--License
This script is defined as donationware.
If you find this tool useful, and would like to contribute to more development, 
feel free to donate something to the author through Paypal, using emanuele_lecchi@hotmail.com as address.

--Intro
The exposimeter is able to weight out a rendered picture (the sample) dividing it in parts, and assigning to each one a different importance.
It can also be instructed to weight an interval of the pixel values, rather than the whole range, so to avoid blinding/overexposure.
This is in a way very similar in result to what a lenf filter does, cutting away unwanted light frequencies.

--Instructions
VRay MUST be the current renderer, and GI MUST be enabled in a form or the other, or the script will throw up an error, and will not work until VRay is properly set.

If only one Physcam is in the scene, or a PhysCam is selected at the time the script is run, there's no need to select one again from the pickbutton.
Select none, or click "expose all" to expose all the physical cameras in your scene.
You should then select the priority mode: changing ISOs or changing Shutter Speed.
Choose what percentage of the final image should be the sample.
Aim to have a picture ranging from 50 to 150 pixels across at most.It's of very marginal use to go further upward in image size.

Choose which render setting to apply for the EXPOSURE (user settings will be restored upon exposure finish): QMC GI and AA, ideal for outdoors with lots of detail, the current GI settings the scene has, or the fastest ones for both interior and exterior (the default).
It's WARMLY recommended to keep the default settings, as they lead to the most accurate results in the space of a few seconds, even in the most comples of scenes.

The default settings for the Matrix work fine in most cases.
However, clicking on one image section allows to change its weight through the spinner.
The same applies for the pixel range to take into account.
Have a few tries with them, to best discover how each influences the exposure.
In general terms, lowering the MaxBrightness will OVERexpose the section, while raising the MinBrightness will underexpose the section.
That happens because in the first case, the resulting average brightness will be lower, hence the ISO (or shutter speed) will be raised more to compensate.
In the second, the average brightness will be higher (being the darker samples discarded in the calculations), forcing the ISOs to be lowered more to compensate.

The user can choose a preset, should he want to, to try and initialise the matrix metering to something more tolerant to different situations (indoors/outdoors/unweighted, or whole image).

Now it's just a matter of pressing expose, and waiting for the picture to render.
The script will print loads of informations in the maxscript listener (keep it open, or the text will disappear. Max bug...).


--Goodbyes
Please report bugs and issues in the thread you downloaded this from, on the chaos forum.

Thankyou, and enjoy the show!

Lele