2004.05.11 19:02 "Re: [Tiff] libitff", by Andrey Kiselev

I am trying to use libtiff and add a tag. Can somebody explain to me the field_oktochange and field_passcount in the TIFFFieldInfo structure. What are they used for? Would appreciate an answer ASAP.

Some tags has influence on how the image should be written (for example, it is TileWidth and TileLength parameters), some other tags has nothing to do with image (such as Artist or Copyright records). The first type of tags should not be altered once written and has FALSE in field_oktochange. The second type can be changed in any time, we set TRUE in field_oktochange for them.

field_passcount defines the need to pass the number of data values in the buffer. If it is TRUE such a tag should be set using call

 TIFFSetField(tiff, tag, count, data_array);

where 'data_array' has 'count' values. It is used for tags when we don't know how much data items they will contain in advance.

Andrey

Andrey V. Kiselev
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