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Posted by Dirk Alvermann on

Breaking the rules – the problem with concept writings

Release 1.10.1

Concept scripts are were used when a scribe quickly creates created a draft that is later on “written in the clean”. In the case of the Spruchakten, these are mainly the drafts to the judgments that were sent away later. The concept scripts were usually written very quickly and “sloppy”. Often letters are omitted or word endings “swallowed”. Even for humans conceptual writings are not easy to decipher  – for the machine they are a particular challenge.

To train an HTR model for reading concept scripts, you proceed in a similar way to training a model that is to interpret abbreviations. In both cases, the HTR model must be enabled to read something that is not really there – namely missing letters and syllables. To achieve this we must break our first rule: “We transcribe as ground truth only what is really written on paper”. Instead, we have to include all skipped letters and missing word endings etc. in our transcription. Otherwise we will not get a sensible and searchable HTR result in the end.

In our experiments with concept writings we tried at first to train special HTR models for concept scripts. The success was rather small. Finally, we decided to train concept scripts – similar to abbreviations – directly within our generic model. In doing so, we checked again and again whether the “wrong ground truth” that we produce in the process worsened the overall result of our HTR model. Surprisingly, the breaking of the transcription rule had no negative effect on the quality of the model. But this could also happen due to the sheer amount of ground truth used in our case (about 400,000 words).

HTR models are therefore able to distinguish concept writings from fair copies and interpret them accordingly – within certain limits. Below you can see a comparison of the HTR result with the GT for a typical concept script from our material.

Posted by Dirk Alvermann on

“between the lines” – Handling of inserts

At least as often as deletions or blackenings, there are overwritings or inserted text passages written between the lines. It is useful in two aspects to clarify at the beginning of a project how these cases should be handled.

In this simple example you can see how we handle such cases.

Since we include erasures and blackening in both layout and text, it is a logical step to treat overwrites and insertions in the same way. Usually, such passages are already provided with separate baselines during the automatic layout analysis. Every now and then you have to make corrections. In any case, each insertion is treated by us as a separate line and is also taken into account accordingly in the reading order.

Under no circumstances should you transcribe overwrites or insertions above the line instead of deletions. This would falsify the training material, even though the presentation of the text would of course be more pleasing to the human eye.

Posted by Dirk Alvermann on

Treatment of erasures and blackenings

HTR models treat erased text the same as any other. They know no difference and therefore always provide a reading result. In fact, they are amazingly good at it, and read useful content even where a transcriber would have given up long ago.

The simple example shows an erased text that is still legible to the human eye and which the HTR model has read almost without error.

Because we have already seen this ability of the HTR models in other projects, we decided from the beginning to transcribe as much of the erased and blacked out text as possible in order to use the potential of the HTR. The corresponding passages are simply tagged as text-style “strike through” in the text and thus remain recognizable for possible internal search operations.

If you don’t want to make this effort, you have the possibility to intervene in the layout at the corresponding text passages that contain erasures or blackenings and, for example, delete the baselines or shorten them accordingly. Then the HTR does not “see” such passages and cannot recognize them. But this is not less complex than the way we have chosen.

Under no circumstances should you work on erasures with the “popular” expression “[…]”. The transcribers know what the deletion sign means, but the HTR learns something completely wrong here, when many such passages come into training.

Posted by Elisabeth Heigl on


Release 1.9.1

Medieval and early modern manuscripts are usually full of abbreviations in all possible variations. These can be contractions (omission in the word) and suspensions (omission at the end of the word) as well as a wide variety of special characters. So if we want to transcribe old manuscripts, we must first consider how we want to reproduce the abbreviations: Do we reproduce everything as it appears in the text, or do we resolve everything – or do we adapt to the capacities of the HTR?

Basically there are three different ways to deal with abbreviations in Transkribus:

– You can try to reproduce abbreviation characters as Unicode characters. Many of the abbreviation characters used in 15th and 16th century Latin and German manuscripts can be found in the Unicode block “Latin Extended-D”. For special characters written in medieval latin texts, check the Medieval Unicolde Font Initiative. It depends entirely on the goals of your own project whether and when this path makes sense – it is quite complex anyhow.

– If you don’t want to work with Unicode characters, you could also use the “basic letter” of the abbreviation from the regular alphabet – like a literal transcription. Such a “placeholder” can then be provided with a textual tag that marks the word as an abbreviation (“abbrev”). How the tagged abbreviation is to be resolved can then be entered for each tag as “expansion”.

Thus the resolution of the abbreviation becomes part of the metadata. This approach offers the most possibilities for further use of the material. But it is also very laborious, because each and every abbreviation has to be tagged.

– Or you just dissolve the abbreviations. If you want to make large quantities of full text searchable, as we do, it makes sense to resolve the abbreviations consistently because it makes the search easier: Who is looking for “pfessores” instead of “professores”? We have made the experience that the HTR can handle abbreviations quite well; both the classic Latin and German abbreviations, as well as currency symbols or other special characters. This is why we resolve most abbreviations during transcription and use them as part of Ground Truth in HTR training.

The models we train have learned some abbreviations very well. The abbreviations frequently used in the manuscripts, such as the suffix “-en”, can be resolved by an HTR model – if it has been taught consistently.

But more complex abbreviations, especially the contractions, do cause difficulties for the HTR. In our project we have therefore decided to reproduce such abbreviations only in literal form.

In our Collection of Abbreviations we present the many different abbreviations that we find in our material from the 16th to 18th century. We also show how we (and later the HTR models) resolve them. This Collection will be updated by us from time to time – work in progress!

Posted by Elisabeth Heigl on

The more, the better – how to generate more and more GT?

Release 1.7.1

To make sure that the model can reproduce the content of the handwriting as accurately as possible, learning requires a lot of Ground Truth; the more, the better. But how do you get as much GT as possible?

