Maximum supported image size

[MerlijnWajer]

Environment

• Tesseract Version: 4.1.1 and latest master
• Platform: Linux gentoo-x230 5.6.18-grsec #2 SMP Tue Jul 7 18:17:17 CEST 2020 x86_64 Intel(R) Core(TM) i5-3320M CPU @ 2.60GHz GenuineIntel GNU/Linux

Current Behavior:

On large images, Tesseract fails like this:

Tesseract Open Source OCR Engine v4.1.1 with Leptonica
Warning: Invalid resolution 0 dpi. Using 70 instead.
Image too large: (2559, 37192)
Error during processing.

This is the image in question (large image!):
https://archive.org/download/manualzz-id-765154/765154_jp2.zip/765154_jp2/765154_0017.jp2

Expected Behavior:

Tesseract would process the image without erroring out.

Comments

I don't know where exactly this limitation comes from. I see that the specific error comes from the Otsu thresholding code, but I am not sure if the limit of 2^15 (INT16_MAX) limit is actually also a leptonica maximum size limit.

Perhaps this is not considered a problem and the bug can be closed, but as it stands I am not sure what the best practice would be to OCR the image linked above. Perhaps the limit can be raised some, to 2^16 ?

[stweil]

@MerlijnWajer, did you replace the image? I just loaded the image from the URL above, and it works because the size is 1706 x 24795 which is supported by the current tesseract.

Leptonica uses l_int32 for image dimensions.

[MerlijnWajer]

Yes, unfortunately someone changed the image to make it work for the existing item I linked to. I'll try to provide another sample file.

[MerlijnWajer]

Here's another example:

https://wizzup.org/সহজ_কুরআন_শিক্ষা_0005.jp2

[amitdo]

tesseract/src/ccmain/thresholder.cpp

Lines 188 to 192 in 8b0c540

	bool ImageThresholder::ThresholdToPix(PageSegMode pageseg_mode, Pix **pix) {
	if (image_width_ > INT16_MAX || image_height_ > INT16_MAX) {
	tprintf("Image too large: (%d, %d)\n", image_width_, image_height_);
	return false;
	}

[MerlijnWajer]

It looks like with 57b79742920cdda6d72e4fd7d0cab218db22f08b this limit is removed, and now the output is:

$ tesseract -c thresholding_method=2 /tmp/সহজ_কুরআন_শিক্ষা_0005.jp2 -
terminate called after throwing an instance of 'std::length_error'
  what():  cannot create std::vector larger than max_size()

[stweil]

Several Tesseract classes are currently limited to images with a maximum width and heigth of 32767 (INT16_MAX) because they use int16_t coordinates. Here is a list of classes identified so far:

TPOINT, BLOCK, PDBLK, ICOORD, ICOORDELT, TBOX, OL_BUCKETS

For some of those it might be possible to replace int16_t by uint16_t which would raise the limit for image dimensions to 65535, but some also use negative values. So maybe we have to use int32_t (which is compatible with Leptonica).

[stweil]

@MerlijnWajer, if you want you can test pull request #3435 for your large images. I still don't consider that as stable code, so would not use it for production of normal sized images.

[MerlijnWajer]

Great! I'll try to do this next week.