The original DPX file of Kuruvi has crushed black and high contrast levels (except song sequences). It’s what the director wanted as he supervised the DPX process - which was what the blu-ray was made from.
The film was also shot on various cameras (Super 16mm, 35mm) which highlight the detail problems you mentioned. During post production the "Super 16mm" scenes went through NR process to remove unwanted film dirt. This impacted on the detail. Again, this was on the DPX file. (Tamil film-makers produce their films on a shoebudget - you'd be surprised!!)
The blu-ray actually presents the film more truly then the theatrical showing (which was too muddy thanks to prints being incorrectly made by the labs).
Its not my job to improve the director's vision - only to truly presented it

ALL Ayngaran blu-rays have done this and will continue to do so (while I am there....which may not be for long - more info coming soon).