"...Mitchell filtering, which in most setups needs higher radii to
create nice-looking imagary, many more samples are taken into
consideration for a single pixel's colour value...."
indeed you did...
On 6/5/06, *André Adam* <a_adam(at)49games.de <mailto:a_adam(at)49games.de>>
wrote:
"filtering doesn't decide how many samples are taken..."
Hey Steven, that's exactly what I've said, reread my mails.
However, the
filter size *does* decide on how many samples will be combined for a
single pixel *after* all rays are shot by creating an ellipse
around the
center of that pixel and collecting all the samples within the
given x/y
radii.
Your observations regarding the eye-rays are interesting, though. We
seem to have a few extra rays in there, but I see the basic idea of
samples = pixels with a sampling value of 0 still being valid,
don't you
think? At least I can live with a variance of less than ten
percent... ;)
Steven Caron wrote:
> /deep breath!
>
> /filtering doesn't decide how many samples are taken...
>
>
file:///C:/Softimage/XSI_5.0/Doc/mental_ray/manual/node76.html#INDEX188
>
> "...The *filter* statement specifies how multiple samples are to be
> combined into a single pixel value..."
>
> and if you just take look at jitter thats only two definitions down
> from filter...
>
> "...Without *jittering*, samples are taken at the corners of
pixels or
> subpixels..."
>
> and if you turn jitter on. with AA min 0 and max 0... mental ray
> kindly turns jitter off :) why? Because it will introduce artifacts
> with that low of a sampling rate...
>
> //INFO : RC 0.2 warn 082008: jittering disabled because max
> samples < 1
>
> So according to you a 100 x 100 render would produce 10000
samples? (
> eye rays ) Lets test this!
>
> I setup a format of... 100 x 100. AA min of 0 and max of 0. Jitter
> OFF. Threshold rgba to 1.0 and filter type box 1 1, but threshold
> doesn't matter because of min and max samples being the same and
> filter doesn't matter because it only averages samples already
taken.
>
> turn progress on...
> //INFO : RC 0.2 info : rendering statistics
> //INFO : RC 0.2 info : type number per
> eye ray
> //INFO : RC 0.2 info : eye rays
> 10816 1.00
>
> hmmm interesting!
>
> I am going to throw another variable in here... task size or tile
> size. this option will really increase or decrease your samples...
> smaller task size is going to give you more samples.. larger is
going
> to give you less. Here is a quick formula for predicting samples. I
> say predicting, because there is no way to know everything they are
> doing internally, short of being a mental images developer.
>
> task size + 1 * task size + 1 = samples per tile...
>
> To test this make a 32 x 32 resolution AA min 0 max 0 and turn your
> "tile size" to 32x32. You can leave automatic in cause most likely
> mental ray will choose this, but just in case force it. you know so
> you feel like your in control. You will get...
>
> 32 + 1 * 32 + 1 = 1089
>
> have fun.. do some more tests...
>
> André Adam wrote:
>
>> To add to this, the position sampled is only important for the
>> filtering algorithm that collects samples using a specific radius
>> around the center of the pixel. With an aa setting of 0 and a box
>> filter with a size of 1, indeed four samples will be considered to
>> retrieve the final colour value for this pixel. However, hardly
>> anyone uses a box 1/1 filter. When switching to the more popular
>> Mitchell filtering, which in most setups needs higher radii to
create
>> nice-looking imagary, many more samples are taken into
consideration
>> for a single pixel's colour value. However, the sample density shot
>> by the renderer *does not* increase in this scenario, with aa 0 it
>> stays one sample shot per pixel.
>>
>>
>> André Adam wrote:
>>
>>> Nope, with aa 0 you get exactly as many samples as you have pixels
>>> for the whole image. It definately is one sample per pixel. Not
>>> centered, but that doesn't make much of a difference, the spacing
>>> between the samples stays one pixel regardless of the position
>>> sampled. It's just about offsetting the sampling raster. Which btw
>>> gets randomised anyways when enabling the sample jitter option.
>>>
>>> Cheers!
>>>
>>> -André
>>>
>>>
>>> Steven Caron wrote:
>>>
>>>> "...and one sample per pixel (aa setting 0)..."
>>>>
>>>> just like bernard and kim said about threshold being
misunderstood
>>>> this too is misunderstood.
>>>>
>>>> mental ray samples at the corners of a pixel. meaning 4 per
pixel
>>>> not 1. but not always 4 new samples because mental ray can share
>>>> samples with bordering pixels.
