HDRI size and IBL

[Guest]

I have a HDRI image that is 4096 x 1011 when I apply this HDRI to a Vray light dome, how far or near is the actual image from the centre point?

For example if I create a box in the centre and then create a half dome sphere that has diameter of 10 metres, then apply the HDRI map to it. I know that the HDRI map will be 5 metres from the box.

But because you cannot determine the diameter of a Vray light dome how can I be sure that the HDRI image is not really far away or really close to the centre object? Because this would affect the size of the reflections, no?

Furthering on from this, when I add a HDRI map to the viewport background to align the HDRI with a photo, the HDRI remains full size of 4096 1011. Resulting in the HDRI viewport background being clipped, which makes me think the HDRI is too close to my centre object?

How does this all work? I simply wish to see my HDRI in my viewport background not clipped and at the right distance from the centre object which would be where I was standing when I took the HDRI.

In the attachments you can clearly see that in my viewport the blue van is very close where is in the actual HDRI



If you look at the shadow of where I was standing the blue van is in the distance.

[simmsimaging]

I am pretty sure the dome is an infinite distance, meaning that light intensity is the same regardless of where your objects are. It's one of the things that give IBL-only images their look. It's different if you map it to a sphere as you describe, and that is what you would have to do if you wanted to play with the relative distance between different objects and the image.

Regarding how the image maps to the viewport, I think the problems you are having may be because your map is not the correct format for correct spherical mapping. It looks like your image would actually map cylindrically. I am not sure if vray dome lights can map that way.

You can probably resolve both your problem by mapping your image to the inside of a cylinder.

[Guest]

So how can I see how the hdri is mapped onto the vray light dome? Currently I am unable to align the hdri map used in the vray to the background, what would be the correct shape so that the hdri fits within the viewport?

I am trying to follow this video http://vimeo.com/17829037 but do it inside of 3ds Max and Vray. when he is alighing the hdri image in teh viewport is is not as zoomed in/cropped as mine is.

[simmsimaging]

I don't use C4D and don't have time right now to watch a 1/2 hour tutorial to see how it all differs, but you should probably do a bit more research on spherical panorama format and there are tutorials around the web for doing IBL with Vray. Maybe check out the SmartIBL website for some basic resources, and some example image maps in the correct format. It's a good site with lots of useful info.

http://smartibl.com/sibl/index.html

/b

[Guest]

so the viewport background would need a spherical image to display it at the correct scale, if a none spherical image is used it will not align in the viewport.

[stef.thomas]

There are quite a few things wrong with your approach/understanding here, it's hard to know where to start. First of all, it's not really an HDRI at all is it? What I mean is, are you confusing the terms HDRI (High Dynamic Range Image) and panorama? It looks like you just spun around and took a bunch of snaps on a point and shoot. Which is fine, but it isn't an HDRI. Secondly, as you have created a cylindrical panorama then you have to map it cylindrically in your scene (I am assuming that your panorama covers a 360° field of view). The best way to do this would be to create a plane with the same dimensions as your image, make sure it has plenty subdivisions then apply a bend modifier to make it form a circle. That way you won't get stretching of the image. Then create a vray light material using your pano and apply it to the cylinder you have created.

The closeness of the van is due to the fact that you aren't using the same camera focal length in your scene as the one which took the panorama. You have to match this or it won't look correct. The car should also be placed the same distance and location in your scene as it would have been from the point you took the panorama from. The main thing I am wondering is why you are using the panorama as the background in your render? The usual way to set this up would be to use the pano as your reflection environment but to then have taken a seperate photo as a backplate, making sure that the orientation matches in your scene. It would be much easier to match up your viewport with a single image rather than an environment map. If you didn't do this at the time then it may mean having to redo your pano to get the same lighting conditions for both. At the moment I don't think the panorama is giving you sufficient quality as a background.

Hope some of that helps.

[Guest]

Thanks for the reply, what I am doing is:
I have taken a photo of where I would like to car to be in situ.
I have then put that photo in the viewport background so I can camera match the photo.
I have then taken a 360 degree pano from the same position that the car is being placed.
I have then turned the pano into a HDRI file by combining different exposures.
I have applied the HDRI pano to a vray light dome

This is where I go wrong……..

I now need to align the HDRI pano with the in situ photo, to do this I need to rotate the HDRI map until for example the houses are on the left and the trees are on the right as per the in situ photo.
But in order to see this I have placed the HDRI pano as a viewport background so that when I rotate the HDRI pano in the material editor it updates in the viewport so I can see if it has aligned correctly.
But because the HDRI pano does not fit within the viewport ie clipped, not mapped correctly whatever, it’s hard to determine if it is at the correct horizontal rotation.

One I have got the correct rotation I will remove the HDRI pano from the viewport background as it is only needed in the vray light dome, it’s purely in the background to try and get it aligned.

I am not trying to map the HDRI pano in my scene and use it as a background, so mapping it to a cylinder and adding a vray light material doesnt help me. I am trying to align and get the correct horizontal rotation in relation to where I was standing when I took both the in situ and HDRI pano.
Hope that clears up what I am trying to achieve, sorry I thought it was a common problem trying to align pano images for IBL in situ.

