Transparency for image-based subtitles

[cest-la-v]

Hello team, is there any setting to set the transparency for image-based subtitles?

I'm using MPV to watch HDR videos with soft subtitle like this one:

Text #5
ID                             : 7
Format                         : PGS
Muxing mode                    : zlib
Codec ID                       : S_HDMV/PGS
Codec ID/Info                  : Picture based subtitle format used on BDs/HD-DVDs
Duration                       : 2 h 3 min
Bit rate                       : 24.0 kb/s
Frame rate                     : 0.314 FPS
Count of elements              : 2322
Stream size                    : 21.2 MiB (0%)
Title                          : English
Language                       : English
Default                        : No
Forced                         : No

The graphic looks great with HDR working perfectly, except for the subtitles are way too bright. I understand that the sub-color can't work on these image subtitles, but what about using transparency to dim it down a little bit?

[hooke007]

almost dup #13680