Calamari <ref xmlns="http://www.tei-c.org/ns/1.0" target="https://github.com/Calamari-OCR">(<hi rend="Internet_Link">https://github.com/Calamari-OCR</hi>)</ref>, also available under an open source license, implements a deep CNN-LSTM network structure instead of the shallow LSTM used by OCRopus. It yields superior recognition capabilities compared to OCRopus and Tesseract (Wick et al. 2018). Because of its Tensorflow backend it is possible to utilize GPUs in order to support very fast training and recognition. In addition, it supports the training of voting ensembles and pretraining, i.e. it uses an already existing model as a starting point instead of training from scratch.