[Guest]

Here is a render i did without any reflection or materials after i camera matched the photo. I expected the HDRI pano when added to the viewport to closely but not exactly match the in situ photo so I can check alignment but it doesnt, instead it appears as the first image in my first post.

I now need to add the HDRI pano using image based lighting via the vray light dome. But in order to get the correct position of the sun and reflections it must be correctly aligned.

[joconnell]

It is a bit of a pain in the arse to align them alright but in a lot of cases the panoramas are true spherical images whereas yours in this case seems like it's missing the top (sky) and bottom (ground under your feet) images so where you use it as a viewport background it's being stretched vertically, hence people saying you've got more of a cylinder than a sphere. It looks like you stood in the same spot and turned around horizontally taking images by hand (Can't see a tripod in your shadow on the bottom left driveway section )

To get your background in place, you'll have to make some simple geometry for the house walls and drive way, then make a camera that matches your rough geometry up with the lines of the house walls in the background and camera project your house photo to this geometry. Your best bet is to make your render res the same width and height ratio as the background image you took to make it easier to get a camera angle that works. Now when you put your car model in, it'll be able to reflect the walls of the house and drive way properly. Next map your image inside a cylinder since it seems to fit the way you've shot the image more than a sphere - you'd put this surrounding your scene with a light material as your actual source of lighting - you can make this invisible to the camera so it's not appearing as a background for your car, it's only there for lighting. If you want to go for a vray light with a map instead, I find it quite handy to put a sphere in the middle of your scene, give it a 100% reflective material and then you can adjust the rotation of the map in your vray light by 30 degree increments using the reflective ball as a guide until it's correct.

[stef.thomas]

Ok, sorry I misunderstood somewhat, looks like you are on the right track. The HDRI and your background image aren't going to line up with each other in the viewport as they were taken from different spots. In order to align it correctly I would get a position in your viewport looking over your car and down the driveway. Then rotate your HDRI till you are looking down the driveway with the sun positioned just to the left. If you need to see more then use the field of view tool to widen your viewport perspective. There will also be some distortion due to the fact that you are applying a cylindrical image to a dome, but there's no way around that in this case.

[joconnell]

It'd be worth playing with the v tiling of the image you're using for the hdri to try and squeeze your image into the correct place. If you think of a sphere as being a top third, middle third and bottom third, the panorama you've shot is mainly covering the middle third. If you set your tiling of your image to something more than 1.0, it'll start to squeeze your panorama vertically down into the middle third of the dome and get more correct. Turn off the tiling of the map vertically and see how it looks - you might need to set a colour value for the vray light to fill in the areas of the light dome that are being revealed by the squeezed mapping.

[Guest]

Ok I think I get it… Because my map is not a true spherical pano it won’t align correctly in my viewport.

@ stef.thomas, “Then rotate your HDRI till you are looking down the driveway with the sun positioned just to the left” That’s what I tried to do and the first image in my first post is what I get.

@ joconnell, nice idea with the modelling of the surroundings but I was hoping to come up with a solution just using a vray dome light and IBL. But I will try tiling it to see if it helps thanks!

[joconnell]

Sorry, I was looking at your first image (the viewport capture) as being the angle you wanted to render in terms of modelling bits to project on - you popped up the clay render test while I was typing - I must reply faster in future instead of pondering

What stef is saying about rotating the hdri is to get it in roughly the correct place. The image you've taken will never match up in your viewport since you've got photos of a street that had a distinct ground, walls and a sky so there's lots of different planes of geometry. This is being mapped into a very simple sphere which is a really inaccurate representation of what the scene you shot actually was. The next issue is the camera you're viewing your environment background is totally different from what you shot the scene with - you'd really want to be viewing the scene through a spherical camera so that you get a similar level of warp to what's on the background.

In this case you're expecting something a bit more exact while using really inaccurate methods - a hdri dome image is a representation of the lighting in a scene but not a 100% accurate one from a direction point of view. Thing is it's definitely far better looking than any other method we have to use. In this case I'd only worry about getting the rough direction of the lighting correct and that'll be close enough. If you want more accurate lighting and reflections, you'd make your scene in a slightly different way you'd make simple shapes for the street and project your hdris on to those. If you take for example the side panels of the car, the reflection rays they shoot out would then hit off the correct bit of wall or ground that they would have seen in real life, rather than an incorrect part. At the very minimum you'd want to use a ground plane so that any part of the car that'll be very close to it will reflect correctly. Everything else can be good "enough" and it'll look correct - for example ILM had about 10 reflection maps they'd use regularly for the first 10 years they were doing cg and they worked a treat

[Guest]

The plan was to come with a cost effective and simple way of creating HDRI images for IBL, I work mainly within retail and I create a lot of retail interiors. I always carry my iphone when on site and clients love in situ shots, that look realistic. So I have been doing some testing and trying to come up with a way of doing all this without the need for a tripod, SLR etc.

My pit fall is the creation of the spherical pano, which after testing and speaking to you guys is what is required to match the viewport correctly. So I have found this http://www.pixeet.com/ Going to order it and give it a go.

At the moment the HDRI pano that I have shown you, when reflecting on the car is very distorted due to it not being a proper spherical image. I will post a render up soon to show you the result.

[stef.thomas]

The quality actually looks pretty impressive from that lens! How would you handle the exposure bracketing though?