[Josephus Holt]

In VRay there's a way to place a background image (not IBL) in a frontal view, like when we put an hdr in the environment tab as a "screen map". Does Rhino/Maxwell have anything like that, where I could use an image for the "screen map" (not to be used as an IBL) AND use the physical sky?

In C4D I can make objects invisible to the renderer, i.e. put a plane in the way of the sun and not have it block the sun(light). Can I do this with Rhino/Maxwell?

Joe

[JDHill]

On the first question, yes, if you go to Scene Manager > Environment, switch to Image Based, and then un-check Use Background for all Channels, you can specify that you only want to use the Background Channel - that channel does not contribute to the scene lighting; it's just a background image. Next, look at the bottom of that page and set Disabled use: to Physical Sky. Now, check the Screen Map box in the Background Channel. That should get you where you are asking to go: a screen-mapped background image, with lighting coming from Physical Sky.

On the second question, I'm not sure -- I don't think there's any way to hide the sun from the camera. Probably, it would be easiest to accomplish this by not using the sun, and instead using an emitter with Hide to Camera set in the Maxwell Object Properties page. I might be misunderstanding the question though.

[Josephus Holt]

Thx for the answer on the first question, I tried that out. I find the language "Disabled use" confusing...does that mean if the illumination channel is disabled, then use whichever is selected? I checked the manual but it did not clarify that for me. I don't suppose there is an option to use that background channel ALSO as an illumination channel as that would give me the opportunity to control the light of the map?

On the second question, if I'm using a large vertical plane in lieu of using it in the background channel as a screen map (by assigning an mxi I can control the light value of that background image), that tall plane could possibly block the sunlight from coming into the room, hence I was looking for a way to make it transparent to the sun (so the sunlight went right through that plane) but visible to the camera. (I'm not looking to block the sun...in fact I'm asking for the opposite) Can I do this?

[JDHill]

Yeah, the naming of that parameter seems to have become a bit unsynchronized over time...the UI says 'Disabled use', the plugin manual does it a bit better, calling it 'Disabled Channels use', and the interactive help (which you get by clicking the little help icon at the top of the Scene Manager) is even more verbose, calling it 'Disabled Channel Environment' and telling you that 'The selected environment type will be used in Image Based Environment channels which are disabled'. I'll try to get this fixed up next time around.

As far as doing what you are actually trying to do, I feel like I am trying to answer small little sub-questions of one overriding, yet unknown, larger question; I'm starting to get an idea of what you're doing from your second paragraph, but I still don't know why you're trying to do it. So, why don't we back up a few steps and get the long view on what it is that you're trying to accomplish, and why you feel the need to do it this rather convoluted way. Maybe it's necessary, and we can fine tune the method, but maybe it's not, and we can save ourselves some wasted effort. Generally, if you find yourself fighting a system this hard, it's not going to work out well, and this will show up in various ways in the final result.

[Josephus Holt]

As far as doing what you are actually trying to do, I feel like I am trying to answer small little sub-questions of one overriding, yet unknown, larger question; I'm starting to get an idea of what you're doing from your second paragraph, but I still don't know why you're trying to do it. So, why don't we back up a few steps and get the long view on what it is that you're trying to accomplish, and why you feel the need to do it this rather convoluted way. Maybe it's necessary, and we can fine tune the method, but maybe it's not, and we can save ourselves some wasted effort. Generally, if you find yourself fighting a system this hard, it's not going to work out well, and this will show up in various ways in the final result.

I like your approach here, JD. First this is in connection with the interior family room render you saw in my other post.
I'm looking for two things here, the first is to get some decent exterior lighting for the part that is visible through the windows as well as bring in some of that light into the room, but I want this light to be with real world settings so I can tell the client "this is approximately what the light in the room will feel on March 21 at 8am". It is quite likely that he will ask for another render for another date and another time.
The second is bringing in the background image of the site (which unfortunately was not considered when I "snapped" the picture when visiting the site very early in the project, before I even knew I was going to do these renders). Although I made the image into an hdr in Photoshop, when I use the same map for illumination there is way too much green in the light due to all the foliage, besides the fact that the light source is not "physically" close. Another aspect of the background image is that I want to be able to control the brightness so I can adjust with the darker interior image. Below is the image I'm using.

[JDHill]

Well, there are a couple points of entry when it comes to adjusting the brightness of the background; you can adjust it when you convert from jpeg to hdr/mxi (I might also try using maxwell.exe for this, rather than photoshop), and you can also adjust the Intensity parameter in the Background channel. That's just for adjusting how the image looks, as it will not be contributing to the lighting of the scene.

Aside from that, what I'd do first would be to build a very simple scene; just a plane and a few spheres. I'd then play with the physical sky a bit until I had something similar to what is present in the photo (check the plugin manual to see some examples of what does what) when it's close, put the image in the Background channel and see how good of a match you have. At this point, you are lighting the scene with Maxwell alone; you can decide how you'd like to get the background in the image at this point, whether that means using the hdr/mxi in the Background channel, creating an mxi emitter material, or creating a normal material that uses the original jpeg -- remember in that case that you also have the image manipulation controls (saturation, brightness, etc.) in the texture.

Depending on how the shot works, it might be best to try to use a screen mapped Background channel, since it's the lowest maintenance method; no extra geometry to worry about positioning. On the other hand, you may have better/easier control either mapping the image on individual back planes outside the structure, or as I've done once or twice in the past, building a cylinder that surrounds the house; in that case, it's pretty easy to sync up the image with the sun, just by adjusting the tile/offset in the texture where it's assigned.

You should be able to avoid (and I think this is the main thing you were looking for with the previous question) having the cylinder cast shadows by checking the 'Hide from GI' switch in Maxwell Object Properties. Keep in mind that this isn't going to be the easiest project - in cases where you can use a professionally produced hdr, which maps spherically and was taken/converted with this usage in mind, that you will have quite a few less restrictions. But that wouldn't be the actual site either, so you'll just have to make do -- make sure to take notes about what gives you the most trouble, so that you can have an easier time of it next time you are shooting background image(s) that will be used for this sort of thing.

[Josephus Holt]

Thank you JD, as always, for the thorough reply.

Of the choices you list I think the one that gives me the most flexibility is mapping it to a cylinder, and the part about hiding from GI is what I was looking for (I think C4D calls it "hide from sun"...which with my limited mental abilities was easily understood). By making it an mxi (which I did) gives me a lot of flexibility.

I ran another render with the image in the background slot and enabling the physical sky. Since the background image is seen from a fairly dark interior it would require several iterations of going back to the image and brightening it up until it was right, so I don't find this to be a particularly appealing option.

I like the suggestion about builidng a very simple scene to match the physical sky with the background. After you mentioned that I looked more closely at the image and realized it was taken several hours later than the early morning time I set for the physical sky. I'll test this out maybe tomorrow as we're supposed to get more snow in Nashville....just a few inches seems to keep us all home

[Josephus Holt]

Update: setting up a "demo scene" really worked well. Was able to get the physical sky to produce light and shadows that matched the hdr image quite well. Thx much, Joe

[JDHill]

Glad it helped - I was also going to mention, that there is an Intensity parameter in the Background channel, and this should help a bit with lightening/darkening without having to go back and regenerate the image.