SuperSonic

[hapf]

Locations like these are tough because they need so many secondary references. Embedded Julia sets within embedded Julia sets.
http://www.fractalforums.com/index.php?action=gallery;sa=view;id=18899

[Dinkydau]

Nice. Black and white really suits it

[hapf]

It does. But it also allows to quickly have a decent picture while multi colour often needs a lot of tweaking to look
satisfactory.  Good anti aliasing gives such locations an almost surreal touch. Without it looks very rough.

[quaz0r]

for these do you supersample any or just use a sobel filter?  i remember claude said he enjoys not doing any supersampling.  i found the sobel filters in the image lib im using but i havent played around with it yet to figure out what parameters to pass it.

[claude]

I've come round to the need for supersampling in dense locations to reduce Moiré artifacts...

[hapf]

for these do you supersample any or just use a sobel filter?  i remember claude said he enjoys not doing any supersampling.  i found the sobel filters in the image lib im using but i havent played around with it yet to figure out what parameters to pass it.

I don't think that any (linear) filters can replace supersampling for fractals. Too much loss of fine detail if you want to get rid of the aliasing this way. I do 32K versions for massive oversampling for 4K and 8K. But even that is not enough for some locations that are too dense with structure. Here only colouring that tones down aliasing helps.
Concerning leaving the aliasing in it is an option with some locations and colouring choices that might look "better" that way than with anti aliasing. A subjective esthetic choice.

[quaz0r]

hear hear    i like to go overboard just to make sure its as good as it can be.  i used to use 16x supersampling even on 4k images but then i decided 12x or sometimes even 8x is sufficient     using that much helps the most when you use the escape time to pick colors or such.

[Dinkydau]

The amount of supersample is very limited by the software, usually.

[quaz0r]

bummer.   

[hapf]

hear hear    i like to go overboard just to make sure its as good as it can be.  i used to use 16x supersampling even on 4k images but then i decided 12x or sometimes even 8x is sufficient    using that much helps the most when you use the escape time to pick colors or such.

32K is not necessarily overkill. For the following location it's about enough for 2K but not enough for 4K! That would apparently need 64K, and 8K 128K.  

http://www.fractalforums.com/index.php?action=gallery;sa=view;id=18961

[quaz0r]

yeah, so 16x.  i definitely approve   

[billtavis]

just wanted to throw in my two cents that adding a slight Gaussian blur prior to downsizing helps a lot. A small radius blur at 4x bigger is going to be much faster to render than no blur at 8x bigger. It would be worth doing some side-by-side tests to see if there is a visual difference. I'm not sure exactly how to find the optimal blur radius other than trial and error — if it is too large the resulting image will be too soft, obviously.

By combining a small Gaussian blur with a better resizing filter, like Lanczos, I've never had a need to go above 6x supersampling, and often 4x is plenty good.

[quaz0r]

indeed, proper downsampling involves a blur operation first.  i use a gaussian blur prior to downsampling also.  and yeah, ive not been sure either what the exact blur settings should be.  ive been meaning to ask around if anyone has any thoughts on that.  what ive been doing is to set the blur equal to half the supersampling amount.  it seems to turn out to my taste anyway.  and yeah, a good sampling filter is also a must.  ive taken a liking to and have been using Jinc.  i find the simpler and more common ones to give subpar results, especially when you are taking the loads of extra time it takes to render that extreme amount of supersampling.

as far as how much supersampling to use, well, people seem to have different tolerance thresholds for what they think is perfect or even good enough.  if you are rendering just based on DE, less supersampling is needed to get pretty good results.  if you are coloring based on escape time, well personally i find anything <= 8x subpar.  12x seems like it is probably always good enough, but i often do 16x ...well, just because i can.  

honestly, ive observed that a lot of people who are into rendering are resistant, certainly at first, to the notion of supersampling, especially the notion of doing it in large amounts, simply because if they were to accept it, it would mean A) that theyve basically been doing it wrong thus far,  and B) if they were to do it properly going forward, it is going to take a whole lot longer to accomplish less than they are used to.  

all the junk people post on deviantart for instance, they always add a note in the description instructing you to click on the image to view it full size so you can see all the details.  when i see the initial scaled down image i usually think, hey, that looks pretty good.  then when i click to view it at full res, my eyes spontaneously combust as my senses are overloaded with all that horrible awful aliasing and distinct LACK of detail.  as the blood pours from my eyes i quickly try to escape back to the scaled down image as fast as humanly possible..   

[hapf]

I have not used blur so far since blur reduces detail anywhere, needed or not. Blur could be helpful when applied only where there is so much detail that oversampling alone needs massive amounts. So the blur would have to be adaptive. And the colouring can promote or reduce aliasing as well. I don't see why escape time would be more critical than DE for aliasing, though. I use Catrom filter for downsampling and add a slight unsharp mask.

[quaz0r]

applying a lowpass filter prior to downsampling is sort of an axiom of image processing.

Gaussian blurring is commonly used when reducing the size of an image. When downsampling an image, it is common to apply a low-pass filter to the image prior to resampling. This is to ensure that spurious high-frequency information does not appear in the downsampled image (aliasing). Gaussian blurs have nice properties, such as having no sharp edges, and thus do not introduce ringing into the filtered image.

if you imagine something like 256 samples (16x supersampling) combining into one pixel in the final image, you definitely could think of it in terms of information loss.  this is simply the nature of the beast.  employing some pre-sampling filtering is about controlling how that information will combine to produce the end result.  thinking of it in terms of information loss is just not really the right way to think of it.

as far as escape time coloring, it simply requires a ton of sampling to get smooth consistent coloring free of spurious garbage, moreso than simple distance shading.  i suppose one could post some example comparison shots if they were so inclined.