Exposure of Underdrawings in Oil Paintings Through

IR Analysis

Chad B. WeinerDr. Jon ArneyMay 8, 1998

Review - Underdrawings

Preparatory drawings applied directly to a ground and then covered by the oil painting.

Media used mostly charcoal pencil chalk

Review - IR Reflectography

Infrared radiation passes through the paint layer while being reflected by the charcoal substrate.

Aims of Research

To improve current IR underdrawing analysis techniques (Reflectography) using image processing methods.

To develop a means of removing the paint layer from the underdrawing using an equation derived from Kubelka-Munk theory.

Research Methodology

Samples - charcoal drawings sketched on a canvas & painted over by flake-white oil-based paint.

VIS images captured using a COHU camera.

IR images captured using a COHU camera covered by an Infrared filter.

Data Analysis

Preliminary analysis - IMLAB software. UD(i, j) = VIS(i, j) - IR(i, j)

Data Analysis

IR Image Subtraction

Programming

Visual Basic Program K, n -> variables

Results

Image Subtraction K=3.0 , n = 1.3

Results

IR K=3.0 , n = 1.3

Future Research Possibilities

Incorporate Kubelka-Munk Theory

Convert Grayscale Values from camera output into Reflectances

Determine the Absorption Coefficient Solve for the Ground Reflectance

(Underdrawing)

Conclusions

Unable to derive an equation from Kubelka-Munk Theory

Completed research provides enough evidence that it is possible to remove the paint layer and other artifacts from an underdrawing

The End