Image Comparison between Original and Duplicated Books on Goryeo History (高麗史) from 15th and 16th Centuries in Joseon Dynasty of Korea: Metal Type Prints vs. Re-engraved Woodblock Prints
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Abstract
In 1482, during the Joseon dynasty (조선, 朝鮮, 1392-1910), volumes of books on the history of the previous Goryeo dynasty (고려, 高麗, 918-1392) were written and printed with metal type. The similarities and differences between these books on the Goryeo history (고려사, 高麗史), printed with metal type in the 15th century and the identical book printed using re-engraved woodblocks in the 16th century were compared. The printed pages had the same width in both the metal printed books and woodblock books, but differences in page height were observed: the original metal printed books from the 15th century had larger heights than the woodblock printed books from the 16th century. Using image comparison and analysis between various versions of works of Goryeo history, we investigated the correlations between the directional shrinkage of the wood as a potential root cause of the size difference in only one direction between the metal type and the re-engraved woodblock-printed versions. It was confirmed that the comparison of the size and directions of the printed areas is a very effective method of determining the printing method and the sequence of changes in very similar versions of old Korean books.
1. INTRODUCTION
Korea is the country that invented movable metal type. Numerous books have been printed with metal type since the 13th century. Many old books printed with movable metal type remain. The world’s oldest extant metal printed b泉和尙頌證道歌), a designated Korean treasure in 2012 (Korea Heritage Service, 2024a; American Printing History Association, 2024; Yoo, 2022a; Yoo and Yun, 2024), printed in 1239. The second-oldest extant book is Jikji (Korean: 직지 or 백운화상초록불조직지심체요절, 直指 or 白雲和尙抄錄佛祖直指心體要節), printed at Heungdeoksa Temple (Korean: 흥덕사, 興德寺) in Cheongju (Korean: 청주, 淸州) of Korea in 1377 during the Goryeo dynasty (UNESCO, 2023a). Jikji was registered as a UNESCO Memory of the World on September 4, 2001, along with Gutenberg’s 42-line Bible printed in Germany in 1455.
Before the invention of metal type, printing was done with woodblocks. The Goryeo Daejanggyeong (고려대장경, 高麗大藏經, Goryeo dynasty Tripitaka), often referred to as the Tripitaka Koreana, is a Korean collection of the Tripitaka (Buddhist scriptures). It consists of 81,258 carved printing woodblocks from the 13th century, under commission by the Goryeo dynasty of Korea. It is currently stored at Haeinsa Monastery (해인사, 海印寺) in the southwest of Korea. It is often called the Palman Daejanggyeong (팔만대장경, 八萬大藏經, Eighty-thousand Tripitaka) due to the number of the carved printing woodblocks (UNESCO, 2023b; 2023c; Korea Heritage Service, 2024b).
Woodblock printing started long before the Tripitaka Koreana. The earliest technique for printing texts/documents, images, or patterns started in China and was used widely throughout East Asia. The earliest surviving printing examples on cloth from China date to before 220. Printed and painted gauze (Western Han Dynasty Length: 59 cm, width: 40 cm) has been unearthed from Xin Zhui(辛追)’s tomb in 1971 (Norman, 2024). Woodblock printing existed in the Tang Dynasty (唐) of China by the 7th century. It remained the most common East Asian method of printing books with texts and images until the 19th century. The world’s oldest surviving woodblock printed document is the Pure Light Dharani-sutra (무구정광대다라니경, 無垢淨光大陀羅尼經), a small Buddhist scroll (6.5∼6.7 cm wide and 620 cm long) discovered in 1966 at the Bulguksa Temple (불국사, 佛國寺) in Gyeongju (Korean: 경주, 慶州) in the southeast of Korea. Scholars have deduced that it was published under the Unified Silla (통일신라, 統一新羅) dynasty during 742∼751 (American Printing History Association, 2024; Korea Heritage Service, 2024c; 2024d, 1999; Sohn, 1959; 1971; Park, 2014).
One of the authors (W.S.Y.) previously reported a series of image comparisons and analysis results on six versions of nearly identical or very similar books called The Song of Enlightenment (南明泉和尙頌證道歌). He concluded that one particular version was the original metal type printed book in 1239 during the Goryeo dynasty (Yoo and Kim, 2021; Yoo, 2022a; 2022b; 2022c; 2022d; 2022e; 2022f; 2023a; 2024a; 2024b; Yoo and Yun, 2024). Quantitative characterization of dimensions, ink tones, and other characteristics of interest from photographed images has led to the discovery of the world’s oldest extant metal type printed book, 138 years older than Jikji and 216 years older than Gutenberg’s 42-line bible.
