OpenCV 4.7 C++17 Windows 10 - imread warn cutoff, empty return

C++
1

When attempting to open a jpg or png with imread, I always get the same WARN, and then it fails to load the image.

The error is cutoff compared to all the other errors I see when I search (I got an error about imwrite command help for example).

It goes:
[ WARN 0@0.840] global loadsave.cpp:244 cv::findDecoder imread_('
…with no filename at all.

I explicitly check that the file exists with the C++17 std::filesystem::exists() func, with the file path (roughly) declared as:
const String image_path = String("C:/Users/user/repository/image.jpg")'

Then, I just call it like:
Mat image = imread(image_path, IMREAD_UNCHANGED);
It then returns an empty Mat object.

What may be causing this error?

2

please try to debug this …

3

It could be caused by a faulty image file, perhaps an empty file, where the file format signature is not recognized by the recognizers (see the code).

4

this is ‘idealized’ (so no problem)

please show real world data / filenames, that make this happen !

6

I found an image on Google that I can share for this test (from https://ecdn.teacherspayteachers.com/thumbitem/2D-Shapes-Poster-4602583-1559330790/original-4602583-1.jpg).

I renamed the file to shapes-color.jpg, reflected that in the code, and get the same error.

7

I took a look at that code, and it is part of what confuses me. Why would the warning log prematurely end while trying to read in my filename?

I am attempting to get Visual Studio to comply and let me set a breakpoint in or step into imread, but I am not having any luck.

8

you need a DEBUG build of the opencv libs for that.

this is indeed the most interesting question here !

is there any chance, you made a mess in your VS project ?
opencv actually only requires c++11. what happens, if you restrict it to that (instead of c++17) ?

9

It is especially bizarre…

I even just now attempted to emulate the source code exactly by doing:

FILE* f = fopen(filename.c_str(), "rb");
if (f) {
    cout << "Opened file just fine!" << endl;
}

This opened a handle to the file just fine.

Reverting my Visual Studio 2022 to C++14 still has the same error…and I’m not a fan of the idea of trying to install an old Visual Studio to test C++11.

10

understood …

btw, i don’t think, it’s anything about the image data (code does not get that far …)

that at least means, your compiler isn’t broken :wink:
however, something horrible seems to happen to same code deep inside imgcodecs .

12

There is not like some separate image processing libraries I need to install that are not present in the 4.7 installer on the website, is there?

I installed only this (https://github.com/opencv/opencv/releases/download/4.7.0/opencv-4.7.0-windows.exe) and cmake.

I setup Visual Studio following this tutorial as closely as I could: How to install OpenCV for C in Windows.