understanding Irradiance Map

[bluediablito]

understanding vray Irradiance Map

sorry to bother any one but i am a little confuse on vray Irradiance Map

(my uncle is Italian and bought the vray book with the dvd. He finish reading it and has given it to me to read so i can better understand vray, but my Italian is not as good as his.to fully understand the book i have use Google translator but it some times it does not make any sense)

so here is my understanding..............

 

when it comes to Irradiance Map a resolution of 1280x960 at a Irradiance Map of min rate=-4 and a max rate=-1 is broken down to 4 prepasses

the resolution is divided by 2/2/2 because of the -3 (-3 makes 2^3=8)and 2 because of the -1 (-1 makes 2^1=2)

 

4 prepasses

1280 x 960 / 2 = 640 x 480 4th prepass

640 x 480 / 2 = 320 x 240 3rd prepass

320 x 240 / 2 = 160 x 120 2nd prepass

160 x 120 / 2 = 80 x 60 1st prepass

 

this is my normal rendering resolution

max rate=0 min rate=-4

1200 x 675 /1 = 1200 x 675 5th prepass

1200 x 675 /2 = 600 x 337.5 4th

600 x 337.5 /2 = 300 x 168.75 3rd

300 x 168.7 /2 = 150 x 84.375 2nd

150 x 84.37 /2 = 75 x 42.187 1st

 

now my questions are;

1. would it be a smart idea to have the final prepass pass at the same resolution as the original one, or is there any way to have a higher resolution on the prepass than the original resolution?

2. How would i calculate a positive number? (ex...max rate 1 and min rate 8)

3.would it be a good idea to have more prepass to achieve a higher resolution?

 

if any one can explain Irradiance Map a little better for me i would appreciate it

 

thank you in advance

please note that i have started to read the book and i am in the first few chapters.

Edited January 15, 2010 by bluediablito