Rendering Parameters: What are they and what do they do

The table below gives useful ranges for some parameters.
The "min" value gives the fastest, crudest rendering. It is not necessarily the smallest value numerically.
The "fast" value gives a reasonably fast rendering.
The "accur" value gives a reasonably accurate rendering.
The "max" value gives the ultimate in accuracy.

Param	Description	Min	Fast	Accur	Max	Notes
-ps	pixel sampling rate	16	8	4	1
-pt	sampling threshold	1	0.15	0.05	0
-pj	anti-aliasing jitter	0	0.6	0.9	1	A
-dj	source jitter	0	0	0.7	1	B
-ds	source substructuring	0	0.5	0.15	0.02
-dt	direct thresholding	1	0.5	0.05	0	C
-dc	direct certainty	0	0.25	0.5	1
-dr	direct relays	0	1	3	6
-dp	direct-pretest density	32	64	512	0	C
-sj	specular jitter	0	0.3	0.7	1	A
-st	specular threshold	1	0.85	0.15	0	C
-ab	ambient bounces	0	0	2	8
-aa	ambient accuracy	0.5	0.2	0.15	0	C
-ar	ambient resolution	8	32	128	0	C
-ad	ambient divisions	0	32	512	4096
-as	ambient super-samples	0	32	256	1024
-lr	limit reflection	0	4	8	16
-lw	limit weight	0.05	0.01	0.002	0	C

NOTES:

A)    This option does not affect the rendering time
B)    This option adversely affects image sampling (ie. use -ps 1)
C)    Maximum value disables optimization and can be very expensive

ARTIFACTS ASSOCIATED WITH OPTIONS

Param	Artifact	Solution
-ps	missing pieces to objects	decrease value by 50%
-pt	some soft edges are very jagged	decrease value by 50%
-pj	diagonal edges are like staircases	increase value to 0.9
-pj	edges look too erratic	decrease value to 0.4
-dj	shadows are unnaturally sharp	increase value to 0.7
-ds	large sources cast unnatural shadows	decrease value by 50%
-dt	some shadows disappear	decrease value by 50%
-dc	inaccurate values with many sources	increase value to .75
-dr	missing multiple mirror reflections	increment value
-dp	incorrect mirror reflections	double value
-sj	specular reflections too fuzzy	decrease value to 0.2
-sj	specular reflections too sharp	increase value to 1
-st	some specular highlights missing	decrease value to 0.02
-ab	lighting in shadows too flat	increment value
-av	overall light level seems too high/low	decrease/increase value
-aa	uneven shading boundaries in shadows	decrease value by 25%
-ar	shading wrong in some areas	double or quadruple value
-ad	splotches of light	double value
-as	splotches of light	increase to half of -ad setting
-lr	some multiple specular reflections gone	increment value
-lw	some specular reflections gone	decrease value by 50%

TIMINGS ASSOCIATED WITH OPTIONS

Param	Effect on Execution Time
-ps	inverse, halving value increases rendering time up to four times
-pt	minor, decreasing value causes modest increase in rendering time
-pj	no effect
-dj	indirect, increasing value requires -ps parameter to be reduced
-ds	inverse, halving value causes rendering time to approximately double
-dt	inverse, halving value causes rendering time to increase about 50%
-dc	direct, affects rendering time up to 50% over its 0 to 1 range
-dr	direct, depending on the scene each new reflection can double time
-dp	minor,affects start-up time only, higher values take longer
-sj	no effect
-st	minor, a value of zero may increase rendering by 50% over maximum of 1
-ab	direct,doubling this value can double rendering time
-aa	direct,doubling this value approximately quadruples rendering time
-ar	direct,effect depends on scene, can quadruple time for double value
-ad	direct,doubling value may double rendering time-as direct, effectively adds to
-ad	parameter and its cost
-lr	minor, increase causes very slightly longer rendering time
-lw	minor, decrease causes very slightly longer rendering time