this shader is based on the Siggraph paper by Greg Spencer et al entitled

"Physically Based Glare Effects for Digital Images"

 

how does it work?

glimmer is a mental ray output shader - i.e. it is a post rendering process

each pixel in the image is scanned and if it is above a user-defined level of brightness the glimmer effect is triggered - called a 'peak'

the glimmer effect constitues optional flares(blooms), lenticular halos(rainbow effects) and cilliary coronas (streaks eminating from the centre of the 'peak')

glimmer can be computationally very heavy - every pixel has the potential to influence every other pixel,
i.e. on a PAL picture there is the potential for 171,992,678,400 calls to determine the relevant glimmer effect

every effort has been made to speed up this process without negating the visual effect
indeed Peter Hardie was using glimmer on 5000 frame sequences without problem(see below)

 

important information!

1> the lower the glimmer threshold the greater the amount of 'peaks' you are asking glimmer to make

more 'peaks' equates to more computations so try to keep the threshold high (1,1,1) and work your way down

 

2> use the 'peak controlled intensity' option combined with smaller test renders to tweak parameters

smaller resolutions generate less 'peaks' and are thus quicker

changing the resolution will produce differing results but the above option helps to reduce this to a minimum

 

3> use 'progress report' in the xsi rendering options under logged messages to see glimmer's runtime stats

it will tell you information about the amount of peaks and the current vertical pixel line being processed

if you deactivate glimmer in the glimmer parameter box, glimmer will still determine how many peaks there are in the image
and inform you via the runtime stats thus allowing you to gauge potential render times

 

4> To be sure the trigger color threshold is high enough, use a color picker in xsi and pick a bright color from a render region

monitor colors are deceptively low and you may find guessing thresholds inaccurate

 

installation

 

1> download glimmer

right click on the link below to save the addon

WIN 32 XSI Version 4.0 XSIADDON

2> installing in XSI

you can either drag and drop the addon into xsi

 

3> inside XSI

open pass>edit>current pass

go to the ouput shader tab

select 'add'

browse to the glimmer addon path

select glimmer

 

4> glimmer properties

 

Activation Enable: Enable the glimmer effect Threshold: Specify the pixel color to ativate glimmer Independant Color Channels apply glimmer on a per channel basis rather than uniformly Camera: Field of View:Affects the size of the glimmer Flare Functions: Enable:Turns on the flare-like bloom effect Flare 1 to 3 :These are 3 different kinds of flare, 1 is the smallest and 3 is the largest. These values should sum to 1 for a realistic effect. Flare 1 to 3 Intensity:Used to control the overall flare brightness. Lenticular Halo: Enable:Turn on the halo/rainbow effect. Intensity:Controls the halo's brightness. Light Wavelength Controls: Scatter:Used to augment the light wavelengths. Red, Green and Blue: The wavelength of the appropriate color channels (nm) Ciliary Corona: Enable:Turn on the streaking corona effect. Threshold:controls the amount of streaking. 0 represents no streaking, 1 total streaking. Strength: Blends the intensity of the streaking(fades it out). Random Seed: Enable:Turn on the user defined random seed. Seed:The seed number to use. Peak Controlled Intensity: Enable: Augments the brightness of glimmer by the amount of peaks. Because changing the resolution of an image can drastically change the brightness of glimmer, this options helps to maintain a certain amount of control when working in differing resolutions - e.g. smaller test renders.

 

history

glimmer version was generated for Peter Hardie and his studies of 'Light on Water'

this collection of still and moving imagery was exhibited at Siggraph 2003

please visit http://www.virtualreflections.com/ for more information about his work