As I am trying to get most out of the images it does not make much sense to me to work without a visual control mechanism as every image needs different parameters to get most out of it. So, no, at the moment there is no batch tool available.
A WordPress plugin is on my todo list for a loooong time but unfortunately I can't say when it will see the light of day.
As far as I know, the problem only exists with Adobe Photoshop, which is why there is a setting in compress-or-die-expert-mode to make the file output photoshop compatible. The file then becomes minimally larger. So if you want to be on the safe side, activate this setting. However, I have never heard that the problem exists outside of Photoshop.
Photoshop actually uses its own quantization tables and its own scaling values for the different quality values. When I mention values, they actually always refer to the standard quantization tables, which are also used by very many programs, as well as the scaling function suggested by the JPEG specification.
Below is a table that shows how the values relate to each other (determined with Photoshop 2023, Version 24.1). The first value in the "Standard Quality" table corresponds to the luminance value and the second to the chrominance value.
Caution: From time to time Photoshop's quantization tables change slightly, so there may be slight variations.
|Photoshop quality||Photoshop Color Subsampling||"Standard" quality|
|Photoshop "Save for web" quality||Photoshop Color Subsampling||"Standard" quality|
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