IJG library or Windows photo viewer DQT generation

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The question is: how Windows photo viewer generates DQ (discrete quantization) tables? And/or how any editor or application which uses IJG library generates DQ tables? I'm trying to find out the algorithm of recomputing this tables when the image is resaved and parameters with help of which it computes them.

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user3344003 On

The IJG library uses baseline set of quantization tables using the sample one in the JPEG standard (or at least used to). It then uses the "quality" parameter to scale the values in those tables. Off the top of my head, something like quality setting 75 uses the unmodified table. Quality values higher than the baseline scale those values smaller. Lower quality values scale them larger.