It’s not possible to do imagesc and axis off at the same time.
However, you can modify the imagesc code to achieve this but you will not get MathWorks support for the modified version.
To avoid the graphical artifacts, try different figure renderers: painters, opengl, …
You can also try the startup flag -softwareopengl.
solved How to do imagesc and axis off at the same time in Matlab? [closed]