Setting a target quality before extraction of frames from a video

[Shao85]

Hi, I wonder if wouldn't be possible to do something more for keeping a quality on a maximum. From what I've noticed - Flowframes (v1.36) lowers quality when converting from an UHD video to a *.png files when generating frames. This happens even in the UHD mode.
When compared frames generated using custom ffmpeg command with the same frames extracted by the Flowframes, a number of unique colors was about 4x smaller for the Flowframes ones.
Also, considering the size of an interpolated frames when using a good quality frames as an input - some kind of a quality reduction probably happens even during this step. Wouldn't be possible to add some more options into the settings to prevent that?

The custom FFMPEG command I use for the hq *.png output is:
ffmpeg -i input.mov -vf zscale=matrixin=2020_ncl,format=gbrp16le -pix_fmt rgb24 %09d.png

Theoretically, the same results as above should provide also following command (I preffer the 1st one):
ffmpeg -i input.mov -sws_flags bitexact+accurate_rnd+full_chroma_int -pix_fmt rgb24 %09d.png