[adzling]

hi, does anyone know how the scaling feature of the IBL lighting environment works?

considering I can't see how big the HDRI effectively is to start with (i.e. it has no visible geometry within the maxwell app afaik) the scaling factor seems very arbitrary.

can anyone tell me how people use this?

thanks!

[Half Life]

IBL scaling works in exactly the same way as image scaling works when mapping materials -- you are not scaling the geometry of the sphere you are simply scaling how much of the image appears mapped to it's UV's.

As far as I know there is no possibility to change the size of the sphere geometry... which is why it requires no revoxelization when using Fire.

Best,
Jason.

[adzling]

hmm, well with image scaling on a material you can see how big it is when it's applied to an object.
can't really say the same about and HDRI as it seems very hard to tell which direction the HDRI is "pointing" in the first place.
unless of course im missing something, which is most likely.

[JDHill]

hmm, well with image scaling on a material you can see how big it is when it's applied to an object. can't really say the same about and HDRI as it seems very hard to tell which direction the HDRI is "pointing" in the first place. unless of course im missing something, which is most likely.

In some plugins, it's possible to pre-visualize the IBL environment from within the host application. Where that's not the case, you might want to use Studio to set up your IBL mapping, and then transfer the values back into your plugin.

As far as I know there is no possibility to change the size of the sphere geometry...

The theoretical sphere must remain centered on the camera eye position at all times, so no matter what size you made it, you wouldn't be able to perceive that its size had changed. Most likely, the reason why no revoxelization is necessary is because no physical sphere actually exists.

[Half Life]

Cool -- I did not know that (the lack of sphere geometry) I had always heard it explained as the big sphere... how does Maxwell manage mapping the image to no geometry (and by extension no UVs)?

I can clearly see it tiling just as any image would... I bet there's math involved

Best,
Jason.

[adzling]

thanks for this
can you tell me how the resolution of the HDRI affects the lighting/rendering?

will a low resolution HDRI yield a grainier image for example?

[JDHill]

@Jason: Well, I don't know that either -- so I wrote most likely. It just would not seem to make much sense to generate an actual piece of geometry when you don't need to.

@adzling: I do not think it should make for a grainier image, but I haven't actually tested that. Mainly, it will result in a blurrier or more pixelated background, and will not be capable of producing as sharp of shadows as a higher resolution image.

[adzling]

thanks for all the replies.

when i look at the HDRI images i am using they look like a cube spread out...4 faces roughly with various areas lighter and darker to simulate lighting in a studio environment.

is it correct to assume the center of the image is positioned to face the camera by default or is it indexed some other way?

[JDHill]

No, that assumption would be incorrect -- there may be any number of cameras in a scene. As to how it is oriented by default, a quick check in Studio shows that the center of the image faces positive X (i.e. sighting along negative X, you will view the center of the image), using Studio's coordinate system. I would just recommend opening Studio, loading an image into IBL, and playing around a bit to get the feel of things.

[Half Life]

Those "cross" types of HDRI will not work, you need the "Spherical Map" type -- you can use:

http://projects.ict.usc.edu/graphics/HDRShop/ to convert.

Best,
Jason.

[adzling]

hmm ok JD that's helpful.
when i open the file in studio i can see the HDRI as a background image but i cannot see it presented as a 3d sphere or cube so im not sure how it wraps around behind the camera i'm viewing from or how it wraps around the scene in general.
contrary to your description it's just floating there completely unrelated to the 3d axis...
i had kinda envisioned in my head that an HDRI was a filter that wrapped around the scene, either projecting light or stopping the projection of light depending upon it's grayscale value....that assumption seems to be wrong judging by what i'm looking at.

i can see that by altering the offset angle i can move it left or right, or by altering the second offset angle up or down.
altering the scale rather confusingly multiplies the image (so 2 gives two images) rather than scaling it.

half-life below are a couple of the HDRIs i have been playing with.
is the second one what you mean by "cross" while the former is "spherical"?

if maxwell can't use a "cross" type HDRI (i'm assuming that's a cube with it's facets unfolded) then what does the "spherical mapping" option in the IBL setup do?

[Half Life]

No your images are formatted properly for spherical mapping -- scroll down on this page to see the cross style HDR: http://www.zoobox.co.uk/tut-usinghdr.html

Screen mapping (which is the option in Studio -- your plugin may vary) is useful if you just want to use a flat image as a type of lighting plane... sometime useful if you are doing interior shots and only want enough IBL to be seen through a window.

Best,
Jason.

[Half Life]

If you want to really get how these settings work then using Fire in Maxwell studio is the best way to do so (unless your plugin supports fire)... the vertical offset is not giving you 2 images it is offsetting the tiling, you should think of this as a tiling image that is not seamless in the vertical direction.

Best,
Jason.

[adzling]

thanks jason.

fire doesn't seem to help me much.
i can only see the HDRI only when i tick the "use as background" image option....which is rather pointless.
there doesn't seem to be any 3d preview of the mapped HDRI

i'm guessing your probably reaching your limit of patience with me by this point, so i'm going to summarize the current situation as i think it stands and the corrective action i need to take to tweak it properly...

ok so i'm using the right type of HDRI and it's working as intended by maxwell, yay!

as it stands the output is just too dark...
if i interactively bump the value of the HDRI up using the multi-light feature the whole image rapidly gets washed out.

so i think that means i just need to figure out how maxwell orients the HDRI so i can get the "white" part of the HDRI that is throwing light on the scened oriented correctly so it lights up what my camera view is looking at rather than say the backside of the object....

does this make sense?

[Half Life]

The spherical mapping is setup to rotate via the the offset (horizontal) command -- as is typical this would be 360 degrees around the sphere... I would simply begin rotation (negative or positive) at 15 degree increments until the lighting agrees with your intent... if you are in studio (using fire) simply use control+alt+ middle mouse button on the little slider arrows(next to the offset value) to rapidly move the lighting around the object.

Poor quality (ie free) IBL often does not give good lighting results, so bear that in mind... and the images you've chosen have very little contrast.

Best,
Jason.