Flickering white when using scale and zoompan

[mucikiki]

Summary of the bug:
When I try to zoom an image, if this image has a white background (255,255,255) I obtain an output with a variable white (between 255,255,255 and 255,254,255). It is ok with other colors.

IMPORTANT: this only happens with big scale number, for example scale=12800x7200. It is ok with scale=1280x720.

How to reproduce:

% ffmpeg -f image2 -loop 1 -t 6.2 -r 29.97 -i xxxx -c:v libx264 -profile:v main -pix_fmt yuv420p -level:v 3.1 -crf 24 -color_primaries bt709 -color_trc bt709 -colorspace bt709 -y -filter_complex "[0:v]scale=12800x7200,zoompan=z='min(zoom+0.0015,1.5)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=184:fps=29.97:s=1280x720,trim=duration=6.2[filtered]"
ffmpeg version N-48944-g9b069eb14e-static https://johnvansickle.com/ffmpeg/
built on gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516

Input file: ​https://www.dropbox.com/s/j50lf6we1c6ouvu/esempio%20tremolio%20per%20sito%20ffmpeg.jpg?dl=0
Output video: ​https://www.dropbox.com/s/728fuvdhc2a4gql/esempio%20tremolio%20per%20sito%20ffmpeg.mp4?dl=0

[Carl Eugen Hoyos]

Always provide the input file(s), do not provide the output file unless specifically asked to do so.