示例#1
0
BOOL DLL_CALLCONV 
FreeImage_SetTagValue(FITAG *tag, const void *value) {
	if(tag) {
		FITAGHEADER *tag_header = (FITAGHEADER *)tag->data;
		// first, check the tag
		if(tag_header->count * FreeImage_TagDataWidth(tag_header->type) != tag_header->length) {
			// invalid data count ?
			return FALSE;
		}

		if(tag_header->value) free(tag_header->value);

		switch(tag_header->type) {
			case FIDT_ASCII:
			{
				tag_header->value = (char*)malloc((tag_header->length + 1) * sizeof(char));
				char *src_data = (char*)value;
				char *dst_data = (char*)tag_header->value;
				for(DWORD i = 0; i < tag_header->length; i++) {
					dst_data[i] = src_data[i];
				}
				dst_data[tag_header->length] = '\0';
			}
			break;

			default:
				tag_header->value = malloc(tag_header->length * sizeof(BYTE));
				memcpy(tag_header->value, value, tag_header->length);
				break;
		}
		return TRUE;
	}
	return FALSE;
}
示例#2
0
BOOL DLL_CALLCONV 
FreeImage_SetMetadata(FREE_IMAGE_MDMODEL model, FIBITMAP *dib, const char *key, FITAG *tag) {
	if(!dib) 
		return FALSE;

	TAGMAP *tagmap = NULL;

	// get the metadata model
	METADATAMAP *metadata = ((FREEIMAGEHEADER *)dib->data)->metadata;
	tagmap = (*metadata)[model];

	if(key != NULL) {

		if(!tagmap) {
			// this model, doesn't exist: create it 
			tagmap = new TAGMAP();
			(*metadata)[model] = tagmap;
		}

		// first check the tag
		if(tag) {
			if(FreeImage_GetTagKey(tag) == NULL) {
				FreeImage_SetTagKey(tag, key);
			} else if(strcmp(key, FreeImage_GetTagKey(tag)) != 0) {
				// set the tag key
				FreeImage_SetTagKey(tag, key);
			}
			if(FreeImage_GetTagCount(tag) * FreeImage_TagDataWidth(FreeImage_GetTagType(tag)) != FreeImage_GetTagLength(tag)) {
				// invalid data count ?
				return FALSE;
			}
		}

		// delete existing tag
		FITAG *old_tag = (*tagmap)[key];
		if(old_tag) {
			FreeImage_DeleteTag(old_tag);
		}

		// create a new tag
		(*tagmap)[key] = FreeImage_CloneTag(tag);
	}
	else {
		// destroy the metadata model
		if(tagmap) {
			for(TAGMAP::iterator i = tagmap->begin(); i != tagmap->end(); i++) {
				FITAG *tag = (*i).second;
				FreeImage_DeleteTag(tag);
			}

			delete tagmap;
			(*metadata)[model] = NULL;
		}
	}

	return TRUE;
}
示例#3
0
/**
Write all known exif tags

@param tif TIFF handle
@param md_model Metadata model from where to load the tags
@param dib Image being written
@return Returns TRUE if successful, returns FALSE otherwise
*/
BOOL 
tiff_write_exif_tags(TIFF *tif, TagLib::MDMODEL md_model, FIBITMAP *dib) {
	char defaultKey[16];
	
	// only EXIF_MAIN so far
	if(md_model != TagLib::EXIF_MAIN) {
		return FALSE;
	}
	
	if(FreeImage_GetMetadataCount(FIMD_EXIF_MAIN, dib) == 0) {
		return FALSE;
	}
	
	TagLib& tag_lib = TagLib::instance();
	
	for (int fi = 0, nfi = (int)tif->tif_nfields; nfi > 0; nfi--, fi++) {
		const TIFFField *fld = tif->tif_fields[fi];
		
		const uint32 tag_id = TIFFFieldTag(fld);

		if(skip_write_field(tif, tag_id)) {
			// skip tags that are already handled by the LibTIFF writing process
			continue;
		}

