HDRI Exterior Lighting with mental ray

[raziel]

Im starting to use this technique to light my exterior renders, and i have some questions. Im using a skylight with a map enviorment (hdr file) and a photometric free light for shadows. The light is sphere shaped and as uniform spherical light distribution. My questions are:

 

-Since im using gamma 2.2, when i open an HDR image do i override it to gamma 1?

 

-Is the free light enough or do i need something like a sunlight to go with the skylight?

 

-In the exposure settings (mr photographic exposure), do i use the exposure setting, the physical scale, or a little bit of both, to darken or lighten my render?

 

Ive attatched some test renders, the first one has an hdri enviorment and a target direct light, the second one is just an hdri file, and the third one as a hdri enviorment and a photometric free light.

 

Thanks in advance!!

[Dave Buckley]

i was looking into this the other day.

 

apparently you can get really good shadows from just your hdr using importons and irradiance particles.

 

with regards to an exposing the hdr correctly . . .

 

when you import the hdr, choose real pixels rather than adjusting white/black points.

 

then enable mr photographic exposure.

 

adjust the ev value to something realistic for the lighting scenario in your hdr (ex. if its a dusk hdr then something like 4.5, if its sunny day then closer to 14)

 

your exposure is pretty much correct then (with obvious adjustments to image control settings)

 

the only other setting you should need to change is the output amount for the hdr, somewhere between 40-75. this will allow your hdr to show up in the background when using the exposure control, with the need to digress from using a physical scale.

 

if you want to match a the sun's position in an hdr then just use a direct light and line it up properly with the sun in the hdr.

 

enable the hdr in the viewport and you should be able to line it up properly

[pixelperfectg]

-Since im using gamma 2.2, when i open an HDR image do i override it to gamma 1?

Most of the time yes. However, there are some HDR's out here that have a sRGB (gamma 2.2) profile. I've found that the Dosch HDR collections I've purchased are one such example.

 

I believe you're using one in your second example (with the torus knot)...that's why the background has no contrast. If this is the case, load the dosch HDR(s) in at gamma 2.2 for better results. Personally, I use gamma 1.8 on the Dosch HDR's so it's not too "contrasty" but that's just me.

[Dave Buckley]

yep sorry forgot to comment on the gamma issue . . . actually jeff's quickstart quide to gamme on the mrmaterials website is a good explanation of the different possible setups and settings.

 

jeff, while your in the building would you agree/disagree with what i said above? i'm still learning myself

[raziel]

Thanks for the comments guys!

 

when you import the hdr, choose real pixels rather than adjusting white/black points.

 

I always choose real pixels and default exposure when i load an hdr image.

By the way, when i use a light to simulate the sun, i try to replicate the kelvin level of the time of day the hdr was taken. Is this required or doesnt have any impact in the render at all?

 

Ive attatched another test render, with a photometric free light and with a 3200 kelvin value to simulate the sun color, and i only noticed a slight difference in the glass ball, which has a more yellowish specular highlight

than with the default kelvin value.

 

Thanks guys!

[pixelperfectg]

jeff, while your in the building would you agree/disagree with what i said above? i'm still learning myself

Looks fine to me. Although personally I would revise the part about using a direct light since the actual direct lights (not referring to the mrSun) in 3ds Max don't create area/soft shadows with mental ray unless a light shader is assigned or someone is using shadow maps.

 

On the exposure deal: Some people prefer to adjust brightness via the physical scale value on the photographic exposure control, whereas some prefer to adjust the output of the hdr/exr itself. The HDR/EXR output adjustment is of course a more localized method of control whereas physical scale adjustment is a more globalized method. IMHO one method isn't 'more correct' than the other as long as the end result is a nice looking render.

 

By the way, when i use a light to simulate the sun, i try to replicate the kelvin level of the time of day the hdr was taken. Is this required or doesnt have any impact in the render at all?

 

Ive attatched another test render, with a photometric free light and with a 3200 kelvin value to simulate the sun color, and i only noticed a slight difference in the glass ball, which has a more yellowish specular highlight

than with the default kelvin value.

I think you're correct to match the color/temp of the sunlight with the HDR. Yes, it will probably be a subtle effect but IMHO the little things like that can really add up to make your renders more realistic.

 

BTW, I think that last render has a very realistic feel to it.

[raziel]

Looks fine to me. Although personally I would revise the part about using a direct light since the actual direct lights (not referring to the mrSun) in 3ds Max don't create area/soft shadows with mental ray unless a light shader is assigned or someone is using shadow maps.

 

Youre right, but im using a square shaped light 2 meters by 2 meters and this gives me some softer shadows, plus i can control the blackness of the shadow.

 

With the last render i posted it was not that hard to blend the objects with the background, my problem now is doing that with a bigger scene, i just cant get the same effect. The objects seem out of place with the background, they are scaled properly, but i cant adjust my ground plane with the ground from the hdr background! (see attachment) Any suggestions?

 

 

BTW, I think that last render has a very realistic feel to it.

 

Thanks Jeff!!

[pixelperfectg]

Youre right, but im using a square shaped light 2 meters by 2 meters and this gives me some softer shadows, plus i can control the blackness of the shadow.

That would probably be a photometric light source. I was referring specifically to the 3ds Max direct lights that Dave mentioned wherein you can't specify an area radius.

