[yt-users] Consistent brightness in volume rendering movies

[Wolfgang Kastaun]

Hi,

I am trying to assemble Yt volume renderings into a movie using moviepy, 
which essentially takes a numpy rgb array for each frame and produces a 
video.

However, I am a bit confused on the absolute luminosity in volume 
renderings.

It seems that adding annotations via cam.draw_domain() does not only 
draw the domain, but also adjusts the image brightness, which is a bit 
surprising. I did not notice that when using cam.save_image() for a 
single frame instead using the image array directly, apparently the 
former does adjust brightness as well.

I want to avoid rescaling based on average or maximum brightness *of a 
single frame* in a movie, because this is misleading.
The brightness of a pixel should only depend on the data along the 
corresponding ray, not on the other rays as well. Rather, the scale 
should be constant during the movie. I know it is probably difficult, 
but is there a way to estimate a reasonable scaling from the expected 
data range of the whole evolution and the size of the domain? Also which 
other functions besides cam.draw_domain() do implicitly adjust the 
brightness?

Regards,
Wolfgang Kastaun.