FreeType/TTF putText crashes with CV_32FC3 (low priority)

[cwreynolds]

System information (version)

• OpenCV => 4.5.0
• Operating System / Platform => macOS Catalina 10.15.7
• Compiler => Xcode 12.2

Detailed description

The older putText() function works on both CV_8UC3 and CV_32FC3 (probably all) types of Mat.

The version of putText() that uses FreeType2 and (e.g.) .ttf files appears to only work on CV_8UC3 Mats, according to the assert that fails while trying to put text on a 3xfloat Mat.

This seems easy enough to work around, so should be considered a low priority bug. But since I ran into it I thought I should file this report with code to reproduce.

Note that the documentation (here) does not mention the restriction to CV_8UC3.

Steps to reproduce

Run this function, passing in the pathname of a .ttf file:

void compare_putTexts(const std::string& ttf_pathname)
{
    auto two_putTexts = [&](const std::string& window, int type, int bright)
    {
        // Make white mat of given type.
        cv::Mat mat(300, 300, type, cv::Scalar::all(bright));
        // Draw text the original way.
        cv::putText(mat, "hello world", cv::Point(20, 100), cv::FONT_HERSHEY_SIMPLEX,
                    1, CV_RGB(0, 0, 0), 1, cv::LINE_AA);
        cv::namedWindow(window);
        cv::imshow(window, mat);
        cv::waitKey();
        // Draw text using TTF.
        cv::Ptr<cv::freetype::FreeType2> ft2;
        ft2 = cv::freetype::createFreeType2();
        ft2->loadFontData(ttf_pathname, 0);
        ft2->putText(mat, "hello world", cv::Point(20, 200),
                     30, CV_RGB(0, 0, 0), cv::FILLED, cv::LINE_AA, true);
        cv::imshow(window, mat);
        cv::waitKey();
    };
    two_putTexts("window 1", CV_8UC3, 255); // 3 x 8bit color
    two_putTexts("window 2", CV_32FC3, 1);  // 3 x float color
}

A window appears with text drawn by the old putText() on a CV_8UC3 Mat.
Type any key to proceed.
The window will show a second line of text using FreeType2.
Type any key to proceed.
A second window appears with a CV_32FC3 Mat.
Type any key to proceed.
Crashes with an assert failure:

terminating with uncaught exception of type cv::Exception: OpenCV(4.5.0) /tmp/opencv-20201123-26930-m95s1u/opencv-4.5.0/opencv_contrib/modules/freetype/src/freetype.cpp:197: error: (-215:Assertion failed) ( _img.empty() == false ) && ( _img.isMat() == true ) && ( _img.depth() == CV_8U ) && ( _img.dims() == 2 ) && ( _img.channels() == 3 ) in function 'putText'

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc

[alalek]

crashes

It is just an error with limitation messages in form of C++ exception.
Application crashes because it doesn't catch them.