[raziel]

That would probably be a photometric light source. I was referring specifically to the 3ds Max direct lights that Dave mentioned wherein you can't specify an area radius.

 

Yes, im using a photometric light, but i will try it a sun light also and compare the results. I tweaked my exposure settings a little bit, what do you guys think?

 

Thanks!

[raziel]

Hi guys, after some tweaking and photoshop, heres what will probably be one of the final renders. Im not completely happy with the background, but it will have to do. What do you guys think?

 

Thanks!

[RevitGary]

I have yet to figure out this HDRI thing. So I have some basic questions.

Do you use HDRI and MR Sun and Sky together?

 

Do all 3 contribute to the lighting solution? Is HDRI only for exterior scenes?

 

 

In regards to your scene... I cant comment much on the lighting but your ground path seems kind of funky the shadows look detached. I assume the planes dont match

[raziel]

I have yet to figure out this HDRI thing. So I have some basic questions.

Do you use HDRI and MR Sun and Sky together?

 

Do all 3 contribute to the lighting solution? Is HDRI only for exterior scenes?

 

 

In regards to your scene... I cant comment much on the lighting but your ground path seems kind of funky the shadows look detached. I assume the planes dont match

 

 

Im using a daylight system, only sun, and skylight whith the HDRI mapped to it. Its the first time im using it, so i cant say much about it either. I think its use depends of the situation, i guess it can be used to render objects that reflect interiors.

 

What part of the scene do you mean? the concrete paths with themselves or with the background image? If it is with the background, i agree, but the concrete paths are all aligned.

 

Thanks!

[RevitGary]

Where the fence shadow hits the dirt then the concrete path the shadows do not align

[raziel]

Where the fence shadow hits the dirt then the concrete path the shadows do not align

 

Thats because the ground has paint deformation and its bumpy, and the concrete is 5 or 6 cm higher than the ground so it looks odd but it is physically correct.

[RevitGary]

If something looks odd in CG it "is odd" and should be tweaked to look not odd

 

Maybe give your concrete material a softer radiused edge

[raziel]

Eheh, youre right I forgot to chamfer the corners, maybe that will help.

[luckymutt]

In regards to your last image, I think it is coming along, and chamfering edges will definitely help.

Two things that scream "CG" (non-lighiting related) is the grain in the background image and the non-grainy CG.

Second thing is the repeating textures, such as in roof, the fence and the concrete.

For the concrete, I'd make a custom map.

For the fence pieces, I'd make about 12 variants for the cross pieces. Maybe more, but with 12 different patterns you may get away with altering the HSV in Max to use them more than once.

[raziel]

In regards to your last image, I think it is coming along, and chamfering edges will definitely help.

Two things that scream "CG" (non-lighiting related) is the grain in the background image and the non-grainy CG.

Second thing is the repeating textures, such as in roof, the fence and the concrete.

For the concrete, I'd make a custom map.

For the fence pieces, I'd make about 12 variants for the cross pieces. Maybe more, but with 12 different patterns you may get away with altering the HSV in Max to use them more than once.

 

 

I have chamfered the borders of the concrete path, and it looks better now. Regarding the boards, yes, youre right, i only have 2 sets of boards made (3 pieces each), and definitely have to do more. With the difference of grain, i really dont know what im going to do, the background is the HDRI image (220mg image file). Maybe ill render the alpha and retoutch it somehow in photoshop...

 

Thanks!

[wannabeartist]

Hi!

 

I've just been studying about exterior lighting for a good part of last week and I'm still confused

 

Nuno, did I understand correctly from your first post, that you use free light for the sun? I have seen other people doing this also and it's still unclear to me if this has some advantages over using the mental ray physical sun?

[raziel]

Hi!

 

I've just been studying about exterior lighting for a good part of last week and I'm still confused

 

Nuno, did I understand correctly from your first post, that you use free light for the sun? I have seen other people doing this also and it's still unclear to me if this has some advantages over using the mental ray physical sun?

 

Hi Vasco. Yes, for the examples with smaller objects i did use a photometric free light for the sun. For the large scale scene, i tested with the the light and with the MR sun, and got better results with the sun, although i have seen great renders with only one light as the sun. The advantage with the sun its that it requires less tweaking, because with the lights you have to change some settings to get the soft shadows that you want, kelvin level of the light, etc. Hope i helped.

 

Here is an updated render of my scene with the corrections that Michael pointed out. Just have to find a better background image.

 

Thanks!

[wannabeartist]

Thanks for the explanation, Nuno!

 

I've been using only the mr sun/sky myself, but I have always wondered why some people choose a different setup for their daylight.

 

I guess you must be familiar with sIBL from hdrlabs and the way they set up these things? I works great with XSI, but apparently the Max version is not quite there yet feature-wise. There are a bunch of other versions also.

[raziel]

Thanks for the explanation, Nuno!

 

I've been using only the mr sun/sky myself, but I have always wondered why some people choose a different setup for their daylight.

 

I guess you must be familiar with sIBL from hdrlabs and the way they set up these things? I works great with XSI, but apparently the Max version is not quite there yet feature-wise. There are a bunch of other versions also.

 

Youre welcome! Like i said, it depends of the situation, and taste of course. For my last scene i prefered the MR sun / Skylight combination, but for the others, Free light / Skylight. Actually im not familiar with any of that, it was all about trial an error, and in my opinion, what ive learn is pretty much the minimum required to light up a scene.