ZBrushCentral

About the Nature of Pixols

ZBrush Usage Questions
#1

Some people have seemed a bit confused about how pixols and 3D objects work in ZBrush, not to mention what happens with cast shadows, so I thought I’d draw some diagrams and discuss it here. If any of my assumptions are incorrect, please do correct me.

About the Nature of Pixols

When you edit a 3D object it is fully rotateable. If you were able to view the canvas “from the side”, editing a 3D sphere in front of the canvas would look like this:

[img]http://www2.zbrushcentral.com/uploaded_from_zbc/200311/user_image-1068205211qnk.gif[/img]

But what happens when you Snapshot a 3D object into the canvas? It gets converted into Pixols very much the same way a vector shape becomes Rasterized in Photoshop, with one exception: The depth information is still there. However, pixol depth information is “one-sided”, there is no “back side”. What it means in practice is this:

[img]http://www2.zbrushcentral.com/uploaded_from_zbc/200311/user_image-1068205259iqw.gif[/img]

Think of the canvas as a computer generated landscape. Pixol information has no back side. There can be only one depth value per pixol, so within one layer, one pixol cannot be behind another - that requires a separate layer. Thus, once you’ve snapshotted a sphere into the canvas, it becomes a hemispherical dome shape embedded into the pixol canvas. On other words, it becomes a part of the canvas.

This also explains why the cast shadows look the way they do in ZBrush:

[img]http://www2.zbrushcentral.com/uploaded_from_zbc/200311/user_image-1068205352oua.gif[/img]

Due to the way they are calculated, shadows cannot be cast from one layer to another. Therefore the layers must be Flattened for rendering if shadows need to be present. And since Flattening combines all the layers into one, one pixol cannot be behind another, thus cast shadows and transparency are not possible within one scene.

If you want the objects to really look separate from the rest of the work shadow-wise, the ZMode can help you work your way around this. ZMode works by assuming that all “vertical surfaces” (ie pixols that are completely perpendicular) do not exist and are left out of the shadow calculation:

[img]http://www2.zbrushcentral.com/uploaded_from_zbc/200311/user_image-1068205407njb.gif[/img]

But since the pixol information has no backside, the ZMode shadows end up looking thinner than the visible top side would suggest.

When you 3D Skin an object, a similar procedure is made, but with one exception: The pixol data is mirrored, resulting a symmetrical 3D object:

[img]http://www2.zbrushcentral.com/uploaded_from_zbc/200311/user_image-1068205439oqd.gif[/img]

I stand to be corrected. :slight_smile:

#2

Seems Pixo “logic” :smiley:
Pilou

#3

thanx skaven, this really help me to understand whats going on while I´m rendering my pictures. I think, I understood whole thing except one. What exactly is ZMode? How to activate it? I didn´t get this point…

I wasn´t able to understand, why shadows are placed that way as they are. For example, if I planted trees on a terrain, their shadows was very large. How to avoid this? Is the ZMode answer?

thanx
vox

#4

Vox, ZMode is in the Lights:Shadow palette.

Here is a tutorial:

Light (shadow) Tutorial

#5

This is an excellent explanation with very illuminating illustrations. :slight_smile: Thank you for taking the time to put this together.

#6

So my assumptions about the way pixols work are correct? Glad to hear that, and also glad that this has turned out helpful for some people.

#7

Very nice illustration of the workings of Pixols. I mentioned this in another thread, but I’ve always thought of them in terms of those little toys where you have a grid of metal pins, and when you press your hand on the back of them it pushes the pins up in the shape of your hand. That’s Pixols in regular mode; in Zmode you lose the pins, and just have the pin heads floating in space. Your explanation is quite a bit clearer, though. Aurick and Pixolator–maybe you could include that in the next version of the manual. :slight_smile:

#8

My thoughts exactly! :+1: I have a toy like that in my room as well.

#9

Interesting thread. Good info to posess.

G

#10

that def helped me out man, thanks!

#11

I know its an old post, but very helpful, much appreciated explanation.

Andy.