I have tried this approach:
1. Getting the sub/idx files from the DVD imafe with VSRip.
2a. Loaded these files in BDSup2Sub and reexported with the Create new palette option.
- Merged the sub/idx files with the MKV file with mkvmerge.
Well, now the subtitles are white, but the dark shadows are missing. Only a pale gray frame remains. I does NOT look nice.
I have tried a couple of variants, with a changed step 2:
2b. As above, but threshold values are adjusted to reflect the actual color values in the “correct” subtitle images.
- No change, dark shadows still missing.
2c. Loaded these files in BDSup2Sub and reexported with the Keep existing palette option.
- Transparent subtitles as with the simple workflow.
I should add, that out of 9 DVDs so far, 4 have the transparent subtitle problem