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Blabberlicious
11-01-2004, 12:04 AM
Ok people - bear with me on this....I'm not sure if this is a problem, or just a misunderstanding of the concepts involved.

or both...


Been experimenting with using HDR maps for better/brighter retraced reflections.

Using Textured Environment with a HDRI map, but finding that the overall reflections get so massively boosted, that my subtle dirt/grime grayscale refection maps get blasted out. Very tricky to break up reflections generated using these maps.

Know I know that I could just drop the opacity of the Textured Environment/Image world to to 'balance' the overblown reflections, but I'm wondering if this defeats the point of using HDR for reflections in the first place? I end up with Image World Brightness Values of less than 10%.

My interest in this method started after reading excellent tuts on Worms of Art, that show HDRs used for ray-traced reflections. But the emphasis seem to be on boosting refection on Glass and metals. I'm in interested in doing the same for objects with more subtle type of refection.


So my question is...how do I get good control of HDR reflections using hand painted grayscale maps?


Try it for yourself.
1. Slap a HRDI into Imageworld
2. In your test objects surface, create Incidence based Reflection with ceramic type values.
3. Create a second Procedural layer with some Fractal noise to break up the refections - or use a greyscale image map if you have one handy.


All works dandy when using standard rgb maps, but throw in a HDR you get lovely bright refection, but way too intense overall 'wetness' in what should be Zero refectitive areas.

Does anyone use HDRIs for Rayraced refections and care to share any insights/methods?

I'd like to avoid having to re texture for RGB and HRDI maps, but would like to have the option to ray-trace reflection when time allows - and get the best out of HRDIs.

In my gradually dimming brain, I have an vague idea that this its to do with the inability of 8bit imagemaps to dictate big enough changes in value (ie control/clamp) the amount of Refection hitting the object via the HDRI.

oh! Typing that almost gave me a nosebleed!


Anyway, any comments appreciated. I'll post some examples when I've looked into it more.

Cheerio

SplineGod
11-01-2004, 12:19 AM
I tend to use gradients set to previous layer to affect my procedural or hand painted gray scale images and see what they do.

You can also cheat LDR Images to behave like HDR Images.
Create a skyball and place your image in the color and luminosity channels.
Apply a gradient set to previous layer in the luminosity channel on top of the current image map there already. Now set the value on the low end to whatever and then you can change the value on the bright end to way above 100%. That would give you a linear response. If you add a 3rd or more keys you can make the affect nonlinear or clip things at particular levels.

I think whats happening is normal. All surfaces in reality are reflective. It takes something like lamp black to get towards zero reflectivity. Suppose you have a material that have very little reflectivity but you put it into an environment that has an extremely bright light source. You will get hot or hotter areas on your surface.

You might be able to use the same gradient trick to tone down your HDR Images in a more selective way. :)

Panikos
11-01-2004, 02:03 AM
Generally speaking LW Reflection options are limited. You have only :

- 100% Backdrop
- 50% Raytrace + 50% Backdrop
- 100% Spherical
- 50% Raytrace + 50% Spherical

Worley's G2 and Evalsion HyperSmooth give more control.

SplineGod
11-01-2004, 02:09 AM
Generally speaking LW Reflection options are limited. You have only :

- 100% Backdrop
- 50% Raytrace + 50% Backdrop
- 100% Spherical
- 50% Raytrace + 50% Spherical

Worley's G2 and Evalsion HyperSmooth give more control. And fixing it in post :)

gerardo
11-01-2004, 04:16 AM
When you obtain very intense brightness with a HDRI you can adjust the dynamic range of the image (Depth Color) before applying it as Background Image to correct colors and brightness that aren´t look very natural. This adjustment can make it in the Image Editor with HDRExposure and then to adjust the gamma with Full Precision Gamma if it is necessary; if you are also illuminating your scene with this image, you will attenuate the noise usually provided by HDRIs; you should be careful with this method since you can lose those brightness for which we use HDRIs! :)
Also notice that if you only want the HDRI reflections, isn´t necessary to activate RayTracing in Render Panel, is enough with choosing Backdrop in the Reflection Options of the Surface Editor.




Gerardo

Blabberlicious
11-01-2004, 09:53 AM
Also notice that if you only want the HDRI reflections, isn´t necessary to activate RayTracing in Render Panel, is enough with choosing Backdrop in the Reflection Options of the Surface Editor.
Gerardo

Thanks for that, Guys. Much appreciated.

Needless to say, I overlooked a really good explanation of HRDI exposure on the NT Tuts site (duh!).

Gerardo - I guess you need to keep raytraced refections temporarily ON if you want to use FPRime preview as you are texture because it doesn't see the map otherwise.

Cheers

wizlon
11-01-2004, 12:20 PM
Don't forget the importance of using appropriate real world diffuse values. people often use diffuse values that are much to high. use opposite of your reflection gradient.

Mwai Kasamale
11-01-2004, 01:59 PM
You'll also want to utillize the HDR_Gamma control plug.

gerardo
11-02-2004, 12:42 AM
Gerardo - I guess you need to keep raytraced refections temporarily ON if you want to use FPRime preview as you are texture because it doesn't see the map otherwise.