From a decade ago, digital humanities have become a very attractive and important research area for study of the history, archaeology, literature, bibliography, and so on. Systematic analysis of a very large number of digitized historical images, using deep learning (DL), has been proposed for the classification of printing technology used for digitized images of interest by a research group in Germany (Im et al., 2018; 2022). According to the research group, printing techniques and approximate printing periods can be identified through image analysis of digitized historical images. An international research group among Taiwan, Germany, and U.S.A. recently presented a novel approach for automatically classifying illustrations from historical Chinese local gazetteers using modern DL techniques (Chen et al., 2024).
In Korea, metal movable type was used to urgently print books and documents of various types in small quantities. When mass printing was necessary, woodblock printing was done based on handwritten documents and/or what had been printed with metal movable type. Metal type printing, woodblock printing and re-engraved woodblock printing were used together from the invention of metal type printing in 13th century until the introduction of modern printing methods using lead type, in the end of 19th century (Ok, 2013). The purpose of this study is to clarify the differences in printing methods by com-paring the images of old books with identical contents, printed with metal movable type and those printed with re-engraved woodblocks based on the previously printed books. It is important to establish a valid method for surmising the printing method and sequence of controversial old books for bibliographic and printing history research of old Korean and Asian documents and books of historic significance.
2. MATERIALS AND METHODS
2.1. Books of Goryeo history (高麗史) – Korean Treasure
Six sets of large volume books on Goryeo history (高麗史), printed in the Joseon dynasty (朝鮮, 1392-1910), have been designated as national treasures of Korea in 2021 (Table 1). Two sets of large volumes of books were printed with Eulhaeja metal type (乙亥字, metal types casted in 1455) in 1482. The two sets of large volumes of books were printed in 1613 using re-engraved woodblocks based on previously metal type printed books. An-other two sets of large volumes of books were printed between the 17th to 18th centuries using re-engraved woodblocks based on previous woodblock printed books. Among six sets of books designated as Korean treasure, two volumes were of the metal type printed books, printed in 1482, and two sets of the woodblock printed books printed in 1613 belonging to the collections of Kyujanggak (규장각, 奎章閣) Institute for Korean Studies (KIKS) of the Seoul National University of Korea.
Six sets of large volumes of books of Goryeo history (高麗史) designated as Korean treasure in 2021.
We compared and analyzed three book images (one metal printed book and two duplicated books printed using re-engraved woodblocks) of Goryeo history and from the collections of KIKS to investigate the similarities and differences between the metal type printed book and woodblock printed books in detail. Figure 1 shows a photograph of three books of Goryeo history printed in the Joseon dynasty. One book, on the top left, was printed using movable metal type in 1482. Two books on the top right and on the bottom were printed using re-engraved woodblocks in 1613, 131 years later. The exact woodblock copies of the metal type printed version were re-engraved for a large quantity of printing.
Three images of the first page of identical books of the history of the Goryeo dynasty of Korea (volume 1) for comparison. All three books are from the collections of Kyujanggak (奎章閣) Institute for Korean Studies (KIKS) of Seoul National University of Korea. ((a): metal type printed version in 1482, (b) and (c): duplicated woodblock printed version in 1618)
The two woodblock printed versions were stored in the historical archive sites of the Joseon dynasty at Taebaeksan Mountain and Odaesan Mountain before being transferred to the KIKS of Seoul National University of Korea. The books on the top right and the bottom were stored at the Taebaeksan Mountain and Odaesan Mountain historical archive sites, respectively. The handwritten statements and signature by a high-ranking civil servant (좌승지, 左承旨, the first secretary to the King of Joseon) by the family name of Lee (이, 李) who was in charge of historical archives on the woodblock printed books, verifies the year of printing (萬曆 四十一年九月, September 1613) and historical archival sites (Taebaeksan Mountain site (태백산사고, 太白山史庫) and Odaesan Mountain site (오대산사고, 五臺山史庫).
