Author Topic: EV target / Camera settings...  (Read 190 times)

Offline Njen

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EV target / Camera settings...
« on: April 13, 2018, 05:40:25 PM »
Will Terragen ever get camera settings like f-stop/shutter/ISO?

If not, what is the EV of the default scene that Terragen ships with? I need to render out spherical HDRI's to a specific EV target, for example '13', but I'm not sure how to make sure that I get what I want.

To be clearer, an EV of 13 is roughly light on a cloudy day, so sunny scenes when using an EV of 13 will look over exposed to the eye, and dark room interiors will look underexposed to the eye. I know I can obviously either expose the image in the camera node up or down using the 'Light Exposure' value, but I don't want to guess what value to set it at in order to have it appear to the exact EV target I require.
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Offline Matt

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Re: EV target / Camera settings...
« Reply #1 on: April 15, 2018, 02:21:29 AM »
Hi Ryan,

Although the maths for calculating EV is straightforward (each EV increment doubles or halves the brightness), there is an unknown scaling factor which we need to map from a sensor input to a value in the EXR. I don't know what that factor should be. Pixel values in an EXR are unitless. The only way I know how to do this is to calibrate Terragen's exposure amount by comparing Terragen's EXR output against the particular EXRs/HDRs you are generating from your other source.

How are your EXRs/HDRs generated (from your other sources)?

Has this scaling factor (a constant) been standardised in other physically based renderers? In other words, do all renderers that have physical camera modes output the exact same EXR values for the same EV and luminance settings? If they do, and I can find documentation on this, I can get Terragen match or provide a conversation table. Otherwise the best I can suggest at the moment is to calibrate Terragen's exposure settings by comparing Terragen' EXR output against whatever you're trying to match.

Matt
Just because milk is white doesn't mean that clouds are made of milk.