Version 1.12.0

As you have probably noticed, since last summer there is a second recognition engine available in Transkribus besides HTR+ – PyLaia. (link)

We have been experimenting with PyLaia models in the last weeks and would like to document our first impressions and experiences about the different aspects of HTR+ and PyLaia. First of all: considering the economic point of view, PyLaia is definitely a little bit cheaper than HTR+, as you can see on the price list of the Read Coop. Does cheaper also mean worse? – Definitely not! In terms of accuracy rate PyLaia can easily compete with HTR+. It is often slightly better. The following graphic compares an HTR+ and a PyLaia model trained with identical ground truth (approx. 600,000 words) under the same conditions (from the scratch). The performance with and without the Language Model is compared.

Perhaps the most notable difference is that the results of PyLaia models cannot be improved as much by using a Language Model as is the case with HTR+. This is not necessarily a disadvantage, but rather indicates a high basic reliability of these models. In other words: PyLaia does not necessarily need a Language Model to achieve very good results.

There is also an area where PyLaia performs worse than HTR+. PyLaia has more difficulties to read “curved” lines correctly. For vertical text lines the result is even worse.

In training PyLaia is a bit slower than HTR+, which means that the training takes longer. On the other hand, PyLaia is much faster in “acceleration”. It needs relatively few training epochs or iterations to achieve good results. You can compare this quite well with the two learning curves.

Our observations are of course not exhaustive. So far they only refer to generic models that have been trained with a high level of ground truth. Overall we have the impression that PyLaia can fully exploit its advantages with such large generic models.

Release 1.12.0

Since version 1.12.0 it is possible to train PyLaia models in Transkribus besides the proven HTR+ models. We have gained some experience with this in the last months and are quite impressed by the performance of the models.

PyLaia models can be trained like HTR or HTR+ models using the usual training tool. But there are some differences.

Like a normal HTR+ model you have to enter the name of the model, a description and the languages the model can be used for. Unlike the training of HTR+ models, the number of iterations (epochs) is limited to 250. This is sufficient in our experience. You can also train PyLaia models with base models, i.e. you can design longer training series that are based on each other. In contrast to the usual training, PyLaia has an “Early Stopping” setting. It determines when the training can be stopped, if a good result is achieved. At the beginning of your training attempts you should always set this value to the same number of iterations as you have chosen for the whole training. So if you train with 250 epochs, the setting for “Early Stopping” should be the same. Otherwise you risk that the training will be stopped too early.

The most important difference is that in PyLaia Training you can choose whether you want to train with the original images or with compressed images. Our recommendation is: train with compressed images. The PyLaia training with original images can take weeks in the worst case (with a correspondingly large amount of GT). With compressed images a PyLaia training is finished within hours or days (if you train with about 500.000 words).

Tips & Tools
For more detailed information, especially for setting specific training parameters, we recommend the tutorial by Annemieke Romein and the READ Coop guidelines.