photogrammetry

On-set tips: Creating high frequency detail by Xuan Prada

In a previous post I mentioned the importance of having high frequency details whilst scanning assets on-set. Sometimes if we don't have that detail we can just create it. Actually sometimes this is the only way to capture volumes and surfaces efficiently, specially if the asset doesn't have any surface detail, like white objects for example.

If we are dealing with assets that are being used on set but won't appear in the final edit, it is probably that those assets are not painted at all. There is no need to spend resources on it, right? But we might need to scan those assets to create a virtual asset that will be ultimately used on screen.

As mentioned before, if we don't have enough surface detail it will be so difficult to scan assets using photogrammetry so, we need to create high frequency detail on our own way.

Let's say we need to create a virtual assets of this physical mask. It is completely plain, white, we don't see much detail on its surface. We can create high frequency detail just painting some dots, or placing small stickers across the surface.

In this particular case I'm using a regular DSLR + multi zoom lens. A tripod, a support for the mask and some washable paint. I prefer to use small round stickers because they create less artifacts in the scan, but I run out of them.

I created this support while ago to scan fruits and other organic assets.

The first thing I usually do (if the object is white) is covering the whole object with neutral gray paint. It is way more easy to balance the exposure photographing again gray than white.

Once the gray paint is dry I just paint small dots or place the round stickers to create high frequency detail. The smallest the better.

Once the material has been processed you should get a pretty decent scan. Probably an impossible task without creating all the high frequency detail first.

On-set tips: The importance of high frequency detail by Xuan Prada

Quick tip here. Whenever possible use some kind of high frequency detail to capture references for your assets. In this scenario I'm scanning with photos this huge rock, with only 50 images and very bad conditions. Low lighting situation, shot hand-held, no tripod at all, very windy and raining.
Thanks to all the great high frequency detail on the surface of this rock the output is quite good to use as modeling reference, even to extract highly detailed displacement maps.

Notice in the image below that I'm using only 50 pictures. Not much you might say. But thanks to all the tiny detail the photogrammetry software does very well reconstructing the point cloud to generate the 3D model. There is a lot of information to find common points between photos.

The shooting pattern couldn't be more simple. Just one eight all around the subject. The alignment was completely successfully in Photoscan.

As you can see here, even with a small number of photos and not the best lighting conditions, the output is quite good.

I did an automatic retopology in Zbrush. I don't care much about the topology, this asset is not going to be animated at all. I just need a manageable topology to create a nice uv mapping and reproject all the fine detail in Zbrush and use it later as displacement map.

A few render tests.

Meshlab align to ground by Xuan Prada

If you deal a lot with 3D scans, Lidars, photogrammetry and other heavy models, you probably use Meshlab. This "little" software is great managing 75 million polygon Lidars and other complex meshes. Photoscan experienced users usually play with the align to ground tool to establish the correct axis for their resulting meshes.

If you look for this option in Meshlab you wouldn't find it, at least I didn't. Please let me know if you know how to do this.
What I found is a clever workaround to do the same same thing with a couple of clicks.

  • Import your Lidar or photogrammetry, and also import a ground plane exported from Maya. This is going to be your floor, ground or base axis.
  • This is a very simple example. The goal is to align the sneaker to the ground. I would like to deal with such a simple lidars at work :)
  • Click on the align icon.
  • In the align tool window, select the ground object and click on glue here mesh.
  • Notice the star that appears before the name of the object indicating that the mesh has been selected as base.
  • Select the lidar, photogrammetry or whatever geometry that need to be aligned and click on point based glueing.
  • In this little windows you can see both objects. Feel free to navigate around it behaves like a normal viewport.
  • Select one point at the base of the lidar by double clicking on top of it. Then do the same in one point of the base geo.
  • Repeat the same process. You'll need at least 4 points.
  • Done :)