		FITAG *tag = NULL;
		// get the tag key
		const char *key = tag_lib.getTagFieldName(TagLib::EXIF_MAIN, (WORD)tag_id, defaultKey);

		if(FreeImage_GetMetadata(FIMD_EXIF_MAIN, dib, key, &tag)) {
			FREE_IMAGE_MDTYPE tag_type = FreeImage_GetTagType(tag);
			TIFFDataType tif_tag_type = TIFFFieldDataType(fld);
			
			// check for identical formats

			// (enum value are the sames between FREE_IMAGE_MDTYPE and TIFFDataType types)
			if((int)tif_tag_type != (int)tag_type) {
				// skip tag or _TIFFmemcpy will fail
				continue;
			}
			// type of storage may differ (e.g. rationnal array vs float array type)
			if((unsigned)_TIFFDataSize(tif_tag_type) != FreeImage_TagDataWidth(tag_type)) {
				// skip tag or _TIFFmemcpy will fail
				continue;
			}

			if(tag_type == FIDT_ASCII) {
				TIFFSetField(tif, tag_id, FreeImage_GetTagValue(tag));
			} else {
				TIFFSetField(tif, tag_id, FreeImage_GetTagCount(tag), FreeImage_GetTagValue(tag));
			}
		}
	}

	return TRUE;
}
示例#4
0
void
tiff_read_geotiff_profile(TIFF *tif, FIBITMAP *dib) {
	char defaultKey[16];

	size_t tag_size = sizeof(xtiffFieldInfo) / sizeof(xtiffFieldInfo[0]);

	TagLib& tag_lib = TagLib::instance();

	for(unsigned i = 0; i < tag_size; i++) {

		const TIFFFieldInfo *fieldInfo = &xtiffFieldInfo[i];

		if(fieldInfo->field_type == TIFF_ASCII) {
			char *params = NULL;

			if(TIFFGetField(tif, fieldInfo->field_tag, &params)) {
				// create a tag
				FITAG *tag = FreeImage_CreateTag();
				if(!tag)
					return;

				WORD tag_id = (WORD)fieldInfo->field_tag;

				FreeImage_SetTagType(tag, (FREE_IMAGE_MDTYPE)fieldInfo->field_type);
				FreeImage_SetTagID(tag, tag_id);
				FreeImage_SetTagKey(tag, tag_lib.getTagFieldName(TagLib::GEOTIFF, tag_id, defaultKey));
				FreeImage_SetTagDescription(tag, tag_lib.getTagDescription(TagLib::GEOTIFF, tag_id));
				FreeImage_SetTagLength(tag, (DWORD)strlen(params) + 1);
				FreeImage_SetTagCount(tag, FreeImage_GetTagLength(tag));
				FreeImage_SetTagValue(tag, params);
				FreeImage_SetMetadata(FIMD_GEOTIFF, dib, FreeImage_GetTagKey(tag), tag);

				// delete the tag
				FreeImage_DeleteTag(tag);
			}
		} else {
			short tag_count = 0;
			void* data = NULL;

			if(TIFFGetField(tif, fieldInfo->field_tag, &tag_count, &data)) {
				// create a tag
				FITAG *tag = FreeImage_CreateTag();
				if(!tag)
					return;

				WORD tag_id = (WORD)fieldInfo->field_tag;
				FREE_IMAGE_MDTYPE tag_type = (FREE_IMAGE_MDTYPE)fieldInfo->field_type;

				FreeImage_SetTagType(tag, tag_type);
				FreeImage_SetTagID(tag, tag_id);
				FreeImage_SetTagKey(tag, tag_lib.getTagFieldName(TagLib::GEOTIFF, tag_id, defaultKey));
				FreeImage_SetTagDescription(tag, tag_lib.getTagDescription(TagLib::GEOTIFF, tag_id));
				FreeImage_SetTagLength(tag, FreeImage_TagDataWidth(tag_type) * tag_count);
				FreeImage_SetTagCount(tag, tag_count);
				FreeImage_SetTagValue(tag, data);
				FreeImage_SetMetadata(FIMD_GEOTIFF, dib, FreeImage_GetTagKey(tag), tag);

