What is occlusion and baking?

[thatoneguy]

You might have a more challenging time doing this on the cheap then you did a month ago. But Target had these gigantic chrome christmas balls for 2 dollars each.

Radiance maps give you the ability to perfeclty match the light as it is in a real environment. You get all of the bounces, all of the diffuse lighting, everything out of the photo. The drawback is, it works best for outdoor open scenes, and objects sitting inside of a room with a photographic background. It doesn't work for lighting, say a Bedroom, unless the HDRI light is outside shining in through a window, what I'm saying is, you can't take an HDRI probe of your bedroom and then light another room with the same lighting, that just wouldn't make any sense. It only functions as a dome light.

Anyway how to do it?

Buy a garden steel gazing ball/globe

http://www.hdrshop.com/

Go here and follow the tutorials on the page.


Occlusion baking is a way to fake the nice diffuse shadows that tend to exist on a cloudy day or in the real world, without actually having to run a GI calculation. In short it takes a sample of each point on your mesh and then calculates how much of the world that point can see. The more it can see the brighter it gets, think shadows in cracks. You bake this onto your model so that as I said before, it looks like it was rendered with GI, you can then use normal ray traced lighting/shadow maps to light the scene.

[kungfuelmosan]

kool thanks - i know a bit about HDR images - what i meant is whats the point in shooting multiple shots at different exposures and blending them together - why cant you jst take one photo and can you use LDR image for a radiance map - also when i said to light a room i worded it wrong - i meant how do you take an HDR image of a room and use windows and stuff in the room to light something inside a room not to lght a room - if that makes sense - and can you buy a special steel/chrome ball or something made for taking light probe images from anywhere and what are they called?

also i didnt just mean occlusion baking - what is any type of baking - like right clik > materials > new bake set? - and are there any tutorials or maya documentation on baking (occlusion etc) i also read a tutorial in the gnomon workshop aout baking a material or something onto an object that emits particles and the praticles inherit the color where they come from - or something like that - what is this?

[kungfuelmosan]

i need to think before i type!

[thatoneguy]

Hmm... not sure what that baking is specifically.

The reason you shouldn't (not can't) use a low Dynamic Range image is because you only have values between 0 and 255.

An example.

You take a photo of a sheet of paper. It is white. The photo is slightly overexposed for the paper and as such, the image is white. You can't go beyond white. White is white. But in the real world white isn't white. I'm sure you won't argue that a white sheet of paper is darker than the nice big white day star hanging over our heads for a good part of the day.

The light in the world around you is logrithmic, what your eyes see as 25% gray and 50% gray aren't 100% different, they're actually hundreds of times brighter. HDRI images take a number of photos and compare the pixels at known exposure levels and then can extrapolate what the true relative brightness of each pixel is.

[kungfuelmosan]

ok cool - so can you do hdr with a stock standar fairly good digital camera and a steel ball?

also does a straight out hdr image need to be altered or can it be used as is for a radiance map in maya - so like can i get a hdr image and use that for IBl or does it need to have something done to it

and does a hdr image light a scene in maya by itself?

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