A SELF-PORTRAIT OF YOUNG LEONARDO

THE DIGITAL RESTORATION OF A LEONARDO PORTRAIT

The digital restoration of a sketch in one of Leonardo da Vinci's notebooks reveals a possible self-portrait of the artist when he was young.

By Amelia Carolina Sparavigna, Dipartimento di Fisica, Politecnico di Torino

A sketch found in one of Leonardo da Vinci's notebooks could be a self-portrait. The drawing had been partially hidden by handwriting over it, and it remains unappreciated for 500 years before being noted by Piero Angela, the most famous Italian scientific journalist. After months of restoration work, an image was obtained showing the face of a young man. The restoration was performed on a digital image of the document, not on the document itself. From the image, the written notes have been removed, and the image was completed by a slight reconstruction of image edges. The portrait obtained after this procedure was aged using criminal investigation techniques and compared with the self-portrait of old Leonardo. After consultations with facial surgeons and police forensic experts, a general agreement arose on a strong similarity between the images.

The discovery

On Saturday February 27, 2009, during a prime-time entertainment show of the RAI broadcaster on history and science presented by his son Alberto, Piero Angela showed how he discovered the self-portrait of Leonardo Da Vinci. This self-portrait is hidden in a page of the Da Vinci's Codex on the Flight of Birds. Now held at the Biblioteca Reale of Turin, the Codex on the Flight of Birds is a relatively small codex by Leonardo, dated approximately 1505.

Angela said that when he was observing a copy of the manuscript written by Leonardo, he noticed that there was a drawing hidden between the words on the tenth page of the codex. First of all, the journalist noticed what looked like a nose underneath writing (see Fig.1). The fact that the drawing was made by a left-hand artist, as the directions of the sketching lines are showing, reinforced the necessity of further investigations. Enhancing the red-chalk sketch with the help a graphic artist, a portrait of a Renaissance man emerged. After months of micro-pixel work, the graphic designers gradually cancelled the text by making it white instead of black, revealing the drawing beneath. Angela realised that this could be a self-portrait of the young artist, and in fact, comparing the drawing with the Leonardo self portrait of c. 1512-15, the result is that the two men look like brothers.

Fig.1 Piero Angela initially discovered what looked like a nose in a page of the Codex on the Flight of Birds. If we remove the writing, the portrait appears.

The well-known researcher on Leonardo studies, Carlo Pedretti, agrees in considering the image as a self-portrait. Piero Angela explained the possible evolution of the artist's notebook as follows. Leonardo drew on the leaves, which constitute the eight central pages of the codex, between 1482 and 1489, when he was living at the court of Ludovico Sforza in Milan. Then these pages were 'recycled' by the artist to write his notes on the flight.

Work on pixels

Let us repeat the digital restoration, to understand what happened during the manipulation of pixels. Each pixel can have red, green and blue tones ranging from 0 to 255. Because the portrait is in red-chalk and the writing almost black, let us choose a threshold value for the red tone and set it to a certain value (for instance, 180). If the red tone has a value which is below the threshold value, we replace the pixel with a white pixel. The new image on which we can work further is shown in Fig.1 on the right: the hand-written text in now white.

After removing the written letters, we can work on the white pixels. A possible approach is the following. Let us consider a white pixel: we replace it if three pixels in its nearest neighbour are not white. The new pixel has the colour tones given by the averaged values of these three pixels. This reconstruction procedure is iterated until almost all the white pixels had been removed and we have the portrait as in Fig.2.

Fig.2 The result obtained after iterating the interpolation with nearest-neighbouring pixels (up). And after an enhancement using Iris (down).

The graphic artists engaged by Piero Angela obtained what we can consider a perfect result, after a great expenditure of micro-pixel work for several months. Here, we have proposed a simple approach based on interpolation with nearest neighbouring pixels, for the pleasure to repeat the discovery of Leonardo self-portrait.

The recent discovery of a Leonardo self-portrait is of course very important by itself. Being obtained by means of an image processing, it has another relevant value. It is showing the importance of digital restoration of old documents. This kind of restoration, which is not made on the document itself but on its digital image, can give excellent results, important for studies of art and palaeography.

More details at http://arxiv.org/abs/0903.1448

and also http://arxiv.org/abs/1111.4654

Superposition of the new self-potrait on the well-known self-portrait in red chalk.