Wagon Plates – Step 2

Hi again,

Today I show you the second step of the restoration of our Etruscan plates.

Once understood the technology behind their realization, I had to create a digital copy of each plate. The easiest way to create a 3D model totally identical to a real object is not to create a 3D model! This pun describes quite well what I did. As a matter of fact I created a depth map.

The depth map of an object is a black and white image that contains information relating to the distance of its surfaces from a viewpoint. The depth map shows luminance in proportion to the distance of each point of the object from the camera: nearer surfaces are lighter while further surfaces are darker. The depth map of a surface contains all the information needed to create related applications, such as normal maps or displacement maps.

Depth map.
In black are the further surfaces while the nearer are lighter.

The normal map is an RGB image that intends to create the illusion of 3D viewing. It contains, for each pixel, information on the direction of its normal. By reading the percentage of each colour in the pixel, the software knows its exact position in the space and is able to simulate a three dimensional image. The use of normal maps is extremely helpful in very complex scenes, especially when they have to be explored with real-time applications, since they allows a highly detailed result using a small number of polygons.

Normal map.
The colour of each point gives information about the position of its normal.

Simulation of 3D.
This brickwall is actually a flat surface generated by the normal map.

Depth maps can also be used as Displacement maps to create a 3D objects. In this process each point over the surface is displaced in its actual geometric position according to its value of black and white. Displacement maps are less used than normal maps in real-time application, as they required a high number of micro-polygons on the surface to match the size of the pixel on the screen.

3D object from a depth map.

To create the depth map of the plates I used Photoshop. I opened the picture of a lamina and created on it a layer of grey, which is an intermediate tone that allows the addition of both lighter and darker colours on it.

The path is drawn on the picture in order to obtain a result as closer as possible to the real object.

Drawing of the guilloches path with the Pen tool in Photoshop

Firstly I focused on the creation of the external guilloches. I drew each of them using the pen tool on a path layer and then I use the option Stroke Path that allowed me to obtain a new layer with the lines in the desired colour and thickness.

Stroked Path

Then I focused on the rosettes. I tried and tried again to obtain a good depth map of them by drowning them with Photoshop, but unfortunately the results I got were always unsatisfactory in a 3D model: they were always too far away from the real object.

Then I had to invent something different. I will show you what I did in the next post!

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