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?

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.

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.

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”.