I find I get better results by rendering at a massively larger scale 
(often as much as 8 or 16 times larger in each dimension), and then 
downsizing in the GIMP. Of course, I rarely use POV for anything that 
takes more than a few minutes these days...

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On occasion, I've done that as well-- downsizing large renders in Photoshop,
using bicubic interpolation there--with pretty good results (compared to using
POV-Ray's 'default' AA with its settings of type 1, threshold of 0.3, and
jittering on.) But I don't use AA's default settings, as they are somewhat
crude, visually speaking.

Your question prompted me to do some more research, mainly about Photoshop's
various methods of downsampling-- bicubic interpolation vs. bilinear vs.
"nearest neighbor."

I looked at 'bicubic interpolation' and 'image scaling' at Wikipedia; the latter
leads me to believe that bicubic and bilinear methods may apply a slight bit of
useful blurring before the downsizing-- or rather, some low-pass filtering, to
help minimize the 'high-frequency' sharp color/brightness transitions between
pixels. That sounds a bit like AA, although not quite the same thing.

I just did a test with POV-Ray's included 'biscuit' scene file-- first rendering
it at 3200 X 2400 pixels with no AA, then again at 800 X 600 *with* AA (using
the defaults.) I then downsized the larger image, first using bicubic
interpolation, then bilinear. Comparing the resulting images close-up in
Photoshop, I actually prefer the bilinear method of interpolation-- it seems to
'match' the look of the smaller AA image better, regarding fine details, which
are retained (more or less.) Bicubic looks a bit *too* smooth--an interesting
discovery.

BTW, something I read long ago (and my own intuition) tells me that, when
downsizing an image, it's best not to use a straight 4-to-1 reduction (as in my
example), or a likewise purely linear reduction. In other words, to choose
something different (odd?), like 7-to-1 or 3-to-1, etc. If I recall correctly,
the interpolation works better this way(?), visually.

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On 4/9/2017 1:58 PM, Kenneth wrote:
> On occasion, I've done that as well-- downsizing large renders in Photoshop,
> using bicubic interpolation there--with pretty good results (compared to using
> POV-Ray's 'default' AA with its settings of type 1, threshold of 0.3, and
> jittering on.) But I don't use AA's default settings, as they are somewhat
> crude, visually speaking.

Good point, I need to look at updating my INI files again. I keep 
getting back to the default install for one reason or another.

> BTW, something I read long ago (and my own intuition) tells me that, when
> downsizing an image, it's best not to use a straight 4-to-1 reduction (as in my
> example), or a likewise purely linear reduction. In other words, to choose
> something different (odd?), like 7-to-1 or 3-to-1, etc. If I recall correctly,
> the interpolation works better this way(?), visually.

I suspect it has to do with locality, and that using a size which isn't 
a multiple of the smaller size would force pixels from a slightly larger 
area (including the border around the scaled pixel).

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Am 2017-04-09 11:48, also sprach Benjamin Chambers:
> I find I get better results by rendering at a massively larger scale
> (often as much as 8 or 16 times larger in each dimension), and then
> downsizing in the GIMP. Of course, I rarely use POV for anything that
> takes more than a few minutes these days...

I still use AA (no jitter).  Since I have about 28,000 frames to deal 
with, loading each into gimp would be a pita!  Maybe ImageMagick/netpbm 
would be an option for your me for your cool idea...

-- 
dik

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On 9-4-2017 17:48, Benjamin Chambers wrote:
> I find I get better results by rendering at a massively larger scale
> (often as much as 8 or 16 times larger in each dimension), and then
> downsizing in the GIMP. Of course, I rarely use POV for anything that
> takes more than a few minutes these days...

Always AA, even for testing :-)

Out of curiosity: what do you use "for anything that takes more than a 
few minutes these days..."?

-- 
Thomas

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> I find I get better results by rendering at a massively larger scale
> (often as much as 8 or 16 times larger in each dimension), and then
> downsizing in the GIMP. Of course, I rarely use POV for anything that
> takes more than a few minutes these days...

Have you tried out all the AA settings?

eg something like "+a0.0 +am2 +r4" should give comparable results to 
rendering 16x larger in each direction with no AA and then resizing.

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On 4/13/2017 12:44 AM, Thomas de Groot wrote:
> Out of curiosity: what do you use "for anything that takes more than a
> few minutes these days..."?

Sadly, I just don't.

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dick balaska <dic### [at] buckosoftcom> wrote:
> Since I have about 28,000 frames to deal
> with, loading each into gimp would be a pita!  Maybe ImageMagick/netpbm
> would be an option for your me for your cool idea...
>

I have GIMP as well, but I'm *much* more familiar with Photoshop; it seems more
intuitive to me.

In PS, there is an 'Actions' feature that I use a lot-- for setting up a series
of operations on an image (like downsizing, for example) which can then
automatically carry out those steps very fast, on thousands of images. I haven't
gotten deeply enough into GIMP to know if it can do that, although I suspect it
can.

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On 4/12/2017 9:55 PM, dick balaska wrote:
> Am 2017-04-09 11:48, also sprach Benjamin Chambers:
>> I find I get better results by rendering at a massively larger scale
>> (often as much as 8 or 16 times larger in each dimension), and then
>> downsizing in the GIMP. Of course, I rarely use POV for anything that
>> takes more than a few minutes these days...
>
> I still use AA (no jitter).  Since I have about 28,000 frames to deal
> with, loading each into gimp would be a pita!  Maybe ImageMagick/netpbm
> would be an option for your me for your cool idea...
>

XnView or IrfanView can rescale a whole directory full of images.


Mike

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On 4/9/2017 11:48 AM, Benjamin Chambers wrote:
> I find I get better results by rendering at a massively larger scale
> (often as much as 8 or 16 times larger in each dimension), and then
> downsizing in the GIMP. Of course, I rarely use POV for anything that
> takes more than a few minutes these days...

I use default AA settings because I'm lazy.


Mike

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