Image Processing

The example below will illustrate the amazing benefits of computer aided image processing in better understanding works of art.

The problem being explored here is a suspected signature on an oil painting. The 'signature' was first noticed using infrared reflectography but the technique did not reveal enough information to confirm if indeed what we saw was writing or just accidental brushstrokes the eye interpreted as writing. The principal difficulty was that the signature was actually painted over completely during a previous restoration and was thus rendered invisible.

The problem was solved by digitally scanning the suspected area in specular illumination. The idea was, that if there is indeed a signature hiding below the painted layer, the brushstrokes comprising it must have some thickness and may be detectable with sensitive analysis.


2. The image was first converted to grayscale and subjected Fast Fourier Transform analysis. Experiments revealed a band of frequencies corresponding to the average width of fine brushstrokes.	3. Once this band was identified it could be isolated and amplified. The result reveals what appear to be letters. For the first time the reading is proposed as 'Rosa'.

4. Removing 'noise' from the image confirms that indeed there is writing on the painting. Without much reservation it can now be safely interpreted as 'Rosa'.	5. Enhancing the contrast and further filtering confirm the earlier reading.

6. In this image a further test is made by using a tracing algorithm. Here, if the writing is coincidental the result would be garbled and would appear as the irregular patterns do around the writing.	7. The final image is a false-color rendering of the result of the trace. The name indeed reads 'Rosa' confirming the earlier attribution of the painting. Comparisons with the artist know signatures helped further the attribution and authentication process.

Only a few representative steps are actually described and illustrated here for reasons of brevity.
If you have any questions please write to Paul Biro