7.4.5 Focal blur hexgrid constants
Hex_Blur1 = 7
Hex_Blur2 = 19
Hex_Blur3 = 37

I have two questions about this:
1. What are they used for?
2. I'd like to know how I might calculate Hex_blur4, Hex_blur5 etc etc
3. When using focal blur, does blur_samples 8 look worse blur_samples 7?

Regards,
Apache

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Apache wrote:
> 7.4.5 Focal blur hexgrid constants
> Hex_Blur1 = 7
> Hex_Blur2 = 19
> Hex_Blur3 = 37
> 
> I have two questions about this:
> 1. What are they used for?
> 2. I'd like to know how I might calculate Hex_blur4, Hex_blur5 etc etc
> 3. When using focal blur, does blur_samples 8 look worse blur_samples 7?
> 

I don't know what they are, but I used my TI-86 to find that the points 
(1,7), (2,19) and (3,37) fit on the curve y = 3x^2 + 3x + 1 where x 
would be the x in Hex_Blurx and y would be the constants.
According to the above equation, Hex_Blur4 would be 61, Hex_Blur5 would 
be 91 and Hex_Blur6 would be 127.
I used the quadratic fit because it gave 7, 19 and 37 extactly.  The 
other fits like linear and logrithimic gave correlations of .99 or .97.

Brendan

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Brendan Ryan wrote:
>Apache wrote:
>> 7.4.5 Focal blur hexgrid constants
>> Hex_Blur1 = 7
>> Hex_Blur2 = 19
>> Hex_Blur3 = 37
>>
>> I have two questions about this:
>> 1. What are they used for?
>> 2. I'd like to know how I might calculate Hex_blur4, Hex_blur5 etc etc
>> 3. When using focal blur, does blur_samples 8 look worse blur_samples 7?
>>
>
>I don't know what they are, but I used my TI-86 to find that the points
>(1,7), (2,19) and (3,37) fit on the curve y = 3x^2 + 3x + 1 where x
>would be the x in Hex_Blurx and y would be the constants.
>According to the above equation, Hex_Blur4 would be 61, Hex_Blur5 would
>be 91 and Hex_Blur6 would be 127.
>I used the quadratic fit because it gave 7, 19 and 37 extactly.  The
>other fits like linear and logrithimic gave correlations of .99 or .97.
>
>Brendan
>
Um, a quadratic fit with only three points will ALWAYS fit those three
points exactly.  When your fit model has the same number of points as your
data set, the model will always fit exactly and yet will be basically
meaningless.  Or to be more blunt, the parabola found here is no more
meaningful than the line you'd get from fitting a set of two points.  It
might be the best you can do, given the limited data set, but there's no
reason to believe it reflects the underlying structure.

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I was about to say that. I think I'll figure it out myself. I'll let you
guys know when I'm done.

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>>
> 
> Um, a quadratic fit with only three points will ALWAYS fit those three
> points exactly.  When your fit model has the same number of points as your
> data set, the model will always fit exactly and yet will be basically
> meaningless.  Or to be more blunt, the parabola found here is no more
> meaningful than the line you'd get from fitting a set of two points.  It
> might be the best you can do, given the limited data set, but there's no
> reason to believe it reflects the underlying structure.
> 

Oh sorry about that, I wasn't thinking. :(  It takes 2 points to define 
a line and 3 for a parabola, how could I have forgetten. :(

Brendan

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Brendan Ryan wrote:
> Apache wrote:
>> 7.4.5 Focal blur hexgrid constants
>> Hex_Blur1 = 7
>> Hex_Blur2 = 19
>> Hex_Blur3 = 37
>>
>> I have two questions about this:
>> 1. What are they used for?
>> 2. I'd like to know how I might calculate Hex_blur4, Hex_blur5 etc
>> etc 3. When using focal blur, does blur_samples 8 look worse
>> blur_samples 7?
>>
>
> I don't know what they are, but I used my TI-86 to find that the
> points (1,7), (2,19) and (3,37) fit on the curve y = 3x^2 + 3x + 1
> where x would be the x in Hex_Blurx and y would be the constants.
> According to the above equation, Hex_Blur4 would be 61, Hex_Blur5
> would be 91 and Hex_Blur6 would be 127.

Thinking about what hexgrid might mean points in the direction that this
equation is correct. (Monospace font needed to correctly view the ASCII
art below.)

 * *
* * *  X=1, Y=7
 * *

  * * *
 * * * *
* * * * *  X=2, Y=19
 * * * *
  * * *

   * * * *
  * * * * *
 * * * * * *
* * * * * * *  X=3, Y=37
 * * * * * *
  * * * * *
   * * * *

Try making bigger ones, and you'll see that they fit the equation
perfectly...

Rune
--
3D images and anims, include files, tutorials and more:
rune|vision:  http://runevision.com **updated Jul 25**
POV-Ray Ring: http://webring.povray.co.uk

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And now for the usage of those values..... what's the use of those values?

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On Sun, 24 Aug 2003 17:00:39 +0200, "Apache"
<apa### [at] yahoocom> wrote:

>And now for the usage of those values..... what's the use of those values?

I think there is a special provision in the source code for these
numbers, meaning that if you use a hexagonal number of blur_samples,
they will not be distributed randomly but rather in a regular
hexagonal pattern.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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