daveb867

Hi guys another query that i hope people can help with

i have a fairly decent light setup for an exterior that i am practising with

however, i want to keep this light solution but use a sky bitmap in the background so i have clouds etc.

the scene is setup with a daylight system mrsun mrsky mrphysicalsky photgraphic exposure

i believe you can place bitmaps in the haze slot of the mrphysical sky but this doesn't seem to work

i have attached the original render and below is a link to the sky texture i am using

http://mpan3.homeip.net/content/reso...ky/dayfair.jpg

Attached Images

exterior.jpg (13.2 KB, 75 views)

MasterZap

If you want to put the sky bitmap in the haze slot, read this. You need to turn it's output up to around 10-ish.

If you just want to use it as an actual background image, well, then just use it as a normal spherical environment in the environment map (remove the physical sky completely), or, if you only want it as a background image, use it in the "background" slot of the physical sky itself. Either way, you should also read this to understand that you need to turn it's output level up approximately 2500,0

/Z

__________________
mentalraytips.blogspot.com - mr Zap Andersson - a completely mental shader guy

fco3d

puting a sky image with the Mr Combo sun and sky it is a very pain in the but, but there is some work around, normally I put the sky in post but if you want an animation I rather put a dome sky and make a work around that Jeff Patton explain here.
If you still want to use the image map in the mrsky you have to pull way up the RBG values of the image, remember that Mr Sun and sky use "a lot" of illumination and with the photographic exposure it is more evident, so your image must have the same "output" values

fco3d

LOL right after I did my post I saw yours, and I was reading your black rendering problems in your page !!!
glade to see you around here Master!!

daveb867

ok in the image i posted i had the settings as described, i then made one change and that was putting the bitmap in the haze slot, i sat the haze value to 1 and the output level on the bitmap to 10, the bitmap was only just visible but it was also not projecting the true colours it did when viewed in a normal windows picture viewer????

i then tried with a skydome and just a mrsun, everything works but i had to select unitless on the photgraphic exposure and up the value of that otherwise the scene rendered black, and also the mrsun was having no effect even tho i had used ray switchers on the mental ray material etc, with me selecting unitless on the exposure control would i then need to up the intensity of the mrsun to get it to have an impact on the scene?

thanks for the help so far guys

daveb867

also i am having difficulty getting my head around altering the settings of the daylight system so that the sun intensity, position etc matches that of the sky bitmap, if i use a sunset bitmap, would i need to reduce intensity (mulitplier) of sun and sky and obviously the time, and would i need to alter exposure control settings to accommodate

how do you guys go about this??

eventually i want to render out various images of the same building at different times of the day but i want to use sky images as the sky rather than the physical sky. i also want it to look as photorealistic as possible.

what are your general workflows for this kind of process?

daveb867

any more follow ups on this guys??? struggling quite badly

really want my renders top notch so all the help is much appreciated

MasterZap

Of course not; the whole point of the "haze" method is to simply use some *picture* of clouds to drive the haze. The only thing used is the shape of the clouds (derived from the brightness levels of your photo - you may need to play with contrast in some cases). The colors come from the physical sky simulation that uses different haze values for different directions in the sky, hence generating a "faux claud" result.

It's not true volumetrics, of course, but it's pretty nice because it follows the color over time-of-day, and gives you the visible sun disk for free.

I never said to use just the mr sun. You should still use the mr sun and mr sky lights, only you replace the environment shader with your sky image. So only the "visible" component of your sky is swapped out for your photograph.

Why would you use ray switchers in this case!?!

You have two options with a "sky background photo"

a) Keep using the mr Sky as lightsource
OR
b) Use the "Skylight" as sky lightsource, set to "Use scene environment" mode, multipleir 1.0

In either case you must make sure the physical intensity of your "background photo" matches that of a sky, which you by turning up your sky bitmap's "Ouput Level" - or - as you tried - by playing with the "physical scale".

My blog is shock-full of explanations on this topic.

Unitless/Physical mode only impacts "non physical" things (in a practical sense), i.e. whatever this is set to, doesn't impact the suns contribution, because the sun has a fixed physical interpretation at all times, and the exposure control treats those physical values with the physical exposures at all times. The unitless/physical switch is for any non-physical properties, like non-photometric lights, and, also, including your "background image".

/Z

__________________
mentalraytips.blogspot.com - mr Zap Andersson - a completely mental shader guy

MasterZap

That's why the easiest way to achieve this is through the "haze trick". Yes, you do not get "perfect" clouds (nothing volumetric or thick), but a very nice "faux cloud" look, and it follows your time of day automatically and gives you a sun disk for free.

Also, by the way, I just attended a lecture by an architectural photographer. They say they avoid clouds at all cost, and if one sneaks into an image, they paint it out in photshop...

Ain't the world fun?

/Z

__________________
mentalraytips.blogspot.com - mr Zap Andersson - a completely mental shader guy

daveb867

thanks a lot for your help zap

when i mentioned using a rayswitcher on the skydome, i was following a workaround described by jeff patton, where he talks about applying a bitmap to half a sphere that encloses the scene. it can be found on his blog.

i eventually got it to work

all i was worried about was trying to match the daylight system to that of the different bitmaps i had for different times of the day.

but with your help i am nearly there.

i am also looking for a best practice when it comes to gamma settings for p/graphic exposure and whether they should be changed when using logarithmic exposure.

the reason for this is that when i do make a render using a sky bitmap, the colour of the bitmap in the render is not the same as the original bitmap file?????