2.2. Image Analysis
Photographs with 150 dpi resolution taken using a digital camera (Nikon COOLPIX P310, Japan) were downloaded from the Korea Heritage Service website for image analysis and comparisons. The size of images was 4608 x 3456 pixels (Korea Heritage Service, 2024e).
Image comparisons and analyses of the photograph shown in Figure 1 were conducted using image analysis software (PicMan from WaferMasters, Inc., Dublin, CA, USA). The image analysis software, PicMan, was originally developed for automatic and quantitative analysis of varied types of digital images in semiconductors, materials science, and nanotechnology and now is actively applied in the new fields of the food industry, biology, medical research, colorimetric characterization of cultural heritage paintings and old historical documents and bibliographic research (National Research Institute of Cultural Heritage, 2022; Yoo et al., 2021; 2022; 2023).
PicMan has more automated functions specifically developed for easy image handling, selection, and quantitative analysis of features of interest compared to other commercial or open-source image editing/analysis software. In principle, the same image comparison and analysis can be achieved by combinations of other software such as Photoshop, Illustrator, Paint, Light-room, Image J, etc. However, the implementation and quantitative analysis for scientific reasoning becomes very complicated. It is very time-consuming to achieve the same results using combinations of multiple software. It often requires more than 10 times the effort for the same results. For these reasons, it is not highly recommended based on personal experience. This was the very reason to initiate the new software development project.
3. RESULTS
3.1. Background Paper Color Removal
An as taken photograph of three books shown in Figure 1 exhibit significant paper color difference between books printed using (a) metal type in 1482 and (b, c) re-engraved woodblock in 1613. The older book printed using metal type showed more brownish color. This may be due to the difference in traditional Korean Hanji paper (한지, 韓紙) and/or oxidation in air for a longer period of time,∼540 years since 1482. Due to the paper color difference between books, visual perception, and relative contrast are prone to be affected. To reduce this difference in first impression of the book, we have removed paper color from the as taken photograph.
Figure 2 shows the image of three books after paper color removal. Printed characters, handwritten characters with personal signature of a high-ranking civil in charge of historical archives in 1613 (∼410 years ago in Joseon dynasty of Korea) and stamped seals of collection institutions, including the Governor-General of Chōsen (Joseon) (조선총독부, 朝鮮總督府), Keijō Imperial University (경성제국대학, 京城帝國大學) under Japanese rule (1910∼1945) and Seoul National University (서울대학교) after the end of 19th century.
Three images of the first page of identical books of the history of the Goryeo dynasty of Korea (volume 1) after paper color removal for easy comparison. ((a): Metal type printed version in 1482, (b) and (c): Duplicated woodblock printed version in 1618).
3.2. Dimension Measurements
Vertical and horizontal dimensions of a printed rectangle on the page in each book are measured. While vertical dimensions (heights) of all three books differ, the horizontal dimensions (widths) are the same for all books (Figure 3). The height of (a) the metal type printed book was measured to be 212 mm and the heights of woodblock printed books were measured to be (b) 199 mm and (c) 195 mm. The height of woodblock printed books shrunk approximately 6.1% and 8.0% from that of the metal type printed book, respectively. The widths of all three books were measured to be 141 mm regardless of printing method used.
Three images of the first page of identical books of the history of the Goryeo dynasty of Korea (volume 1) after paper color removal for dimension measurement. Identical library seals stamped on the page can be used as references for relative size comparison and dimension measurements. ((a): Metal type printed version in 1482, (b) and (c): Du-plicated woodblock printed version in 1618)
All three books had two common seals stamped on. They are a 40 x 40 mm squared seal of the Governor-General of Chōsen (Joseon) and a 51 x 51 mm squared seal of the Seoul National University. The seal stamps can serve as ruler or dimensional reference. The sizes of two stamps on all three books were identical on the photograph as shown in Figure 3. Thus, the photograph under examination is not distorted and is valid for vertical and horizontal dimension measurement of all three books. Printing method dependence of printed dimensions can be studied using the measured dimensions of all three books. Directional shrinkage of woodblocks seemed to be responsible for the shrinkage of printed area in the vertical direction. A previous study also showed that the re-engraved woodblock printed books are smaller in the vertical direction than the original metal type printed version, even for the books printed in the same year (Yoo, 2022e).