				// delete the tag
				FreeImage_DeleteTag(tag);
			}
		}
	} // for(tag_size)
}
示例#5
0
/**
	Process Exif directory

	@param dib Input FIBITMAP
	@param tiffp Pointer to the TIFF header
	@param offset 0th IFD offset
	@param length Length of the datafile
	@param msb_order Endianess order of the datafile
	@return 
*/
static BOOL 
jpeg_read_exif_dir(FIBITMAP *dib, const BYTE *tiffp, unsigned long offset, unsigned int length, BOOL msb_order) {
	WORD de, nde;

	std::stack<WORD>			destack;	// directory entries stack
	std::stack<BYTE*>			ifdstack;	// IFD stack
	std::stack<TagLib::MDMODEL>	modelstack; // metadata model stack

	// Keep a list of already visited IFD to avoid stack overflows 
	// when recursive/cyclic directory structures exist. 
	// This kind of recursive Exif file was encountered with Kodak images coming from 
	// KODAK PROFESSIONAL DCS Photo Desk JPEG Export v3.2 W
	std::map<DWORD, int> visitedIFD;

    #define DIR_ENTRY_ADDR(_start, _entry) (_start + 2 + (12 * _entry))

	// set the metadata model to Exif

	TagLib::MDMODEL md_model = TagLib::EXIF_MAIN;

	// set the pointer to the first IFD and follow it were it leads.

	BYTE *ifdp = (BYTE*)tiffp + offset;

	de = 0;

	do {
		// if there is anything on the stack then pop it off
		if(!destack.empty()) {
			ifdp		= ifdstack.top();	ifdstack.pop();
			de			= destack.top();	destack.pop();
			md_model	= modelstack.top();	modelstack.pop();
		}

		// remember that we've visited this directory so that we don't visit it again later
		DWORD visited = (DWORD)( (((size_t)ifdp & 0xFFFF) << 16) | (size_t)de );
		if(visitedIFD.find(visited) != visitedIFD.end()) {
			continue;
		} else {
			visitedIFD[visited] = 1;	// processed
		}

		// determine how many entries there are in the current IFD
		nde = ReadUint16(msb_order, ifdp);

		for(; de < nde; de++) {
			char *pde = NULL;	// pointer to the directory entry
			char *pval = NULL;	// pointer to the tag value
			
			// create a tag
			FITAG *tag = FreeImage_CreateTag();
			if(!tag) return FALSE;

			// point to the directory entry
			pde = (char*) DIR_ENTRY_ADDR(ifdp, de);

			// get the tag ID
			FreeImage_SetTagID(tag, ReadUint16(msb_order, pde));
			// get the tag format
			WORD tag_type = (WORD)ReadUint16(msb_order, pde + 2);
            if((tag_type - 1) >= EXIF_NUM_FORMATS) {
                // a problem occured : delete the tag (not free'd after)
			    FreeImage_DeleteTag(tag);
				// break out of the for loop
				break;
            }
			FreeImage_SetTagType(tag, (FREE_IMAGE_MDTYPE)tag_type);

