Text recognition crnn

[LaurentBerger]

new c++ sample https://github.com/opencv/opencv_zoo/tree/main/models/text_recognition_crnn

[WanliZhong]

@LaurentBerger Hi, thanks for contribution, this PR need to update readme document.

[WanliZhong]

Thanks for your contribution!👍👍👍, here are something I think need to be modified.

[WanliZhong]

need to use -i=/path/to/image or --input=/path/to/image

[WanliZhong]

using -v flag can't show the image

[LaurentBerger]

./build/opencv_zoo_text_recognition_crnn -v=0
show result as text but won't stop without ctrl+c. Must I add a counter to stop after 100 inferences?

[WanliZhong]

I think just be as consistent as possible with other demos

[fengyuentau]

using -v flag can't show the image

Just modify the doc here to make sure the commands work. It does not worth making 100% same behavior as Python demos.

[WanliZhong]

this command can't recognize from camera.

[fengyuentau]

--charset=charset_3944_CN.txt I dont see we have this file in this pull request.

[LaurentBerger]

May be there is something I don't understand : in readme

Selected model must match with the charset:

    Try text_recognition_CRNN_EN_2021sep.onnx with charset_36_EN.txt.
    Try text_recognition_CRNN_CH_2021sep.onnx with charset_94_CH.txt
    Try text_recognition_CRNN_CN_2021sep.onnx with charset_3944_CN.txt.

Then i understand that model gives charset to use then in code I use those line

        if (this->modelPath.find("_EN_") != string::npos)
            this->charset = loadCharset("CHARSET_EN_36");
        else if (this->modelPath.find("_CH_") != string::npos)
            this->charset = loadCharset("CHARSET_CH_94");
        else if (this->modelPath.find("_CN_") != string::npos)
            this->charset = loadCharset("CHARSET_CN_3944");
        else
        {
            CV_Error(-1, "Charset not supported! Exiting ...");

        }

[fengyuentau]

We integrated charset characters into the class wrapper crnn.py from separate files, but forgot to update the information in readme. So the current readme is outdated, you might update in this pull request as well.

[fengyuentau]

LGTM 👍