3.3. Height and Width Comparisons
For easy height and width comparisons between books, the printed page of three books were stacked and shifted in horizontal and vertical directions. As seen in Figure 4, the vertical dimensions (heights) of printed pages differ between books while the horizontal dimensions (widths) are nearly identical, regardless of printing methods or books.
Three images of the first page of identical books of the history of the Goryeo dynasty of Korea (volume 1) for vertical and horizontal dimension comparison. ((a): vertical height comparison and (b): horizontal width comparison of three books printed with metal type and woodblock)
The metal type printed book has the largest printed area and height of all. For woodblock printed books printed in 1618, the height shrunk 6.1% and 8.0%, respectively, from the original metal printed book printed in 1482. One directional shrinkage of printed area and individual characters in woodblock printed books is common in old Korean books (Yoo, 2022e; 2022f; Shin, 2021). The origin of shrinkage in one direction in woodblock printed books will be discussed along with the woodcuts and shrinkage property as a function of moisture content (Peck, 1957; Canadian Woodworking & Home Improvement, 2006; Lee et al., 2015; Forest Product Laboratory, 2020; Yoo and Yun, 2024).
3.4. Image Comparisons of Handwritten Statements and Signatures
The two woodblock printed versions had handwritten statements and signatures of a high-ranking civil servant in charge of historical archives, as seen in Figure 5. The hand-written statement and signature on the top right book are intentionally colored red for highlighting purpose. It states that the book is supposed to be stored in the historical archival sites (Taebaeksan Mountain site (太白山史庫)). The statement was dated as September 1613 (萬曆 四十一年九月). The last name of the high-ranking official who wrote the statement was Lee (李). He wrote his official title (左承旨, the first secretary to the king of Joseon) and signed.
Image comparison of two handwritten notes and signatures inside the cover page of woodblock printed books. Three images of the first page of identical books of the history of the Goryeo dynasty of Korea (volume 1) are shown for comparison. ((a): Metal type printed version in 1482, (b) and (c): Duplicated woodblock printed version in 1618)
The same statement was written except for the name of the historical archival sites on the book below. The destination of the book was the Odaesan Mountain historical archival sites (五臺山史庫). For easy comparison, the red colored statement and signature was placed next to the one on the other book. The calligraphy font, location, and texture are almost identical, so it appears to have been written by the same person. The only difference between the two was the name of the historical archival sites: Taebaeksan Mountain site (太白山史庫) vs. Odaesan Mountain sites (五臺山史庫).
4. DISCUSSION
As indicated earlier, woodblock shrinkage due to the moisture content drop after re-engraving can result in dimensional change of woodblock printed area. It is important to understand wood shrinkage behaviors and possible impact on resulting woodblock prints (Yoo, 2022e; 2022f).
As the log is sawn and converted into boards to make woodblocks, water leaves the wood by evaporation from the surface. As water is evaporated at the surface, interior moisture migrates to the surface and the moisture content decreases by natural drying process (Peck, 1957; Forest Canadian Woodworking & Home Improvement, 2006; Lee et al., 2015; Product Laboratory, 2020). Wood shrinkage is caused by the evaporation of free water from freshly cut wood. The amount of water in wood fluctuates with the relative humidity of the environment. When the relative humidity increases, the wood expands, and when it decreases, the wood shrinks.
Until the moisture content gradually drops to 30% by weight compared to the dry weight of the wood, a fiber saturation point, there is no physical change in the size and shape of the board (or woodblock). Once the percentage of water content drops below 30%, the cell walls start to shrink and distortion of the piece of woodblock starts to occur as illustrated in Figure 6. The amount of shrinkage in a piece of wood is measured by volumetric shrinkage, which is the total shrinkage of the wood. The direction of the shrinkage is measured by radial and tangential shrinkage, which are the shrinkage that occurs on the wood’s thickness and width surfaces, respectively. The ratio of tangential shrinkage to radial shrinkage is called the T/R ratio, which is an indicator of the wood’s stability.
(a) Dimensional shrinkage of wood; (b) Relation between shrinkage and moisture content of wood (Moore, 2011).