			// get number of components
			FreeImage_SetTagCount(tag, ReadUint32(msb_order, pde + 4));
			// get the size of the tag value in bytes
			FreeImage_SetTagLength(tag, FreeImage_GetTagCount(tag) * FreeImage_TagDataWidth((WORD)FreeImage_GetTagType(tag)));

			if(FreeImage_GetTagLength(tag) <= 4) {
				// 4 bytes or less and value is in the dir entry itself
				pval = pde + 8;
			} else {
				// if its bigger than 4 bytes, the directory entry contains an offset
				// first check if offset exceeds buffer, at this stage FreeImage_GetTagLength may return invalid data
				DWORD offset_value = ReadUint32(msb_order, pde + 8);
				if(offset_value > length) {
					// a problem occured : delete the tag (not free'd after)
					FreeImage_DeleteTag(tag);
					// jump to next entry
					continue;
				}
				// now check if offset + tag length exceeds buffer
				if(offset_value > length - FreeImage_GetTagLength(tag)) {
					// a problem occured : delete the tag (not free'd after)
					FreeImage_DeleteTag(tag);
					// jump to next entry
					continue;
				}
				pval = (char*)(tiffp + offset_value);
			}

			// check for a IFD offset
			BOOL isIFDOffset = FALSE;
			switch(FreeImage_GetTagID(tag)) {
				case TAG_EXIF_OFFSET:
				case TAG_GPS_OFFSET:
				case TAG_INTEROP_OFFSET:
				case TAG_MAKER_NOTE:
					isIFDOffset = TRUE;
					break;
			}
			if(isIFDOffset)	{
				DWORD sub_offset = 0;
				TagLib::MDMODEL next_mdmodel = md_model;
				BYTE *next_ifd = ifdp;
				
				// get offset and metadata model
				if (FreeImage_GetTagID(tag) == TAG_MAKER_NOTE) {
					processMakerNote(dib, pval, msb_order, &sub_offset, &next_mdmodel);
					next_ifd = (BYTE*)pval + sub_offset;
				} else {
					processIFDOffset(tag, pval, msb_order, &sub_offset, &next_mdmodel);
					next_ifd = (BYTE*)tiffp + sub_offset;
				}

				if((sub_offset < (DWORD) length) && (next_mdmodel != TagLib::UNKNOWN)) {
					// push our current directory state onto the stack
					ifdstack.push(ifdp);
					// bump to the next entry
					de++;
					destack.push(de);

					// push our current metadata model
					modelstack.push(md_model);

					// push new state onto of stack to cause a jump
					ifdstack.push(next_ifd);
					destack.push(0);

					// select a new metadata model
					modelstack.push(next_mdmodel);
					
					// delete the tag as it won't be stored nor deleted in the for() loop
					FreeImage_DeleteTag(tag);
					
					break; // break out of the for loop
				}
				else {
					// unsupported camera model, canon maker tag or or something unknown
					// process as a standard tag
					processExifTag(dib, tag, pval, msb_order, md_model);
				}			

			} else {
				// process as a standard tag
				processExifTag(dib, tag, pval, msb_order, md_model);
			}
			
			// delete the tag
			FreeImage_DeleteTag(tag);

        } // for(nde)

		// additional thumbnail data is skipped

    } while (!destack.empty()); 


	return TRUE;
}
示例#6
0
BOOL DLL_CALLCONV 
FreeImage_SetMetadata(FREE_IMAGE_MDMODEL model, FIBITMAP *dib, const char *key, FITAG *tag) {
	if(!dib) 
		return FALSE;

	TAGMAP *tagmap = NULL;

	// get the metadata model
	METADATAMAP *metadata = ((FREEIMAGEHEADER *)dib->data)->metadata;
	METADATAMAP::iterator model_iterator = metadata->find(model);
	if (model_iterator != metadata->end()) {
		tagmap = model_iterator->second;
	}

	if(key != NULL) {

		if(!tagmap) {
			// this model, doesn't exist: create it 
			tagmap = new(std::nothrow) TAGMAP();
			(*metadata)[model] = tagmap;
		}
		
		if(tag) {
			// first check the tag
			if(FreeImage_GetTagKey(tag) == NULL) {
				FreeImage_SetTagKey(tag, key);
			} else if(strcmp(key, FreeImage_GetTagKey(tag)) != 0) {
				// set the tag key
				FreeImage_SetTagKey(tag, key);
			}
			if(FreeImage_GetTagCount(tag) * FreeImage_TagDataWidth(FreeImage_GetTagType(tag)) != FreeImage_GetTagLength(tag)) {
				FreeImage_OutputMessageProc(FIF_UNKNOWN, "Invalid data count for tag '%s'", key);
				return FALSE;
			}

