Jagged edge on metal spec

[Rhys]

Any idea how to get rid of this jagged line, scene setup is hdri lit, reinhard .3 no clamp or sub pixel mapping on.



tried turning on sub pixel mapping on, the area isn't clamped as the pixel info is only at .6 float

Rendered with AA at 1-100 noise 0.003 area aa on. Its apparent on the spec pass

any ideas?

[joconnell]

So!

This is one of the many problems we get with images being made up from pixels. What you've got is a thin metal bar which is only about 2 or 3 pixels wide. You've got a bright, lit side and then a dark side too. Anti-aliasing is supposed to do some smoothing / blurring to try and make the transitions between areas of contrast a bit nicer so if you've got a bright value beside a dark value, anti-aliasing will try and make some mid values between the two to smooth things out. Here you've got a sharp strip of highlight and you just don't have enough pixels to fit any of those in the middle anti aliased values.

So what choices have you got? The anti aliaser is really doing it's job properly here, it's coming back with what the correct result is, it's just getting bit by not having a large enough surface area to gradually go from highlight to shadow. So you can either make the pipe / rod thicker so it's got more surface area for your highlight to fall off on, you can make the reflections of the pipe glossier so it blurs out more (mighty not have a huge effect), you can make the light source hitting it bigger so it wraps around a tiny bit more, you can use a softer anti aliaser like video or quadratic (that's a good point - are you using a sharp filter like mitchell that might be making the edge even harsher?) so there's less contrast on the edge, or finally you can use something like glare / glow in post or in the lens effects to soften / take the edge off this little specular hit.

[Art48]

To avoid that issue we started to clamp at 1.0 and use sub-pixel-mapping and max ray intensity at the default value.
We got rid of it at the cost of no floating point renders :-/

[Rhys]

Thanks will give the AA blur a try, what's annoying is that the highlight isn't super bright so adding any glow affects looks a little odd! It was rendered at 5k maybe 6k would give the AA more room to play with, will try a softer filter first. Dont really want to start clamping and turning sub pixel on!!

[joconnell]

Yeah I think it's kind of just a surface area / limited amount of pixel space to smooth things over. Slightly larger filter value on your AA or something blurrier should do it.

Another trick which works if you've got a blur you can drive using a matte is to run the image through an edge detect which will typically pick up any of the crisp edges, then you can use this as a matte to blur only those crisp edges.

[tricky]

You are also zoomed in at 200% in that image. Is it so noticeable at 100%?

[Deflaminis]

Excellent post Joconnel

[Joelaff]

I like the "Soften" (Gaussian) image filter for this (and almost every render). Set the radius to 3.5-4.5, where under 4.0 (e.g.3.98 ) is slightly faster. Makes everything look more photographic, as even the finest real world lenses simply are not that sharp.