>>>>
>>>> *bracing myself now*
>>>>
>>>> steven
>>>>
>>>> On 6/2/06, *André Adam* <a_adam(at)49games.de
<mailto:a_adam(at)49games.de>
>>>> <mailto:a_adam(at)49games.de <mailto:a_adam(at)49games.de>>> wrote:
>>>>
>>>> A really nice example covering this problem is a
hemisphere mapped
>>>> with
>>>> a clear night sky showing lots of small stars. If the min aa
>>>> setting is
>>>> too broad (and one sample per pixel (aa setting 0) might very
>>>> well be
>>>> too broad), the rays will likely completely miss out certain
>>>> stars on
>>>> certain frames which leads to the stars wildly flickering in
>>>> animation...
>>>>
>>>>
>>>> kim aldis wrote:
>>>>
>>>> >I'm not trying to put you down here Bernard but there are
>>>> situations where
>>>> >settings like this aren't good and you should have some
idea of
>>>> what sort of
>>>> >image you're rendering before making decisions about aa
settings.
>>>> In some
>>>> >shots, messing with threshold won't make any difference
at all,
>>>> raising max
>>>> >settings will make little difference unless you bring up
the min
>>>> settings.
>>>> >You're right, threshold is largely misunderstood. Let's
try and
>>>> shed some
>>>> >light:-
>>>> >
>>>> >here's something you can try. Get a cube, unit 1. scale
it so
>>>> it's really
>>>> >long and really thin - 0.02, 0.02, 35.
>>>> >now duplicate it 20 or 30 times and space each cube one unit
>>>> apart in x. Now
>>>> >shift them all back away from the camera so you get a good
>>>> convergance. Lots
>>>> >of thin, parallel lines in the distance, all converging
to the
>>>> vanishing
>>>> >point is what you're looking for.
>>>> >
>>>> >Now mess with the aa settings and pay close attention to the
>>>> quality where
>>>> >the cubes are nearly converging. Try 0,3 and mess with the
>>>> threshold. Not a
>>>> >lot of difference, is there, even if you set the
threshold really
>>>> as low as
>>>> >you can get it. In fact, changing the threshold varies
not a lot
>>>> at all.
>>>> >
>>>> >now compare 0,2 with 0,3. Not much better. And I'll bet
if you
>>>> try 1,2 it'll
>>>> >be way better than 0,3. Again, regardless of the threshold.
>>>> >
>>>> >The point here is that there's a real danger of getting
it wrong
>>>> if you
>>>> >start generalising aa settings and don't take into
account the
>>>> kind of image
>>>> >you're rendering, as Helen is finding out, since
sampling grain
>>>> is fine
>>>> >detail. I just tried something here. Pushing aliaising
to 1,2
>>>> with default
>>>> >threshold gave me better improvement than doubling the
>>>> sampling size.
>>>> >lowering the threshold improved things a bit but nothing
worked
>>>> better - nor
>>>> >was faster - than raising the min setting, bringing it
closer to
>>>> the max.
>>>> >
>>>> >If you really want to see how well - or otherwise - aa is
>>>> working, turn on
>>>> >'view sampling' in the region diagnostic tab. It's most
>>>> revealing.
>>>> >
>>>> >-----Original Message-----
>>>> >From: owner-xsi(at)Softimage.COM
<mailto:owner-xsi(at)Softimage.COM> <mailto:owner-xsi(at)Softimage.COM
<mailto:owner-xsi(at)Softimage.COM>>
>>>> [mailto: owner-xsi(at)Softimage.COM
<mailto:owner-xsi(at)Softimage.COM> <mailto:owner-xsi(at)Softimage.COM
<mailto:owner-xsi(at)Softimage.COM>>]
>>>> On Behalf Of
>>>> >Bernard Lebel
>>>> >Sent: 01 June 2006 16:23
>>>> >To: XSI(at)Softimage.COM <mailto:XSI(at)Softimage.COM>
<mailto:XSI(at)Softimage.COM <mailto:XSI(at)Softimage.COM>>
>>>> >Subject: Re: shadow flicker
>>>> >
>>>> >I would definitely use a min of 0 and a max of 3.
>>>> >
>>>> >Also, what is generally ignored or misunderstood is the
treshold.
>>>> The
>>>> >treshold color is a control for how sampling is done. Lower
>>>> values means
>>>> >that sampling occurs with lower contrasts, in other
words, the
>>>> level of
>>>> >sampling have more chances of getting closer to the max
value.
>>>> Higher
>>>> >treshold means a higher contrasts is tolerated before
requiring
>>>> another
>>>> >level of sampling, so less samples may be takne.
>>>> >
>>>> >I never work with treshold higher than 0.05, and had to
go as
>>>> low as
>>>> >0.005 on few occasions. Note that at that point, if the
image is
>>>> detailed,
>>>> >you should consider ignoring adaptive sampling
altogether and use
>>>> same min
>>>> >and max values. If the image has significant amounts of
constant
>>>> colors
>>>> >(like shadow passes, black backgrounds in the likes), then
>>>> adapative
>>>> >sampling is still a viable solution.
