Recovering ancient Chinese records with multispectral imaging

The ghostly characters from over 2000 years ago revealed by the incredible effectiveness of MSI 

The challenge

The Western Zhou Dynasty, spanning the early-to-mid first millennium BCE, marks a critical stage in China’s early civilization. Its written records serve as a bridge connecting the past and present, allowing researchers to study the social structure, political system, cultural customs, and other aspects of that time. 

Written on thin strips of catalpa wood in red-orange vermilion, the characters once stood out starkly on the darker surface of the wood. 

Due to the ravages of environmental factors through the passage of time, the handwriting on the surface of the wooden slips has become difficult to identify. Faint traces can be seen with high-definition visible light capture, but they cannot be identified. 

Now, careful investigations that minimize contact can reveal this fading information – before it is lost forever.

Cinnabar’s spectral characteristics

Vermilion is made from cinnabar, a form of mercury sulfide. The spectral characteristics of cinnabar under infrared and ultraviolet light are not pronounced. Consequently, capturing individual images in infrared, infrared reflection, ultraviolet, and ultraviolet reflection does not yield good results. In such cases, images must be captured across the entire spectrum, followed by spectral analysis, interpretation, and annotation.

Fully automated capture process 

To quickly and easily produce images of the surface of the wooden strips, the Chinese researchers used MSI narrowband imaging with the Phase One Rainbow MSI Solution. 

Throughout the imaging process, there was no need for refocusing, re-alignment, or exposure correction for different spectral bands, as this is all fully automated in the Phase One MSI software. This can provide efficiency savings of up to 50 times compared to previous technologies and is a capability that other multispectral solutions cannot provide. 

Not limited to infrared and ultraviolet, the MSI solution can capture high-quality spectral information from 16 individual wavebands within the 365-940nm range. 

Read about the basics about MSI imaging.

Effective image reconstruction 

The analysis tools built into the MSI software, including Principal Component Analysis (PCA), Independent Component Analysis (ICA), and K-means Clustering, facilitate the immediate analysis of the narrowband image stacks, allowing researchers to find high-dimensional imaging results with significant contrast and difference for direct interpretation. 

Through PCA, the high-dimensional spectral data is reduced to several principal components, which can represent most of the information in the original data.  

After dimensionality reduction, the spectral feature differences between the handwriting and the background wood can be more easily identified, providing a basis for image clarification. 

Based on the results of PCA analysis combined with advanced image processing algorithms, the blurred handwriting contours are gradually restored. 

Further applications  

The successful imaging of these materials demonstrates the huge potential of modern technology in the preservation of cultural relics and research into them. 

Being able to interpret faint or blurred writing on wooden or bamboo with high quality opens up new possibilities for subsequent interpretation and research. Researchers now have the technical conditions for digital reexamination of unrecognizable information that was previously deemed difficult or inconvenient to collect. It is believed that the research and preservation of bamboo and wooden slips can be effectively furthered with the aid of AI image recognition technology. 

With historical collections including varied materials, different writing tools, and different causes of contamination and damage, Phase One’s MSI solution can deliver perfect image stacks quickly and efficiently, with no contact and no secondary damage to the original material.  

Moreover, the Phase One Rainbow MSI Solution provides high-quality, high-resolution images that can be used for subsequent purposes after the multispectral imaging itself, such as exhibitions and displays, allowing for both large-scale and detailed viewing.