			// fill the tag ID if possible and if it's needed
			TagLib& tag_lib = TagLib::instance();
			switch(model) {
				case FIMD_IPTC:
				{
					int id = tag_lib.getTagID(TagLib::IPTC, key);
					/*
					if(id == -1) {
						FreeImage_OutputMessageProc(FIF_UNKNOWN, "IPTC: Invalid key '%s'", key);
					}
					*/
					FreeImage_SetTagID(tag, (WORD)id);
				}
				break;

				default:
					break;
			}

			// delete existing tag
			FITAG *old_tag = (*tagmap)[key];
			if(old_tag) {
				FreeImage_DeleteTag(old_tag);
			}

			// create a new tag
			(*tagmap)[key] = FreeImage_CloneTag(tag);
		}
		else {
			// delete existing tag
			TAGMAP::iterator i = tagmap->find(key);
			if(i != tagmap->end()) {
				FITAG *old_tag = (*i).second;
				FreeImage_DeleteTag(old_tag);
				tagmap->erase(key);
			}
		}
	}
	else {
		// destroy the metadata model
		if(tagmap) {
			for(TAGMAP::iterator i = tagmap->begin(); i != tagmap->end(); i++) {
				FITAG *tag = (*i).second;
				FreeImage_DeleteTag(tag);
			}

			delete tagmap;
			metadata->erase(model_iterator);
		}
	}

	return TRUE;
}
示例#7
0
/**
	Process Exif directory

	@param dib Input FIBITMAP
	@param tiffp Pointer to the TIFF header
	@param offset 0th IFD offset
	@param length Length of the datafile
	@param msb_order Endianess order of the datafile
	@return
*/
static BOOL
jpeg_read_exif_dir(FIBITMAP *dib, const BYTE *tiffp, unsigned long offset, unsigned int length, BOOL msb_order) {
    WORD de, nde;

    std::stack<WORD>			destack;	// directory entries stack
    std::stack<const BYTE*>		ifdstack;	// IFD stack
    std::stack<TagLib::MDMODEL>	modelstack; // metadata model stack

    // Keep a list of already visited IFD to avoid stack overflows
    // when recursive/cyclic directory structures exist.
    // This kind of recursive Exif file was encountered with Kodak images coming from
    // KODAK PROFESSIONAL DCS Photo Desk JPEG Export v3.2 W
    std::map<DWORD, int> visitedIFD;

    /*
    "An Image File Directory (IFD) consists of a 2-byte count of the number of directory
    entries (i.e. the number of fields), followed by a sequence of 12-byte field
    entries, followed by a 4-byte offset of the next IFD (or 0 if none)."
    The "next IFD" (1st IFD) is the thumbnail.
    */
#define DIR_ENTRY_ADDR(_start, _entry) (_start + 2 + (12 * _entry))

    // set the metadata model to Exif

    TagLib::MDMODEL md_model = TagLib::EXIF_MAIN;

    // set the pointer to the first IFD (0th IFD) and follow it were it leads.

    const BYTE *ifd0th = (BYTE*)tiffp + offset;

    const BYTE *ifdp = ifd0th;

    de = 0;

    do {
        // if there is anything on the stack then pop it off
        if(!destack.empty()) {
            ifdp		= ifdstack.top();
            ifdstack.pop();
            de			= destack.top();
            destack.pop();
            md_model	= modelstack.top();
            modelstack.pop();
        }

        // remember that we've visited this directory and entry so that we don't visit it again later
        DWORD visited = (DWORD)( (((size_t)ifdp & 0xFFFF) << 16) | (size_t)de );
        if(visitedIFD.find(visited) != visitedIFD.end()) {
            continue;
        } else {
            visitedIFD[visited] = 1;	// processed
        }

