Missing check for valid size of input images

[FlorianKordon]

Applying FROC to text line images that are too small (I didn't quantify the exact threshold) leads to different kinds of issues.

1. Within the NN, the pooling operation can break due to insufficient height/width.
2. ValueError during image resizing with pillow.

While providing proper image sizes might also be a responsibility of previous processors, an initial check for valid image dimensions before further processing in FROC might make sense.

I've attached two screenshots.

[kba]

Thanks for the report. I only wrote the OCR-D wrapper, this bug seems to be part of the implementation in froc.py, so you probably understand the code better than I do - can you provide a PR?

[bertsky]

I tend to side with @FlorianKordon that this is the OCR-D wrapper's responsibility. One could add a few checks prior to

ocrd_froc/ocrd_froc/processor.py

Line 164 in 42f1ce0

self._process_segment(line, line_image)

, skipping and logging a warning if the image is unsuitable. (We do have these checks in other processors, too.)