Can someone explain HDRI intensity?

RexRed

Can someone explain HDRI intensity?

Some HDRIs create long and dark shadows when shining through trees and some are very diffused and have a gray contrast.

How can I tell by looking at a jpg which HDRIs will have shadows, and which won't?

How would I edit a HDRI that is dull and does not create shadows into one that creates hard shadows?

Can an HDRI be changed as such in the environments tab and if so which parameters would facilitate this change?

I know an HDRI can be brought into Photoshop and edited also and then saved as a HDRI, any tips on changing it there?

Or maybe just adding some distant lights to the scene to emulate a hard shadow effect?

It seems the hard shadows are usually lights that are low to the horizon but I am not sure. 

Any thoughts on this?

Fishtales

If there is no bright area in the HDR, like the sun or street light, then there wont be strong shadows. Also the lower the bright area is to the horizon the less shadow it will cast. To get a stronger light then use a Distant Light in the scene shining from the bright area towards your objects. Some HDR also don't cast shadows because the photographer has taken it inside the shadow area so the light is flat.

RexRed

Fishtales said:

If there is no bright area in the HDR, like the sun or street light, then there wont be strong shadows. Also the lower the bright area is to the horizon the less shadow it will cast. To get a stronger light then use a Distant Light in the scene shining from the bright area towards your objects. Some HDR also don't cast shadows because the photographer has taken it inside the shadow area so the light is flat.

Hmm Fishtales, that explains a lot.

If I were to edit the HDRI, if I put a white or close to white dot in the HDRI, Which would create a harder shadow a small dot or a large dot? 

I need to test this out.

Adding a tropical beach into the scene would give me trees that could cast shadows on the sand and be a good way of answering this question.

I am just wondering if you know the answer to this.

If Ii want the light to be intense, maybe lower the brightness of the HDRI so the white dot is magnitudes higher in brightness.

Then if I raise the HDRI intensity in the environments tab it will get even brighter.

This is a field of inquiry worth exploring.

I suppose even just using a sphere in a scene would also be a good indicator of shadows.

Thanks for your help Fishtales, it has inspired me to test this out and pursue this even further. 

The distant light is a good idea as well, that should be included into any "experiment". 

Thanks for the help! 

Fishtales

RexRed said:

Hmm Fishtales, that explains a lot.

If I were to edit the HDRI, if I put a white or close to white dot in the HDRI, Which would create a harder shadow a small dot or a large dot? 

I need to test this out.

Adding a tropical beach into the scene would give me trees that could cast shadows on the sand and be a good way of answering this question.

I am just wondering if you know the answer to this.

If Ii want the light to be intense, maybe lower the brightness of the HDRI so the white dot is magnitudes higher in brightness.

Then if I raise the HDRI intensity in the environments tab it will get even brighter.

This is a field of inquiry worth exploring.

I suppose even just using a sphere in a scene would also be a good indicator of shadows.

Thanks for your help Fishtales, it has inspired me to test this out and pursue this even further. 

The distant light is a good idea as well, that should be included into any "experiment". 

Thanks for the help! 

To check the shadows from an HDR then look at the shadows that are baked into it and that will show how dark they are. To increase or decrease the intensity of the shadows from the objects you use in the scene then use the Ground Shadow Intensity under Render Settings/Environment/Ground, it might be hidden show use Show Hidden Properties to see it. This only affects the ground shadows and not the shadows from object onto object in the scene. You can attempt to darken/lighten those using the Crush Blacks slider under Tone Mapping, although that makes all the blacks in the scene either lighter or darker, you then have to balance that with the other sliders as mentioned above :)

nemesis10

A very quick clarification.  Imagine an HDRI which looks like a white dot in a black background; this is deceptive since the white dot is really an area of ultra high "whiteness" that the human eye can't see.  Thus the white dot can act as a light source while a simple white dot won't. For example, in a HDRI that has a sun and white houses, only the sun acts as a light source since it is a spot of high dynamic range. The sharpness of the area of high dynamic range decides how sharp the shadows are.  There are tutorials of how to adjust HDRI's in image editor which are worth looking at since it is highly specialized. Here is one that directly answers your question: https://hdrmaps.com/blog/tweaking-hdri-in-photoshop/