 0;
Power2 = 0;
T1 = 0.0f;
T2 = 0.0f;
Humidity = 0.0f;
Exposure = 0.0f;
nx = 0;
ny = 0;
delete [] image;

readFromTiff(&nx, &ny, &image, "TestImage.tif", &Power1, &Power2, &T1, &T2, &Humidity, &Exposure);

printf("Image size = %d, %d\r\n", ny, ny);
printf("Power1 = %d\r\n", Power1);
printf("Power2 = %d\r\n", Power2);
printf("T1 = %6.3f\r\n", T1);
printf("T2 = %6.3f\r\n", T2);
printf("Humidity = %6.3f\r\n", Humidity);
printf("Exposure = %6.3f\r\n", Exposure);
return 0;
}