Hmm. I've got a file that compresses better with Tak Normal than Tak High /Extra High.
...
Interesting. Thank you!
This can happen, because the encoder only estimates the effect of some compression methods and sometimes this fails and it makes the wrong choice. Most probably it is applying the Prefilter although it hurts or it is using more predictors than neccessary.
I had the opportunity to test (a part of) the file.
First the compression ratio for any preset, each with default and maximum evaluation:
Standard Max (Evaluation)
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Turbo 42.93 41.99
Fast 42.87 41.55
Normal 41.73 41.37
High 42.54 42.34
Extra 42.21 42.06
There is something in Max evaluation which really helps Fast: 1.32 better compression. It is also present in Normal default, where the advantage of Max is much smaller.
Let's find out what in evaluation max is responsible. Try Fast with each single option that would be added by evaluation max:
Fast (default) 42.87
Channel decorr.: Check Both 42.87
Channel decorr.: Mid/Side 42.84
Bitcoder: Optimize choice 42.81
Partition resolution: 256 42.77
Partition Calc.: Validate 42.65
Optimize Quantization 41.98
Fast + Max 41.55
Sorted by compression.
Obviously "Optimize quantization" is the winner. That's very rare and therefore very interesting for me.
Now for High. Let's use maximum evaluation and play a bit with the PreFilter sensitivity:
High + Max 42.34 (Prefilter medium)
-Prefilter low 42.27
-Prefilter off 41.22
Huh, better disable the PreFilter for this file...
Well, sometimes my fast parameter estimation fails. I will evaluate this later.