        // determine how many entries there are in the current IFD
        nde = ReadUint16(msb_order, ifdp);

        for(; de < nde; de++) {
            char *pde = NULL;	// pointer to the directory entry
            char *pval = NULL;	// pointer to the tag value

            // create a tag
            FITAG *tag = FreeImage_CreateTag();
            if(!tag) return FALSE;

            // point to the directory entry
            pde = (char*) DIR_ENTRY_ADDR(ifdp, de);

            // get the tag ID
            FreeImage_SetTagID(tag, ReadUint16(msb_order, pde));
            // get the tag type
            WORD tag_type = (WORD)ReadUint16(msb_order, pde + 2);
            if((tag_type - 1) >= EXIF_NUM_FORMATS) {
                // a problem occured : delete the tag (not free'd after)
                FreeImage_DeleteTag(tag);
                // break out of the for loop
                break;
            }
            FreeImage_SetTagType(tag, (FREE_IMAGE_MDTYPE)tag_type);

            // get number of components
            FreeImage_SetTagCount(tag, ReadUint32(msb_order, pde + 4));
            // check that tag length (size of the tag value in bytes) will fit in a DWORD
            unsigned tag_data_width = FreeImage_TagDataWidth(FreeImage_GetTagType(tag));
            if (tag_data_width != 0 && FreeImage_GetTagCount(tag) > ~(DWORD)0 / tag_data_width) {
                FreeImage_DeleteTag(tag);
                // jump to next entry
                continue;
            }
            FreeImage_SetTagLength(tag, FreeImage_GetTagCount(tag) * tag_data_width);

            if(FreeImage_GetTagLength(tag) <= 4) {
                // 4 bytes or less and value is in the dir entry itself
                pval = pde + 8;
            } else {
                // if its bigger than 4 bytes, the directory entry contains an offset
                // first check if offset exceeds buffer, at this stage FreeImage_GetTagLength may return invalid data
                DWORD offset_value = ReadUint32(msb_order, pde + 8);
                if(offset_value > length) {
                    // a problem occured : delete the tag (not free'd after)
                    FreeImage_DeleteTag(tag);
                    // jump to next entry
                    continue;
                }
                // now check that length does not exceed the buffer size
                if(FreeImage_GetTagLength(tag) > length - offset_value) {
                    // a problem occured : delete the tag (not free'd after)
                    FreeImage_DeleteTag(tag);
                    // jump to next entry
                    continue;
                }
                pval = (char*)(tiffp + offset_value);
            }

            // check for a IFD offset
            BOOL isIFDOffset = FALSE;
            switch(FreeImage_GetTagID(tag)) {
            case TAG_EXIF_OFFSET:
            case TAG_GPS_OFFSET:
            case TAG_INTEROP_OFFSET:
            case TAG_MAKER_NOTE:
                isIFDOffset = TRUE;
                break;
            }
            if(isIFDOffset)	{
                DWORD sub_offset = 0;
                TagLib::MDMODEL next_mdmodel = md_model;
                const BYTE *next_ifd = ifdp;

                // get offset and metadata model
                if (FreeImage_GetTagID(tag) == TAG_MAKER_NOTE) {
                    processMakerNote(dib, pval, msb_order, &sub_offset, &next_mdmodel);
                    next_ifd = (BYTE*)pval + sub_offset;
                } else {
                    processIFDOffset(tag, pval, msb_order, &sub_offset, &next_mdmodel);
                    next_ifd = (BYTE*)tiffp + sub_offset;
                }

                if((sub_offset < (DWORD) length) && (next_mdmodel != TagLib::UNKNOWN)) {
                    // push our current directory state onto the stack
                    ifdstack.push(ifdp);
                    // bump to the next entry
                    de++;
                    destack.push(de);