It takes some time to produce a lot of GT. When we were at the beginning of our project and had no models available yet, it took us one hour to transcribe 1 to 2 pages. That’s an average of 150 to 350 words per hour.

Five months later, however, we had almost 250,000 words in training. We neither had a legion of transcribers nor did one person have to write GT day and night. Just the exponential improvement of the models themselves enabled us to produce more and more GT:

The more GT you invest, the better your model will be. The better your model reads, the easier it will be to write GT. You don’t have to write by yourself anymore, you just correct the HTR. With models that have an average error rate of less than 8%, we’ve produced about 6 pages of GT per hour.

The better the model reads, the more GT can be produced and the more GT there is, the better the model will be. What is the opposite of a vicious circle?

Posted by Elisabeth Heigl on

The more, the better – how much GT do I have to put in?

Release 1.7.1

As I said before: Ground Truth is the key factor when creating HTR models.

GT is the correct and machine-readable copy of the handwriting that the machine uses to learn to “read”. The more the machine can “practice”, the better it will be. The more Ground Truth we have, the lower the error rate.

Of course, the quantity always depends on the specific use case. If we work with a few, easy-to-read writing, little GT is usually enough to train a solid model. However, if the writings are very different because we are dealing with a large number of different writers, the effort will be higher. This means that in such cases we need to provide more GT to produce good HTR models.

In the Spruchakten we find many different writers. That’s why a lot of GT was created to train the models. Our HTR-models (Spruchakten_M_2-1 to 2-11) clearly show how quickly the error rate actually decreases if as much GT as possible is invested. We can roughly say that doubling the amount of GT in training (words in trainset) will halve the error rate (CER page) of the model.

In our examples we could observe that we have to train the models with at least 50,000 words of GT in order to get good results. With 100,000 words in training, you can already create excellent HTR models.

Posted by Elisabeth Heigl on

transcription guidelines

In the transcripts for the Ground Truth, the litteral or diplomatic transcription is used. This means that we do not regulate the characters in the transcription, if possible. The machine must learn from a transcription that is as accurate as possible so that it can later reproduce exactly what is written on the sheet. For example, we consequently adopt the vocal and consonant use of “u” and “v” of the original. You can get used to the “Vrtheill” (sentence) and the “Vniuersitet” (university) quite quickly.

We made only the following exceptions from the literal transcription and regulated characters. The handling of abbreviations is dealt with separately.

We cannot literally transcribe the so-called “long-s” (“ſ”) and the “final-s” because we are dependent on the antiqua sign system. Therefore we transfer both forms as “s”.

We reproduce umlauts as they appear. Diacritical signs are adopted, unless the modern sign system does not allow this; as in the case of the “a” with ‘diacritical e’, which becomes the “ä”. Diphthongs are replaced, for example the “æ″ becomes “ae″.

The Ypsilon is written in many manuscripts as “ÿ″. However, we usually transcribe it as a simple “y″. In clear cases, we differentiate between “y” and the similarly used “ij” in the transcription.

There are also some exceptions to the literal transcription with regard to the punctuation and special characters: In the manuscripts, brackets are represented in very different ways. But here we use the modern brackets (…) uniformly. The hyphenation at the end of the lines is indicated by different characters. We transcribe them exclusively with a “¬”. The common linkage sign in modern use – the hyphen – hardly occurs in the manuscripts. Instead, when two words are linked, we often find the “=”, which we reproduce with a simple hyphen.

We take the comma and point setting as it appears – if it exists at all. If the sentence does not end with a dot, we do not set a dot.

Upper and lower case will be adopted unchanged according to the original. However, it is not always possible to strictly distinguish between upper and lower case letters. This applies to a large extent to the D/d, the V/v and also the Z/z, regardless of the writer. In case of doubt, we compare the letter in question with its usual appearance in the text. In composites, capital letters can occur within a word – they are also transcribed accurately according to the original.

Posted by Elisabeth Heigl on

How to transcribe – Basic Decisions

In Transkribus, we create transcripts primarily to produce training material for our HTR-models; the so called „Ground Truth“. There are already a number of recommendations in the How-to’s for simple and advanced requirements.

We do not intend to create a critical edition. Nonetheless, we need some sort of guidelines, especially if we want to be successful in a team where several transcribers work on the same texts. Unlike classical edition guidelines, ours are not based on the needs of the scholarly reader. Instead, we focus on the needs of the ‘machine’ and the usability of the HTR result for a future full text search. We are well aware that this can only lead to a compromise in the result.

The training material should help the machine to recognize what we see as well. So it has to be accurate and not falsified by interpretation. This is the only way the machine can learn to read in the ‘right’ way. This principle is the priority and a kind of guideline for all our further decisions regarding transcriptions.

Many questions that are familiar to us from edition projects must also be decided here. In our project we generally use the literal or diplomatic transcription, meaning that we transcribe the characters exactly as we see them. This applies to the entire range of letters and punctuation marks. To give just an example: we don´t regulate the consonantal and vocal usage of the letters “v” and “u”. If the writer meant “und” (and) but wrote “vnndt”, we take it as literal and transcribe as the latter.

The perfection of the training data has a high priority for us. But there are also some other considerations influencing the creation of the GT. We would like to make the HTR results accessible via a full-text search. This means that a user must first phrase a word he is searching before receiving an answer. Since certain characters of the Kurrents font, such as the long „ſ“ (s) will hardly be part of a search term, we do regulate the transcription in such and similar cases.

In the case of sentence characters – using a certain amount of leeway here – we only regulate some. We regulate the bracket character for example, which is represented quite differently in the manuscripts. The same applies to word separators at the end of a line.

The usual “[…]” is never used for illegible passages. Instead this text area is tagged as “unclear”.