matching photos and rendering via HDRI

[gustojunk]

Hi All,

I need to make some renderings of a car interior, the dashboard area. I'm designing a product that goes on the center panel. So I want to take some pictures of a car, render the model of my design in Vray and match the background image with the foreground rendering. I will be shooting like 4-5 different angles for my renderings backgrounds and I'll match them to camera views in Max.

To match lighting I want to make a custom HDRI Image. I have access to a Nikon Coolpix 5700, and a wide angle lens for it if need it.

I've found some tuts about making HDRIs with HDRshop. I get the concept but I have a couple of questions:

do I use A) wide angle lens or B) chrome ball?

If I use A (wide angle lens) where in the interior of the car do I place the camera? one shot or 2 shots?

If I use B (mirrored chrome ball) where Do I place the Chrome Ball? and from where do I shoot the picture?

For all my views the center of the composition will be the central part of the angles and the photos for the background will be shot from the driver's viewpoint, passenger's viewpoint, center of back seat, from the outside or the passenger's window. etc.

I'd really appreciate any feedback on this

Best Regards,

Gustavo

[J_Bug]

Easiest way would be to use the chrome ball and place it about where the object will be rendered. It doesn’t have to be exact in most cases. If the object you're designing has highly reflective/ refractive materials then you'll probably want two HDRIs. The first should be very high res and is used in the Environment override Reflection/Refraction slot. The other can be a lower resolution HDRI for the GI.

For the background plate...
Since it attaches to the dashboard you might want to take some measurements of the dash etc. so that you can match matte objects for the shadow casting. Distance from the camera of the CG object could help in matching likewise.

Will it be an animation on a video plate in the end or is this just for a still?

--Jon

[gustojunk]

thanks for your reply J-Bug.

Mmm, I didn't think about measuring the distance from camera to CG object in each view, I was planning to match view just with plotted known points, but this will help a lot!

The CG object will not protrude from the car panels, it's more like replacing a part by another, so I will not need matte shadows objects in this case.

I'm plannning to do just a few high rez stills, no video. This will be my first project of matching real and CG stuff, I might go to video the next time around though I rather do baby steps first.

One more question for you: what are the advantages of usinng a lower rez. map for the lighting? Does it render faster? how much faster?

Regards,

Gustavo

[J_Bug]

Just to save on memory at render time.

What type of material is your object made of?

--Jon

[J_Bug]

These links get down to what quality you really need.

http://www.andrew-whitehurst.net/hdri_tut.html

http://www.cgtechniques.com/tutorials/synthhdr.php

--Jon

[gustojunk]

Hi Jon,

I read your links, thanks, it really helps. I also went to the hdrshop forums and I found a bunch of stuff there too, I even saw a lot of familiar names there too

I ordered a 3" ball bearing chromed steel ball today. I'd should be here in a couple of days. BTW I got it from http://www.salemball.com, $71.80 plus shipping for those who might want one.

For the actual HDR I'm going to go the shutter speed way versus changing aperture. So my depth of field and other values don't change. Now how many shots are too many? or the more the better?

It looks like I can do 30 sec. all the way to 1/4000, or even 1/8000 if I use another Nikon camera we have. That means 18-19 shots!!! I read somewhere (don't ask me where, it's been a loong night of surfing) that I should do about 12 shots.

Also I have used in the past really poor quality HDRs I downloaded from the web and somebody pointed out it was because they were done with too few exposures. Therefore the quality of shadows was very poor. But my question is, would too many ruin my HDRI too? Like make it too bright or something?

One more question, it might sound stupid but I'm kind of clueless about photography: Since I only change shutter speed, the other settings just stay put, but what F-stop and ISO settings do I shoot at? this will be done during daylight, outdoors, from inside the car.

Gustavo

[J_Bug]

Shutter speed looked to be the best way for me also. Your depth of field will be important in a car but I'm thinking maybe not so much for the HDRI.

The aperture should be set for the sunny day. Your safest bet should be 8 or 5.6 I think. 12 shots sounds perfect if you can get that many. Seems like most people try to get anywhere from six to eighteen shots I've noticed. My last set that our cameraman took for a short I'm working on was a total of seven for each HDRI.

Ok... I took photography back in high school so let me try to get this correct (a little research to verify what I'm saying wouldn't hurt )...

The ISO can be almost anything on a nice sunny day but if your windows are tinted then you may want to take this into consideration. Just remember that the higher speed film, the grainier the image will be. If your taking a 35mm photo but you want it to be print in a magazine then 400 would be way too grainy when enlarged. I'm guessing you'll use the same role of film for the background plate. One other thing I'd suggest is to buy a few car sun reflectors to use as bounce surfaces to get the sun where you want it. On a sunny day under certain window tints the shadows are harsh in a car. If you don't regularly take many photos you may want to research a term called "the golden hour"...

http://pages.prodigy.net/pam.orman/j...030322_25.html

but you can get around this with proper light translation.

Have fun setting up the camera in your car. Be careful not to jolt the tripod. Better yet you should invest in a clamp of some kind ...

http://shop.store.yahoo.com/cinemasu...uccupmoun.html

Good luck,
--Jon