System information (version)

• OpenCV => all
• Operating System / Platform => all
• Compiler => all

Detailed description

in truncate threshold example, the matplotlib did't show the correct image

image in tutorials
correct image

- for display the correct image, it shoud add the parameter vmin=0,vmax=255

Steps to reproduce

py tutorials markdown display issues

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