In art, an underpainting is an initial layer of paint applied to a ground, which serves as a base for subsequent layers of paint. Underpaintings are often monochromatic and help to define colour values for later painting.

underpainting
Underpainting
Underpainting Recovery using Synchrotron-based X-ray Fluorescence Imaging Data
Virtual underpainting reconstruction from X-ray fluorescence imaging data
F-68 Visualizing the 17th Century Underpainting Using Mobile and Synchrotron-Based Scanning Macro-XRF
The Use of Digital Image Processing to Clarify the Radiography of Underpainting
Visualizing the 17th century underpainting in Portrait of an Old Man by Rembrandt van Rijn using synchrotron-based scanning macro-XRF
Attenuating hue identification and color estimation for underpainting reconstruction from x-ray synchrotron imaging data
Attenuating hue identification and color estimation for underpainting reconstruction from x-ray synchrotron imaging data
文學的政治底稿 : 英美文學史論集 : The political underpainting : essays in the cultural history of Anglo-American literature