Increase slightly the middle level of blue:

curves=blue='0/0 0.5/0.58 1/1'

Vintage effect:

curves=r='0/0.11 .42/.51 1/0.95':g='0/0 0.50/0.48 1/1':b='0/0.22 .49/.44 1/0.8'

Here we obtain the following coordinates for each components:

red

(0;0.11) (0.42;0.51) (1;0.95)

green

(0;0) (0.50;0.48) (1;1)

blue

(0;0.22) (0.49;0.44) (1;0.80)

The previous example can also be achieved with the associated built-in preset:

curves=preset=vintage

Or simply:

curves=vintage

Use a Photoshop preset and redefine the points of the green component:

curves=psfile='MyCurvesPresets/purple.acv':green='0/0 0.45/0.53 1/1'

Check out the curves of the cross_process profile using ffmpeg and gnuplot:

ffmpeg -f lavfi -i color -vf curves=cross_process:plot=/tmp/curves.plt -frames:v 1 -f null -
gnuplot -p /tmp/curves.plt