Inconsistent FOV (perspective) between ZBrush and Maya

wren945

I'm designing my character for a game for Unreal Engine. Games usually have a big FOV (angle of view), such as 90 degrees typically. I set FOV to 90 in UE, Maya. and ZBrush. The perspective in Unreal Engine and Maya is about the same. But much different in ZBrush - it has much less "fish eye" effect.

To demonstrate this, I set the FOV to a crazy high value of 150 degrees and took these pictures. You can see the difference.


I'd say, of the two, ZBrush is wrong, because with such a value, you are expected to see some distortion. Actually, when you change FOV from 1 to 179 (min and max allowed), you see very little perspective change in ZBrush, which is not the case even in real-life cameras.

The inconsistency makes it hard to design a character's face. How do you deal with this problem? I think many people working on ZBrush work for games.

Axi5

Maxon's documentation seems to be vague and I'd argue wrong about focal length

Angle of View
Angle Of View controls the strength of the perspective effect. As with camera lenses, a short focal length gives the strongest perspective, and a long focal length the least.

From: Draw

Here's a good image showing the relationship:

Here's an old article exploring the same thing as you:

Sort a Done. Its almost there... I swear...: ZBrush Focal Angle

Fov can also be horizontal or vertical, and I haven't used Maya in a while so I can't remember which of these it is

wren945

Axi5 said:

Maxon's documentation seems to be vague and I'd argue wrong about focal length

Angle of View
Angle Of View controls the strength of the perspective effect. As with camera lenses, a short focal length gives the strongest perspective, and a long focal length the least.

From: Draw

Here's a good image showing the relationship:

Here's an old article exploring the same thing as you:

Sort a Done. Its almost there... I swear...: ZBrush Focal Angle

Fov can also be horizontal or vertical, and I haven't used Maya in a while so I can't remember which of these it is

Thanks for the information and the blog link. In the later version of ZBrush, I can change either focal length or FOV, and the other one will be updated accordingly automatically; I don't have to look up or calculate. My problem is that, given any FOV or its derived focal length, the perspective distortion effect is far less than in other applications like Maya or Unreal Engine, even if I force an extreme value.

Axi5

I need to check that out, I've only just got back into 3D and picked up Zbrush for Ipad...

Anyway just to rule it out you haven't disabled perspective have you?

Also if it is infact Focal Length you're adjusting in Zbrush rather than angle, then I'd expect higher values to have less distortion (as in that image above), so double check your Maya settings.

wren945

Axi5 said:

I need to check that out, I've only just got back into 3D and picked up Zbrush for Ipad...

Anyway just to rule it out you haven't disabled perspective have you?

Also if it is infact Focal Length you're adjusting in Zbrush rather than angle, then I'd expect higher values to have less distortion (as in that image above), so double check your Maya settings.

I'm sure perspective is turned on, because I DO see perspective change when tweaking it, just not as strong as Maya.
Yes, smaller focal length = bigger fov = stronger distortion.

pior

This is an issue as old as time (or rather, as old as Zbrush) and AFAIK there is no fix for it, as the Zbrush FOV values do not really represent anything and you won't be able to get a real analog to a 3d viewport since their projection/rendering isn't really 3D. I've seen it negatively affect the work of extremely skilled artists, as in seen it with my own eyes at the office when looking at their work, including the surprise when loading up the model in Maya. You'll find mention of this online a plenty, dating all the way back to early Zbrush 3/4 releases.

This was actually one of the main reasons that personally made me drop Zbrush in favor on Mudbox (and now Blender), as I find that working this way is borderline absurd.

I suppose it would affect figurine sculptors less, since their work is ultimately shown very small IRL hence seen similarly to through a telephoto lens (therefore similar to ortho). And indeed, many people using Zbrush for CG do manage to live with the issue, but it does involve doing frequent exports to a regular 3d software, at least for heads.

All that said, good luck ! You'll find your own workaround.

Eric Chadwick

If I recall correctly, ZBrush started out as purely 2.5D with the whole "pixols" tech which was basically color plus some height data.

They added 3d meshes that you could stamp down into pixols on the canvas. But it was still an orthographic view mode. Then people were manipulating 3d models more, and not stamping them down into the canvas, and asking for perspective view.

So they kind of hacked it into the existing display system. Which had always been super powerful at displaying millions of polygons, so why ditch that? Anyhow that's my understanding for why their perspective view doesn't work quite as expected.

Neox

Zbrush just simply has no camera. The FOV is a perspective skew in a orthographic projection. You can see this happening when you reimport the same mesh but with a lot bigger bounds. Like adding a cube 10 meters away from your character (or whatever)
Another way of showing that it isnt a camera is, that its impossible to move the camera between 2 meshes or 2 parts of a mesh, say in a horse the camera can not be between the front and the hind leg. One will always overlap the other.

The best you can do is regularly checking your work with a "real" camera and distortion 

wren945

Neox said:

Zbrush just simply has no camera. The FOV is a perspective skew in a orthographic projection. You can see this happening when you reimport the same mesh but with a lot bigger bounds. Like adding a cube 10 meters away from your character (or whatever)
Another way of showing that it isnt a camera is, that its impossible to move the camera between 2 meshes or 2 parts of a mesh, say in a horse the camera can not be between the front and the hind leg. One will always overlap the other.

The best you can do is regularly checking your work with a "real" camera and distortion 

Thanks for the explanation. Good to know. I'm surprised at how this is the case when ZBrush is number one digital sculpting application.

Neox

It is a 2.5d illustration tool that offered the ability to tweak the tools you can use in your illustrations and eventually grew from there