Default Shutter Speed?

[coult099]

In the documentation for the hdrfilm plugin, I see: "...the output file will record linear radiance values." I take this to mean that each pixel in the rendered image has units of radiance (W/sr/m^2). However, in the sensor source code, there is reference to variables m_shutter_open and m_shutter_open_time. This leads me to believe that the rendered image actually has units of J/sr/m^2, since we have a time over which the image is captured. Is this correct? Apologies if I have made a basic error here.

Additionally, I cannot see where the variables m_shutter_open and m_shutter_open_time are set to a default value. There is code to be able to set these parameters and read them off from a given sensor, but I do not see where or if they have a default value. When calling mi.render, is there a default shutter speed? Or, should I scale the image by my desired shutter speed to achieve a given exposure? Any insight is greatly appreciated.

[rtabbara]

Hi @coult099 ,

Sensors can be provided with shutter_open and shutter_close parameters during initialisation. They are both default initialised to 0 in sensor.cpp.

However, please keep in mind while Mitsuba 3 does indeed sample rays over the shutter time interval (if you choose to set them), there are currently no native plugins that utilise this information. So for instance, you won't be able to simulate motion blur effects from shapes that move over that time interval.

More importantly, the films that are provided don't simulate the effect of radiant exposure either, so that however long you set your exposure time doesn't affect the final output. You would need to modify or add new sensors to model these additional effects (artifacts) of physical cameras.