>>>> >
>>>> >
>>>> >Lastly, my rule of thumb for the filtering is Gaussian
3/3 for TV
>>>> output and
>>>> >Mitchell 4/4 for film output. Gaussian gives a blurrier
sample
>>>> >interpolation, which may "conceal" minor imperfections.
>>>> >
>>>> >
>>>> >
>>>> >Cheers
>>>> >Bernard
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >On 6/1/06, Helen Bucknall <helen(at)helenbucknall.com
<mailto:helen(at)helenbucknall.com>
>>>> <mailto: helen(at)helenbucknall.com
<mailto:helen(at)helenbucknall.com>>> wrote:
>>>> >
>>>> >
>>>> >>Mostly I just use min -1 and max 2. and box filtering 1 or
>>>> sometimes I
>>>> >>use triangle 2 for a softer effect.
>>>> >>
>>>> >>I output a string of 852 x 480 bmps to my clients and then
>>>> they mpeg
>>>> >>it somehow and wack it up on big plasma screens. They never
>>>> complain.
>>>> >>When they want stills for print I just render a frame
out huge
>>>> >>(3000+)but leave the antialiasing the same.
>>>> >>If it's for telly I do HD res. If it's to be comped
with live
>>>> action I
>>>> >>ask what anti aliasing they want.
>>>> >>
>>>> >>
>>>> >>
>>>> >>Bernard Lebel wrote:
>>>> >>
>>>> >>
>>>> >>
>>>> >>>Samples 20 is a bit low. I generally put 64 as soon as
I set
>>>> up the
>>>> >>>shadow map.
>>>> >>>
>>>> >>>What do you mean with "standard antialiasing"?
>>>> >>>
>>>> >>>
>>>> >>>Bernard
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>On 5/31/06, Helen Bucknall <helen(at)helenbucknall.com
<mailto:helen(at)helenbucknall.com>
>>>> <mailto:helen(at)helenbucknall.com
<mailto:helen(at)helenbucknall.com>>> wrote:
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>>>OK. I dragged the spotlight in closer to the scene
elements
>>>> and it
>>>> >>>>seems to have stopped all the flickering! It wasn't
that far
>>>> away,
>>>> >>>>but now it is almost close enough to make my character
>>>> sweaty. I
>>>> >>>>also scaled down my ground plane a tad.
>>>> >>>>
>>>> >>>>Just using 1024 res and sample 20. And bog standard
>>>> antialiasing.
>>>> >>>>
>>>> >>>>So very BIG THANKS to all who replied!
>>>> >>>>
>>>> >>>>Joe Laffey wrote:
>>>> >>>>
>>>> >>>>
>>>> >>>>
>>>> >>>>>On Wed, 31 May 2006, Helen Bucknall wrote:
>>>> >>>>>
>>>> >>>>>
>>>> >>>>>
>>>> >>>>>>Is there a way to get shadow map shadows to stop
>>>> flickering even
>>>> >>>>>>when nothing is moving?
>>>> >>>>>>
>>>> >>>>>>This is what I have tried to no avail.
>>>> >>>>>>
>>>> >>>>>>On the spot light (cone angle less than 90):
>>>> >>>>>>Resolution up ( and down).
>>>> >>>>>>Softness up and down.
>>>> >>>>>>Samples up.
>>>> >>>>>>
>>>> >>>>>>None of these make any diference to the flickering.
>>>> >>>>>>
>>>> >>>>>>On the render panel:
>>>> >>>>>>I've played around with the antialiasing and jitter.
>>>> >>>>>>On the shadows page I've clicked off rebuild.
>>>> >>>>>>
>>>> >>>>>>
>>>> >>>>>
>>>> >>>>>If you view your scene from the light is there an
>>>> extremely large
>>>> >>>>>depth to the objects? In other words, are the closest
>>>> object to
>>>> >>>>>the light and the farthest object from the light
extremely
>>>> far
>>>> >>>>>apart? This can lead to ZDepth (used for shadowmaps)
>>>> presision
>>>> >>>>>issues in some renderers.
>>>> >>>>>
>>>> >>>>>This is often the case if you have a huge ground plane.
>>>> >>>>>
>>>> >>>>>You may be able to exclude some objects, to help, or
make
>>>> smaller
>>>> >>>>>versions that catch shadows.
>>>> >>>>>
>>>> >>>>>--
>>>> >>>>>Joe Laffey | Visual Effects for
Film and
>>>> Video
>>>> >>>>>LAFFEY Computer Imaging |
>>>> -------------------------------------
>>>> >>>>>St. Louis, MO | Show Reel
>>>> http://LAFFEY.tv/?e01274
>>>> >>>>>USA
>>>> >>>>>
>>>
---
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