Basic Information

tesseract 5.3.0-19-ga3b9ac, compiled with --disable-legacy

Operating System

macOS 13 Ventura

Compiler

clang 14.0

Current Behavior

When Tesseract is compiled with --disable-legacy, hOCR output reports each line as being upside-down (textangle 180) and omits baseline information.

Steps to reproduce:

./configure --disable-legacy
./tesseract some-image.jpg output hocr

In the generated output.hocr file, ocr_line entries look like this:

<span class='ocr_line' id='line_1_142' title="bbox 1334 3054 2119 3088; textangle 180; x_size 34; x_descenders 8; x_ascenders 9">

Expected Behavior

If orientation information isn't available I'd expect the image to always be treated as if it were page-up. So entries should look like this:

<span class='ocr_line' id='line_1_142' title="bbox 1334 3054 2119 3088; baseline 0 -8; x_size 34; x_descenders 8; x_ascenders 9">

Suggested Fix

Internally, it looks like the issue is that:

1. ColumnFinder::text_rotation_ is initialized to a null vector. When the legacy engine is disabled, the ColumnFinder::CorrectOrientation function does not get called, and so this vector remains null.
2. This null vector gets propagated to PageIterator::Orientation, which does not handle this case correctly, as it converts this null vector to ORIENTATION_PAGE_DOWN -

   tesseract/src/ccmain/pageiterator.cpp

   Line 585 in a3b9acf

   if (up_in_image.y() > 0.0F) {

3. The HOCR renderer then maps this orientation value to textangle 180 and omits baseline info

Some fixes I tested locally were to change the initialization of ColumnFinder::text_rotation_ to be the same as the norotation value in ColumnFinder::CorrectOrientation, or to change the logic in PageIterator::Orientation to handle null rotation vectors by mapping them to ORIENTATION_PAGE_UP. I'm happy to submit a PR but I'm not sure the preferred way to go.