The amount a wood species shrinks depends on the species and how it’s cut from the tree. Generally, wood shrinks more around its circumference (tangential shrinkage) than it does across its radius (radial shrinkage). The shrinkage along the annual growth rings (tangential shrinkage) is about twice as much as the shrinkage between the rings (tangential shrinkage). Shrinkage is not equal in both directions. Tangential shrinkage can vary from about 3% up to around 12%. Most woods fall in the range of about 6% to 10% tangential shrinkage. Radial shrinkage in solid wood can vary from less than 2% for some of the most stable wood species, upwards to around 8% for the least stable species. Most woods fall in the range of about 3% to 5% radial shrinkage. This unequal shrinkage causes distortion in a woodblock as it dries. The lengthwise shrinkage along the growth direction of tree (longitudinal shrinkage) is very small―typically about 0.1% to 0.2% (Peck, 1957; Canadian Woodworking & Home Improvement, 2006; Lee et al., 2015; Forest Product Laboratory, 2020; Shin, 2021; Moore, 2011; Yoo and Yun, 2024).
The printed height shrinkage of 6.1% and 8.0% in woodblock printed books compared to the metal type printed book agrees well with the tangential shrinkage of woodblocks (Figure 6). The difference between the two woodblock printed books can also be explained by the difference in their moisture content at the time of printing. Woodblocks can absorb moisture from the air which results in weight increase and woodblock distortion (swelling, enlargement, and/or twist). The woodblock distortion can also result in dimensional change in its printed area at the time of printing. The larger the woodblocks, the larger the distortion of woodblocks. Considering the size of woodblocks used for printing, the difference of 4∼5 mm in the height direction between woodblock prints seems to be very reasonable.
Similar shrinkage of re-engraved woodblock printed books in vertical direction compared to the original metal-type printed books was observed in a previous study on The Song of Enlightenment (南明泉和尙頌證道歌) printed between 13th and 16th centuries, Myeongeuirok (Korean: 명의록, 明義錄) printed in 1777 and Sok-Myeongeuirok (Korean: 속명 의록, 續明義錄) printed in 1778 (Yoo, 2022d; Yoo et al., 2023). The previous study on similar versions of old Buddhist books titled The Song of Enlightenment (南明泉和尙頌證道歌) and Jabidoryangchambeopjiphae (慈悲道場懺法集解) led to the discovery of the world’s oldest metal type printed book, printed in 1239 in the Goryeo dynasty of Korea (Yoo, 2022a; 2022b, 2022c; 2023a; 2024a; 2024b; 2024c; Yoo and Yun, 2024). One directional shrinkage of printed area in eleven re-engraved woodblock printed books from the Joseon dynasty has been reported in a PhD thesis in bibliography study (Shin, 2021). It agrees well with the result of this study.
5. CONCLUSIONS
We have investigated the volumes of books, Goryeo history (高麗史), on the history of the Goryeo dynasty (高麗, 918∼1392). It was originally written and printed with metal type in 1482, during the Joseon dynasty (朝鮮, 1392∼1910). The same books printed using re-engraved woodblocks in 1613 were also investigated and compared with the metal type printed book. The similarities and differences between the volumes of books of the Goryeo history, printed with metal type in the 15th century and re-engraved woodblocks in the 16th century of the Joseon dynasty were compared.
The dimensions of printed pages of various versions of the book were measured using image analysis software, PicMan. The width of the printed pages was found to be the same for both the metal type printed book and the re-engraved woodblock printed books. A remarkable difference of 6.1%∼8.0% in page height was measured between them. The original metal type printed book from the 15th century was the largest in height. The re-engraved woodblock printed books from the 16th century was smaller in height compared to the metal type printed book from previous century. There was also a noticeable difference (1.9%) in the height of printed pages between the woodblock printed books.
Through the image comparison and analysis between various versions of the old book of Goryeo history, we investigated and found the correlation between the directional shrinkage of wood was the likely root cause of the size difference in one direction (tangential direction along the circumference of age ring in woodblocks) between metal type and re-engraved woodblock printed versions. Comparison of the size and directions of printed areas is a very effective method for shedding light on the controversies regarding the printing method and sequence details on very similar versions of old Korean books.
The results of this study agrees well with previous reports on the world’s oldest metal type printed book, The Song of Enlightenment (南明泉和尙頌證道歌) printed in 1239 in the Goryeo dynasty of Korea and books printed using re-engraved woodblocks in following centuries. It also coincides with the metal type printed books (Myeongeuirok (明義錄) and Sok-Myeongeuirok (續明義錄)) and their re-engraved woodblock printed books in the same year as metal type printing in the 18th century of the Joseon dynasty of Korea.