# Image to Text
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**WARNING**: This example is based on the [legacy version of OpenNMT-py](https://github.com/OpenNMT/OpenNMT-py/tree/legacy)!
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A deep learning-based approach to learning the image-to-text conversion, built on top of the OpenNMT system. It is completely data-driven, hence can be used for a variety of image-to-text problems, such as image captioning, optical character recognition and LaTeX decompilation.
Take LaTeX decompilation as an example, given a formula image:
![](http://lstm.seas.harvard.edu/latex/results/website/images/119b93a445-orig.png)
The goal is to infer the LaTeX source that can be compiled to such an image:
```
d s _ { 1 1 } ^ { 2 } = d x ^ { + } d x ^ { - } + l _ { p } ^ { 9 } \frac { p _ { - } } { r ^ { 7 } } \delta ( x ^ { - } ) d x ^ { - } d x ^ { - } + d x _ { 1 } ^ { 2 } + \; \cdots \; + d x _ { 9 } ^ { 2 }
```
The paper [[What You Get Is What You See: A Visual Markup Decompiler]](https://arxiv.org/pdf/1609.04938.pdf) provides more technical details of this model.
### Dependencies
* `torchvision`: `conda install torchvision`
* `Pillow`: `pip install Pillow`
### Quick Start
To get started, we provide a toy Math-to-LaTex example. We assume that the working directory is `OpenNMT-py` throughout this document.
Im2Text consists of four commands:
0) Download the data.
```bash
wget -O data/im2text.tgz http://lstm.seas.harvard.edu/latex/im2text_small.tgz; tar zxf data/im2text.tgz -C data/
```
1) Preprocess the data.
```bash
onmt_preprocess -data_type img \
-src_dir data/im2text/images/ \
-train_src data/im2text/src-train.txt \
-train_tgt data/im2text/tgt-train.txt -valid_src data/im2text/src-val.txt \
-valid_tgt data/im2text/tgt-val.txt -save_data data/im2text/demo \
-tgt_seq_length 150 \
-tgt_words_min_frequency 2 \
-shard_size 500 \
-image_channel_size 1
```
2) Train the model.
```bash
onmt_train -model_type img \
-data data/im2text/demo \
-save_model demo-model \
-gpu_ranks 0 \
-batch_size 20 \
-max_grad_norm 20 \
-learning_rate 0.1 \
-word_vec_size 80 \
-encoder_type brnn \
-image_channel_size 1
```
3) Translate the images.
```bash
onmt_translate -data_type img \
-model demo-model_acc_x_ppl_x_e13.pt \
-src_dir data/im2text/images \
-src data/im2text/src-test.txt \
-output pred.txt \
-max_length 150 \
-beam_size 5 \
-gpu 0 \
-verbose
```
The above dataset is sampled from the [im2latex-100k-dataset](http://lstm.seas.harvard.edu/latex/im2text.tgz). We provide a trained model [[link]](http://lstm.seas.harvard.edu/latex/py-model.pt) on this dataset.
### Options
* `-src_dir`: The directory containing the images.
* `-train_tgt`: The file storing the tokenized labels, one label per line. It shall look like:
```
...
...
...
...
```
* `-train_src`: The file storing the paths of the images (relative to `src_dir`).
```
...
```