Jump to content
Sign in to follow this  
MikeB

HDRI / Lighting Questions

Recommended Posts

Hello all, I have a few questions.

I've just upgraded to 12.5 and have been playing with the radiosity and HDRI, first off it's really cool. Second, I've quickly realized how much I was having to tweek textures to get them to appear realistic using the ray trace engine under 11 and previous versions.

So here's my questions

1. All the free HDRI resource I've looked at seem to have a fairly low sun angle. Is there a reason for this? For the Architectural renderings that I do, I really need a higher sun angle than what I've been able to find. The finished renderings always look like dawn or dusk.

2. Does it make sense and is it possible use a HDRI background that is simply the ambient sky illumination with no sun and use a directional light to create the primary shadows. If so, does anyone know where I can find or how I can create a simple HDRI for the ambient illumination. It seems to my simple brain that this would give me the benifits of the HDRI technology, but I can keep the controll of the primary light source for the model as I've always been able to do.

Any thoughts appreciated

Thanks

Share this post


Link to post

I posted a message with a very similar question the same day but it didn?t show up in the tech forum, neither did you receive any reply so I thought i had to find out for my self. There are sure other, maybe better ways to do this, but it works. To create an even skylight is quite easy.

1. Create a hemishphere

2. Place a point light in the center with shadows turned off

3. Use emitter and turn up the light to 2000 lumens, give the light a color other than white, for example light blue to simulate the sky.

4. Place a camera right above the center point facing upward on the screen in plan view. Go to camera view

5. Render using Best quality RenderWorks

6. Export as HDRI with a low number of pixels, let?s say 128x128 and give the file a name.

Thats about it. Now you can make a background with this HDRI file and get nice smooth shadows fast.

If you want a sky that is not evenly colored it`s a bit more complicated, but mainly the same. For a sunset sky make the point light a bit darker blu, then aim an orange spotlight towards the horizon and continue as the previous example. You may have to experiment more on this to get the right colors, brightness and light angles.

Share this post


Link to post

DAve,

Will this give the ambient sky illumination w/o a sun source?

Thanks

Share this post


Link to post

6. Export as HDRI with a low number of pixels, let?s say 128x128 and give the file a name.

I had no idea we could make our own HDRIs. What export option is being chosen here? An image file? what format to use as an .hdr?

thanks, mmm

Share this post


Link to post

hans + mark

the HDRI export is proving quite interesting.

i have followed hans' example + am fooling around with the 'ambient' point light colour + with the focus of the 'sun' spotlight.

however, i think NNA could make life a little easier by adding a FAQ here to describe what HDRI is actually useful for. everyone points off-site to technical or theoretical explanations that bear almost no relevance to using the tool in vectorworks. as far as i can figure it can be used for generating atmospheric lighting + shadows to external scenes and/or generating environment backgrounds to scenes.

the environment backgrounds do not seem very usable in terms of image quality + memory usage <in my experience under win XP it's ridiculous>, but the lighting aspect of it is VERY useful!

1

from generating my own HDRI's in VW from hans' example i think we need explanations as to what 'angular', 'vertical cross' + 'panorama' do <my test files come in as different types from the same export source file?>

2

in creating the source file, does the spotlit point on the inner face of the hemisphere become the source point of the lighting when exported or does the spotlight beam remain the sunlight beam.

3

if the point of light on the dome is the 'sun' how do we control it's angle when exported? for instance my 'sun' in the source file is directly overhead and the camera is pointed directly upwards <sun is in the middle of the image> but after exporting as HDRI and used as a background in a new file the sun is down on the horizon...

any guidelines from dave donley would be valued!!!

thanks

Share this post


Link to post

Gideon

I really agree, Nemetschek shold supply a tutorial and a an explanation of how HDRI works. What I?ve found out so far is:

1. How an environment is correctly mapped onto either a sphere or a cardboard box (which seems to be the case with vertcal cross) seems quite complcated.

2. What I did was simply creating a light dome where the lower part is black (since architectural models normally stand on a ground that blocks light from below). The upper part is mainly light blue with an orange spot. This is a very apporximate solution but I think it gives a very nice "moody" sunset look.

2. It?s the lit surfaces that show up on the HDRI background, not the light sources. I think it would be a bit tricky to "syncronise" a directional light to the spot on the background accurately.

3. HDRI seems to work best with exteriors. With interiors where light only comes in through the windows the major part of the light is blocked by roof and walls and the result gets too dark and grainy.

Hans Jakob

Share this post


Link to post

Hello Gideon:

You are correct about what HDRI files are useful for. As the HDTV format adds more pixels to a TV image, HDR makes each pixel more "deep" in its color resolution. The main use of this added color depth is to capture the wide range of brightness that occurs in the real world. This is accomplished by capturing multiple exposures of a scene and stitching them together into a single "deep" HDRI file. You have to use a separate application like HDRShop or Photosphere to do this stitching.

Note that you can use the HDRI file formats (HDR and OpenEXR) to store 2D images, i.e. non-panoramic images, but almost all HDRIs are used as lighting sources or backgrounds for 3D renderings right now.

The panoramic HDRI can be used as a 3D background that surrounds the model (it's like putting a huge textured sphere around the model), for generating a bunch of directional lights at the pixel locations, or both. You can set the layer to use an HDRI for lighting and a plain color for the background, for example.

