Hi, some applications can produce float32 depth maps in OpenEXR format and they can use Z channel instead of Y channel (but only Y is supported in OpenCV). And this is quite natural because Z channel is a "Distance of the front of a sample from the viewer" - see OpenEXR documentation.

Currently if you will try to read such float32 .exr image with single Z channel via imread(path, cv::IMREAD_UNCHANGED) - empty image will be returned.

The proposed fix will try to find Z channel only if no Y channel is found (i.e. this fix is backwards compatible).

Pull Request Readiness Checklist

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• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake