Tag Archives: displacement maps

The holmos and lebes digitally restored

28 Nov

The bronze holmos of the Regolini-Galassi tomb is a very elaborated and beautiful object that has suffered significant damage and corrosion.

bronze holmos

Bronze holmos from the Regolini-Galassi tomb (photo: Vatican Museums)

To reveal the beauty of this object, we have unwrapped its decoration and used this image to create the line drawing of the engraved decoration.  Based upon this engraving and upon detailed study of the applied embossing, we have created a displacement map of the decoration of each of the parts of the holmos.

holmos unwrapped texture

Unwrapped decoration of the holmos cone (image: Visual Dimension bvba)

The displacement map is created in the same way as for the other objects: we simulate the engraving and embossing process in different layers of a Photoshop image, that is overlaid on the unwrapped texture.

Depth map holmos cone

Displacement map of the holmos cone (image: Visual Dimension bvba)

The displacement map is transformed into a normal map in Unity3D, giving a very nice real time rendering of the bronze object.

DROMOS8_new

Digitally restored holmos, placed in the Regolini-Galassi tomb (image: CNR-ITABC)

Digitally restored holmos, placed in the Regolini-Galassi tomb (image: CNR-ITABC)

DROMOS10_new

Digitally restored holmos, placed in the Regolini-Galassi tomb (image: CNR-ITABC)

The 6-headed lebes also suffered deformation and damage, so we performed digital restoration on this object as well.

6-headed lebes

Bronze six-headed lebes from the Regolini-Galassi tomb (photo:Vatican Museums)

In this case, we derived the unwrapped texture from a 3D model that was made from dense stereo matching on a set of photographs taken with an object tent.

3D photography of the lebes

Photography of the lebes in an object tent for creating the 3D model (photo: Vatican Museums)

detail of lebes

Detail of the engraving of the lebes (photo: Vatican Museums)

We first identified the full engraving of the lebes on the unwrapped texture, completing the missing parts.  Then, we painted the embossed features in a similar way as the other objects, through observation of those features on the many photographs taken.

lebes_depth_map_comp

Displacement map superimposed upon the unwrapped texture of the lebes (image: Visual Dimension bvba)

The displacement map was imported in Unity3D and translated into a normal map for real time visualisation (see images below, compare with images above).  All digitally restored objects are integrated in the new version of the application.

digitally restored six-headed lebes

Digitally restored six-headed lebes (image:CNR-ITABC)

Digitally restored six-headed lebes

Digitally restored six-headed lebes (image:CNR-ITABC)

This blog is part of the Etruscanning 3D project, that is being partially funded with support from the European Commission. This blog reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

 

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The situla restored digitally

27 Nov

One of the outstanding silver objects from the Regolini-Galassi tomb  is a situla, a ritual bucket to contain holy water or milk.  The situla is only preserved partially and consisted of a wooden cilindrical bucket decorated with a silver cover showing three animals and palmettes, as the symbol of life.

Silver situla

Silver and wood situla of the Regolini-Galassi tomb (photo: Vatican Museums)

The silver decoration was found by the excavators in a fragmented state and recovered only partially.  Presumably, the situla was suspended in the triangular window opening (see image below) and when the situla fell down, it broke and many fragments that fell on the ground were destroyed by corrosion.

situla suspended in triangular window

Situla suspended in the triangular window of the tomb (image: CNR-ITABC)

We digitised the situla by turntable photography (so that the cylinder could be unwrapped as one image) and closeup photography, so that the hinge and the chain could be modelled in 3D by hand.  The main goal of unwrapping the cylindrical silver sheet was to digitally restore it.  The physical restoration has not been documented and dates back probably to the 19th century.

photographing the situla

Photographing the situla on a turntable at the Museo Etrusco Gregoriano (photo: CNR-ITABC)

The resulting photographs were assembled into one image, depicting the cylindrical surface of the situla.  As can be seen from the images below, the silver sheet has also been embossed and engraved.  The digital restoration focused on understanding the production process and improving the physical restoration, based upon that knowledge, as the parts that have been added do no contain any engraving or embossing.  It appeared also that a  few small parts of the original silver are missing (see for example the wing of the griffin below).

unwrapped decoration of situla

Unwrapped decoration of the situla (image: Visual Dimension bvba)

detail of situla decoration

Detail of the restored situla decoration, showing a griffin (image: Visual Dimension bvba)

The digital restoration was implemented through the creation of a displacement map, which is the most efficient technique to deal with embossed and engraved objects (see also our blog post on the digital restoration of a patera).  In Photoshop, we created extra layers on top of the unwrapped situla decoration image, one layer for the engraving, one layer for the embossing.  Additional layers have been introduced to simulate the deformation of the metal when engraving. We also created a transparency map to indicate the form of the cutouts in the silver sheet.

restored depth map

Digitally restored displacement map of the situla (by Visual Dimension bvba)

Study of the unwrapped image showed that the palmettes were made by hammering the shape with a tool in the form of the palmette.  This production process was simulated in Photoshop.  The resulting transparency and displacement maps are used in the interactive real time visualisation system that has been implemented by CNR-ITABC (see image below).