                    // push our current metadata model
                    modelstack.push(md_model);

                    // push new state onto of stack to cause a jump
                    ifdstack.push(next_ifd);
                    destack.push(0);

                    // select a new metadata model
                    modelstack.push(next_mdmodel);

                    // delete the tag as it won't be stored nor deleted in the for() loop
                    FreeImage_DeleteTag(tag);

                    break; // break out of the for loop
                }
                else {
                    // unsupported camera model, canon maker tag or something unknown
                    // process as a standard tag
                    processExifTag(dib, tag, pval, msb_order, md_model);
                }

            } else {
                // process as a standard tag
                processExifTag(dib, tag, pval, msb_order, md_model);
            }

            // delete the tag
            FreeImage_DeleteTag(tag);

        } // for(nde)

        // additional thumbnail data is skipped

    } while (!destack.empty());

    //
    // --- handle thumbnail data ---
    //

    const WORD entriesCount0th = ReadUint16(msb_order, ifd0th);

    DWORD next_offset = ReadUint32(msb_order, DIR_ENTRY_ADDR(ifd0th, entriesCount0th));
    if((next_offset == 0) || (next_offset >= length)) {
        return TRUE; //< no thumbnail
    }

    const BYTE* const ifd1st = (BYTE*)tiffp + next_offset;
    const WORD entriesCount1st = ReadUint16(msb_order, ifd1st);

    unsigned thCompression = 0;
    unsigned thOffset = 0;
    unsigned thSize = 0;

    for(int e = 0; e < entriesCount1st; e++) {

        // point to the directory entry
        const BYTE* base = DIR_ENTRY_ADDR(ifd1st, e);

        // check for buffer overflow
        const size_t remaining = (size_t)base + 12 - (size_t)tiffp;
        if(remaining >= length) {
            // bad IFD1 directory, ignore it
            return FALSE;
        }

        // get the tag ID
        WORD tag = ReadUint16(msb_order, base);
        // get the tag type
        WORD type = ReadUint16(msb_order, base + sizeof(WORD));
        // get number of components
        DWORD count = ReadUint32(msb_order, base + sizeof(WORD) + sizeof(WORD));
        // get the tag value
        DWORD offset = ReadUint32(msb_order, base + sizeof(WORD) + sizeof(WORD) + sizeof(DWORD));

        switch(tag) {
        case TAG_COMPRESSION:
            // Tiff Compression Tag (should be COMPRESSION_OJPEG (6), but is not always respected)
            thCompression = offset;
            break;
        case TAG_JPEG_INTERCHANGE_FORMAT:
            // Tiff JPEGInterchangeFormat Tag
            thOffset = offset;
            break;
        case TAG_JPEG_INTERCHANGE_FORMAT_LENGTH:
            // Tiff JPEGInterchangeFormatLength Tag
            thSize = offset;
            break;
        // ### X and Y Resolution ignored, orientation ignored
        case TAG_X_RESOLUTION:		// XResolution
        case TAG_Y_RESOLUTION:		// YResolution
        case TAG_RESOLUTION_UNIT:	// ResolutionUnit
        case TAG_ORIENTATION:		// Orientation
            break;
        default:
            break;
        }
    }

    if(/*thCompression != 6 ||*/ thOffset == 0 || thSize == 0) {
        return TRUE;
    }

    if(thOffset + thSize > length) {
        return TRUE;
    }

    // load the thumbnail

    const BYTE *thLocation = tiffp + thOffset;

    FIMEMORY* hmem = FreeImage_OpenMemory(const_cast<BYTE*>(thLocation), thSize);
    FIBITMAP* thumbnail = FreeImage_LoadFromMemory(FIF_JPEG, hmem);
    FreeImage_CloseMemory(hmem);

    // store the thumbnail
    FreeImage_SetThumbnail(dib, thumbnail);
    // then delete it
    FreeImage_Unload(thumbnail);

    return TRUE;
}