1. LightWorks automatically detects and determines the format from the locations of the black pixels in the imported HDRI file. If the black pixels form a circle around the image then it will be set to Angular. If there are black squares making a vertical cross then it is that type. Otherwise it is Lat/Long. These are all ways to map a 3D textured sphere to a 2D plane. Lat/long is probably the best because it uses all the pixels and the distortion is limited to the poles. Note that you cannot create a true Angular HDRI without some other package like HDRShop ($), because a rendering of a mirrored sphere is not the same as the angular format, even though they look similar.

2. I think what MikeB is talking about is to use an HDRI to handle the "sky" part of the lighting and a regular directional light to handle the "sun" part. This is a good and appropriate use of the feature. If any very bright spots are in the HDR image then they will by nature become sun-like directional lights, but it is a common technique to separate out these very bright sources from the HDR image. Paul Debevec (the father of this stuff) used conventional light objects for several of his HDRI movies; the Parthenon movie (http://www.debevec.org/Parthenon/) used a regular directional light for the sun and the FiatLux movie used conventional area lights in the stained-glass windows (http://www.debevec.org/FiatLux/).

3. The imported HDRI images assume that you are looking at it from a front view (0 degrees means front), so if you are exporting then importing a VW-generated HDR image set your view up that way when exporting.

Hello Hans:

1. If you want to export a rendered environment and use it for an HDRI, the easiest way would be to create a 100% reflective sphere (the Mirror reflectivity shader with the Mirror factor at 100%), and a camera that aims at it with a narrow field of view and square 1:1 aspect ratio, then render and export that as HDRI using the marquee option. This will produce a "mirrored ball" format HDRI image. However, LightWorks does not support that format directly yet. You could change the mirrored ball into a true angular format using HDRShop, but that will cost $ as the free version of HDRShop doesn't read EXR format files. If you only want a single color or if you do not care about the distortion that will occur from using the wrong format, like if you are only using the HDRI for lighting and not for a background, then you will be fine saying you mirrored ball HDRI is an Angular format image. If it is rendered as a background you will see some distortion because it is not really an angular format.

2. You can also create a image that is twice as wide as it is tall (1:2 aspect) and tell RW that it is a Lat/long format image.

3. You are correct in that there is excessive noise when using HDRIs for interiors. For now it is recommended that they be used for exteriors, or for partial interiors where the light is not trying to thread its way through narrow holes in the model.

HTH,

Dave Donley

dave@nemetschek.net

Edited by Dave_Donley_At_Home

Share this post


Link to post
What export option is being chosen here? An image file? what format to use as an .hdr?

Sorry to be so dense but I'm still looking for how to export to the .hdr format.

TIA, mmm

Share this post


Link to post
You can set the layer to use an HDRI for lighting and a plain color for the background, for example.

I was wondering about this. How is it done? Also, can an HDRI be used for lighting and a different image (of a site for an architectural rendering for instance)be used in the background? It seems you have to choose only one RW Background image.

I think what MikeB is talking about is to use an HDRI to handle the "sky" part of the lighting and a regular directional light to handle the "sun" part. This is a good and appropriate use of the feature.

This is how I'd like to use HDRIs as well. Can somebody explain or point me to an example of what type of HDRI and Directional Light Spec to use.

cheers, mmm

Share this post


Link to post

dave

thanks for the comprehensive reply.

i've been trying out making skydomes with the spotlit sun at various heights + colours to export as HDRI's for use in my models + will try your suggestions re reflectivity etc...

one other thing i've found, that is not made clear, is that you can have 2 HDRI's affecting a scene, one as an environment background + one as ambient lighting.

this is useful as, for example, a blue sky environment used as lighting casts a blue tinge over everything, which isn't always that appealing wink.gif

to use HDRI's this way, zero the saturation + brightness on the 'render background' used for the environment. then in 'layer lighting options' set a different HDRI 'environment lighting' to suit.

this lets you have, say, a blue sky HDRI environment background with a warm yellow HDRI lighting...

have fun

Share this post


Link to post

This is how I'd like to use HDRIs as well. Can somebody explain or point me to an example of what type of HDRI and Directional Light Spec to use.

If you look at the images I posted in this thread

The Morning and Night renders were a single directional light set with the Sun position, and the same (setting sun)HDR rotated about 170 degrees to match the shadows from the Sun in the morning and evening.

hth

Share this post


Link to post

Mark,

To use a different HDRI background from the rendered background, go to the ambient lighting settings under the View menu, LIghting, set layer lighting options.

Share this post


Link to post

Photomatix has an unwrap mirror ball facility, which works well and is free!

http://www.hdrsoft.com/

It should be pretty easy to set up a 100% mirrored sphere, a RW camera with a 1:1 aspect pointing at the sphere with a narrow field of view (making the sphere pretty small can accomplish this), and a 2D unfilled square around it aligned with the camera view's perspective crop rect to make the export marquee snapping more accurate. Put these things in a reusable symbol that you could drop into any model, change to the camera's view, render in a RW mode, and export the HDRI. Unwrap the mirror ball to lat/long format in Photomatix, then re-import as a RW background for use in other projects.

Dave Donley

dave@nemetschek.net

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

 

7150 Riverwood Drive, Columbia, Maryland 21046, USA   |   Contact Us:   410-290-5114

 

© 2018 Vectorworks, Inc. All Rights Reserved. Vectorworks, Inc. is part of the Nemetschek Group.

×