2004.06.01 08:27 "RE: [Tiff] Tiff JPEG compression quality factor", by Albert Adell

Hi Phillip,

I've tried to write the code with the formula you provided me, but I can't access to the Q-Tables using the LibTiff Library.

I've read in a JPEG-compressed TIFF file the following tags:

-TIFFTAG_JPEGQTABLES: the library returns code 0 that means that this tag does not exist.

-TIFFTAG_JPEGTABLES: With this tag I succeed on reading some values, but I have no idea what they mean. I've looked for it in Internet and I've found that using this tag, the library returns the following:

        u_short*,void** count & tables

My problem is that I don't how to use the void **, anyway the "u_Short" value returns a value of 289... and does not look very good...

What am I doing wrong? Which is the right way to get this q-value back using the LibTiff (the q-value that you refered in your mail as q = cinfo.quant_tbl_ptrs[0]->quantval[6])?

Thank a lot,

Albert