In some cases the user wants to specify the compose_megapix parameter if the resulting image size should be limited.

This causes "compose_scale" to be different than 1

without rounding the composed image sizes (variable "sz") which are calculated by full_img_sizes[i][0] * compose_scale they will be odly fractions of a pixel (e.g. (5300.965, 3772.897)) and therefore cause a "TypeError: integer argument expected, got float" in line

456 roi = warper.warpRoi(sz, K, cameras[i].R)

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• 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