Cheers


Even if you are using FPrime, you don't need it if you use Backdrop Reflection :)



Gerardo

Blabberlicious
11-02-2004, 10:05 AM
Even if you are using FPrime, you don't need it if you use Backdrop Reflection :)



Gerardo

Just to be clear:

FPrime's Preview only displays the HDR relections with 'RayTrace Refection Off' if the particular surface is set to 'Spherical Refection Map' in the Surface Editor.

If you switch the mapping type to Raytracing + Backdrop, it doesn't pick it up - although the surface does seem to pick up some kind of weird illumination boost.

So when you say 'use backdrop refection' could you clarify what you mean?

Perhaps I am misunderstanding you?

Anyway, I guess the advantages of using Spherical Mapped HDR Reflection Via the Surface Editor, rather than a true backdrop image seem to be to allow 'per object' refection assignment, as well as avoiding having to make adjustments to less reflective objects that might react poorly to the high levels of illumination produced by HDRIs.

But heck, I'm making this up as I go along :-)

gerardo
11-02-2004, 04:03 PM
When I say Backdrop Reflection I refer to Backdrop in the Reflection Options of the Surface Editor as I said in my first post.
To be clearer:
In Render Options Panel turn OFF Ray Trace Reflections
In SurfaceEditor/Environment/Reflection Options Backdrop choose Backdrop Only or Raytracing+Backdrop
In Effect/Backdrop/AddEnvironment choose ImageWorld

Notice that you have Ray Trace Reflections OFF, however FPrime's Preview will show you the reflections of the HDRI. As I said in my first post this it is useful if "you only want the HDRI reflections."

Also if you set ' Spherical Refection Map' in the Surface Editor (and obviously you choose a HDRI) you will see the reflections with Ray Reflections OFF or ON indistinctly. :)



Gerardo

Blabberlicious
11-02-2004, 04:33 PM
When I say Backdrop Reflection I refer to Backdrop in the Reflection Options of the Surface Editor as I said in my first post.
Gerardo

So you did! Sorry to be so slow, but I get what you mean. Thanks for clarifying.

:-)

gerardo
11-03-2004, 02:48 AM
This is useful if you only need the HDRI reflections, if not, you would have to activate RayTrace Reflections as you said or to capture an environment map of the scene (you can use Refgen (http://www.kolumbus.fi/erkki.halkka/plugpak/RefGen_frame.html), Special Projection Engine of Juanjosé Gonzáles (http://www.arrakis.es/~juanj/) or Enviro of WorleyLabs (http://www.worley.com/polk/polk_enviro.html)) and to take advantage of the benefits of Spherical Mapped HDR Reflection Via the Surface Editor as you mentioned (you would not need RayTracing!) :)



Gerardo

Blabberlicious
11-03-2004, 11:42 AM
Thanks for those links. Very Illuminating ;-).


Blurring the HDRI refection maps with Full Precision HDR Blur Plug-in works really well. Quite difference from blurring reflections via Surface attributes.

This just gets better & better!

Keep those tips coming!

mercuryrex
11-06-2004, 03:05 AM
Thanks for those links. Very Illuminating ;-).


Blurring the HDRI refection maps with Full Precision HDR Blur Plug-in works really well. Quite difference from blurring reflections via Surface attributes.

This just gets better & better!

Keep those tips coming!Isn't there a problem with that technique though?

What about surfaces in your scene that don't want blurred reflections?
(Or need less/different intensity blurring than other surfaces/materials)

Because that blurring trick wouldn't just apply to the object/surface where you want to limit the sharpness of reflections,...it would be universal and affect everything in your scene that receives a reflection from the HDRI image, wouldn't it?

I have the same problem to figure out as the original poster.
I am trying to figure out how to get great realistic reflections on human skin, such as people like The Ripper manage to acheive.
If I blur the HDRI image to do this, then it will also affect reflections on other objects where you actually want the sharp reflections. (Like chrome, mirror, or ceramic type surfaces).


Tried lowering the intensity of Imageworld.
Didn't work.
Tried messing with surface reflection map,...that didn't work either.
Still get extremely sharp highlights on the skin.
Thought about just mapping the HDRI onto the inside of an environment spehere and lowering the luminosity to take down the high end values a bit. But it's the same problem as with the blurring technique,.....you may have different objects/surfaces, and you want something like metal to take advantage of the HDRI and not have duller reflections, or ones that are just as blurred as other surfaces such as skinlike textures.
Also tried diffusion map, it took down the reflection down alright, but it needed to be so strong to make the contrast less noticable that in certain areas you could hardly see any reflection.

Another problem is that different parts of the human face are more reflective than other parts, which means finding a good way to control things is a very hit and miss affair when you have so many more variables to find out due to getting your surface reflection map to work with the HRI image you use as a reflection. As you need sharper reflections in places, and not in others.
So hard to stop that extreme intensity of the light parts, while making sure that other surfaces in a scene get the benefit from HDRI refelctions that you want.

So hard to do. When people ask what to do about reflection for human face,..they say low reflection value in surface attributes like 2%-5% etc....just doesn't work for me. forehead still looks like a mirror, or extremely oily/wet skin.
The reflection on forhead, I've noticed on real skin, isn't blurred that much,..it's more just slightly less contrasted and takes on the colour of the surface to some extent.

Like I say, you still need the benefit of HDRI reflection on other parts of your scene sometimes.

Some good tips in this thread though, that will surely be useful in general.

Looks like what Larry suggested by doing it in post is the most viable option.
I know post work is good,..but sometimes it almost feels like if you feel you should be able to do something in LW, but can't figure out how, it sort of feels like....defeat.:D

I wish there was a tutorial that directly dealt with this aspect of HDRI reflection maps.

Blabberlicious
11-06-2004, 12:01 PM
Isn't there a problem with that technique though?


If I blur the HDRI image to do this, then it will also affect reflections on other objects where you actually want the sharp reflections. (Like chrome, mirror, or ceramic type surfaces).
I wish there was a tutorial that directly dealt with this aspect of HDRI reflection maps.


I agree, it's an intersting topic. Some of publiucations (like Leigh's excellent book) set out a number of techniques that run into trouble when combined with HRDI refections. Given time (& space) I'm sure she would have expanded on things and come up with some good rules and workflow.

As for selective buri. In theory (I think) - you should be able to Add FP Blur to the Background HDRI in Image Editor, then set it's Mask option to SPECIAL BUFFERS. Then the blur 'should' only be applied to surfaces with 1.0 (On) in the Surface Editors Special Buffer field.

But I fear LW isn't clever enough to do that...and that Blurring applies to the object, rather that the reflection maps it uses.

If this can work, anyone care please step in and confirm? (or suggest another way, other than using duplicate HRDI maps & Spherical only Environment maps.)

If it had any sense, you would also also be able to put a percentage of the burl in the special buffer field - but hey - that's too ambitious for NT :-)

That way you can (could?) at least bur reflections on a per-object basis. I guess you could do the same for HRI Exposure, too.

I say SHOULD be able, but in the time I wanted to spend posting an example, LW crahed * times - usually when opening the Image Editor.

I you run a mac, you know how frustrating this is...


So, HRD refections are great but, you have to seriously dampen refecection/diffuse values, and accept that you are controlling values that far exceed the lowly 0-255 0-100% percentage scale of standard layers. That seems to be the price for have one foot in each camp!


Cheers

gerardo
11-06-2004, 09:49 PM
Yes, you can use a HDRI (without Blur) for Image World and Full Precision Blur (through Image Filter and Special Buffer) for the surfaces; the problem with this is that would blur all the other details of the surface (bump, textures, etc). Maybe in this case Soften Reflections Filter is a better option. :)



Gerardo

mercuryrex
11-07-2004, 02:29 AM
Thanks for that post Blabberlicious

You wrote an interesting post, but I just want to pick out one line if you don't mind me missing out everything else.
"That way you can (could?) at least bur reflections on a per-object basis. I guess you could do the same for HRI Exposure, too."


Later on after I posted my last post, I thought of something that is relevant to your sentence above.
I know that I am thinking a lot in relation to human skin, but the thinking can be applied to various other surfaces too (like leather, or other material).

I noticed that reflections on human skin seem to be less blurred the more reflective the part of the skin is (eg forehead), and the reflectioins appear to be more blurred where the skin is less reflective and more rough.

So,.....You know how you can apply maps to control certain specific areas of certain surface properties such as diffusion maps and reflection maps, right?.....
.....Well is there any way to use the same sort of maps to control reflection blurring?

Then you could use the reflection map in surface properties to say where on the face you want the reflection blurred, and where on the face you want a sharper reflection.

Can we do this?

If we can, it will go a long way to solving many problems.
I would have thought this should be possible anyway.

Panikos
11-07-2004, 04:28 AM
I suggest to add some ColorHighlights setting in the LW surfaces. This will digest white speculars and push the reflection towards the surface color.

Blabberlicious
11-07-2004, 04:55 PM
I suggest to add some ColorHighlights setting in the LW surfaces. This will digest white speculars and push the reflection towards the surface color.


Nice idea - I use that too - very good at clamping down those unruly highlights.

(Thinking out loud)
If you wanted to blend the 'sharpness' of reflections across a single surface, I guess you could set up two surfaces, one with at a burred HDRI Spherical Environment Map, the other 'straight'.

Then use the Surface Blend Shader to blend between then two maps. The cool thing about that shader is you can use an image/gradient to key out it's how it blends with the original layer. That means you can blend in Blurred Reflection maps with great precision.

This is all supposition, but it should work.

:-)

Blabberlicious
11-07-2004, 07:23 PM
Pants!

Tried it....

and Surf Mixer doesn't take the environments map into account when Blending between Textures (or the bump map for that matter :-(

That's a shame, because you could do some lovely stuff.

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