Vertical writing systems are not handled correctly in gImageReader

[lhy7889678]

Vertical writing systems can be OCRed (fairly) reliably with the tesseract command-line tool, but will get garbled characters with gImageReader by default. Horizontal writing systems are not affected.

Here are some sample images (in chi_sim, jpn, chi_sim_vert, jpn_vert respectively):

Here are the results using tesseract:

(縦組み is not OCRed correctly, but that is not a big problem.)

Here is the result using gImageReader (taking jpn_vert as an example):

I noticed that after rotating the image 90° counterclockwise, the result will be correct:

(and 縦組み is OCRed correctly!)

The issue has been reported in Issue #552, but it is mistakenly regarded as a bug in tessdata. Since the tesseract command-line tool can handle it correctly, it is definitely gImageReader's fault.

I'm using gImageReader 3.4.2 and tesseract 5.4.1 under Arch Linux, using the default tessdata provided by tesseract. I noticed that gImageReader says it is using tesseract 5.3.4 in the "About" dialog, so this might have something to do with the problem.

[manisandro]

Does it help to select this page segmentation option:

?

[lhy7889678]

Does it help to select this page segmentation option: [...]?

Yes, "Assume single block of vertically aligned text" works for me. On the other hand, both "Automatic page segmentation" and "Page segmentation with orientation and script detection" fail in this situation.

However, I did another experiment. When there are multiple lines, both "Automatic page segmentation" and "Page segmentation with orientation and script detection" work out of the box. Here is a sample image in Chinese:

The tesseract command-line tool can handle both single-line case and multiple-line case correctly without any tweaks (except for a few misrecognized characters).

PS: The sample text is a Chinese version of "Lorem ipsum". The original text is

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[manisandro]

One would need to check the tesseract executable source code to figure out how it configures the engine.