digitally restored situla

The digitally restored situla in the Regolini-Galassi tomb (image: CNR-ITABC)

This blog is part of the Etruscanning 3D project, that is being partially funded with support from the European Commission. This blog reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

 

Digital restoration of a fragmented patera

23 Nov

The Regolini-Galassi tomb contained several outstanding silver and gold objects, now preserved in the Museo Gregoriano Etrusco in the Vatican.  One of the most interesting objects is a patera, in silver and plated gold, that was nailed to the wall of the tomb (see image below, showing its restored state, inv. nr. 20364) and that was uses for libation offers in religious rituals.  This patera most probably broke in pieces when being hit by stones from the collapsing roof in the cella of the tomb.

silver patera

Restored silver and gold patera from the Regolini-Galassi tomb (photo:Daniel Pletinckx)

silver patera - detail

Detail of this silver patera showing the nail hole and the deformation of the pieces (photograph: Daniel Pletinckx)

This patera is one of a set of silver objects from this tomb that are being produced in a Phoenician style with Egyptian decorations.  A very similar patera is preserved in the National Museum of Antiquities in Leiden, the Netherlands, and has been integrated in the exhibition “Etruscans: Emminent Women, Powerful Men” next to the Etruscanning VR installation that shows the virtual Regolini-Galassi tomb.  The provenance of this patera is unknown but scholars believe it originates from the Etruscan Barberini tomb, that has been excavated in 1855 and is dated around 630 BC.

Patera and lebes

Patera and lebes in the Leiden exhibition on the Etruscans (photo: Daniel Pletinckx)

patera RMO Leiden

Etruscan patera in Phoenician style in RMO Leiden (photo: Daniel Pletinckx)

As all objects in the 3D virtual reconstruction of the Regolini-Galassi tomb are visualised in their original state at the closing of the tomb, extensive digital restoration is needed for most objects.  As the 3D visualisation of the RG tomb happens in real time, and as we want the digitally restored objects to have very fine detail, we developed an innovative digital restoration technique that can be applied to most of the objects of the tomb.  This technique simulates the surface details of the objects (such as engraving, embossing, …) and turns them into a very efficient visualisation that can be used in real time systems.

So, let’s have a look at the digital restoration of the above mentioned patera.  We start with the drawings by Grifi in 1841 of the first restoration of the patera and an improved restoration by the restoration labs of the Vatican Museums in 1999.

drawing

Drawing of the first restoration of the patera by Luigi Grifi, 1841 (image: Vatican Museums)

patera restoration by Grifi - 1841

Drawing of the first restoration of the patera by Luigi Grifi, 1841 (image: Vatican Museums)

Improved restoration 1999

Improved restoration by the Vatican Museums, 1999, drawn by L. di Blasi (image: Vatican Museums)

When comparing both restorations, one can see that there are slight differences between these restorations but also that the 1841 drawings show more details than the 1999 restoration.  Possibly, some detail was lost in the first restoration or in undoing the first restoration.  When analysing the engravings, one can see that several motives are repeated one or more times, so that nearly always we can find information about missing parts by looking at other instances of the same drawing on another place of the engraving.  When doing so, very little uncertainty is left what to fill in, only a few details such as a bird or a tree have been filled in by analogy. We also compared closely with the similar patera from RMO, shown above, to come to the most probable digital restoration of the engraving (see drawing below).

Digital restoration

Digital restoration of the engraving of the patera (Visual Dimension)

In a second step, we simulated the production process of the patera by creating a displacement map from this engraving.  This displacement map shows as a black and with image the small height perturbations that are created by the engraving (and subsequent deformation of the metal around the engraved lines) on the front of the object and the embossing (created by hammering from the back of the object).  The embossing is created manually by simulating the impression of the blunt chisel, after studying carefully the high resolution images of the object (see image below).

Detail patera 20364

Detail of the patera with appropriate lighting to enhance engraving and embossing (photo: Vatican Museums)

All these different processes yield different displacement maps which are composed as layers in Photoshop.  The resulting displacement map is a  precise simulation of the relief of the complete, undamaged patera (see image below).

displacement map

Simulated displacement map of the whole patera (Visual Dimension)

The Etruscanning VR application uses Unity 3D as software to create and visualise the virtual tomb with its animated objects and narrated stories.  In Unity 3D, a displacement map can be transformed into a normal map, which allows to visualise very efficiently the relief of objects.  In this way, we visualise details of less than 1/10th of a milimeter on the surface of this object through a very lightweight 3D object (together with 80 other 3D objects) in a realtime system, running on a small, cheap computer (in our case a  Mac mini).  On the other hand, displacement maps are an optimal and easy approach for digital restoration.

reconstructed patera

3D visualisation test of the digitally restored patera (CNR-ITABC)

In the Leiden exhibition, the digitally restored patera can be confronted with the similar patera from the Barberini tomb, on display next to the VR installation, showing the added value of digital museum objects.

This blog is part of the Etruscanning project, that is been funded with support from the European Commission. This blog reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.