imagesc pixels unaligned with x axis for certain data sizes

Hello,

I am using imagesc to plot data (a 2D FFT). I found that when my data size is greater than 1024 indices, the pixel size does not match the x axis. Things look fine at a size of [3 1000] and [3 1024] but out of phase at [3 1025] and [3 1251]. This started after my workstation was updated to Win11. Prior to that, things worked fine no matter what the data size.

What could be causing this and does anyone know what a fix could be?

xleng = 1251;
figure
imagesc(rand([3 xleng]))

Below is an image with xlen set to 1000, showing the pixels in phase with the x axis

Below is an image with xlen set to 1251, showing the pixels out of phase with the x axis

Finally, here is a clip of my 2DFFT dataset, showing how the pixel bins are out of phase with size [360 1251]

[DGM]

I can't replicate this, but I'm not running windows, so that really doesn't help much. I'm curious how this could be an environment issue.

xleng = 1251;
figure
imagesc(rand([3 xleng]))
xlim([1245 xleng])

[Charlie Black]

Yeah, when I try this on other PCs at my workplace (Win 10 and newly Win 11 machines) it works fine, and I get the result you showed. This is somehow unique to my install/machine.

FWIW, I get this when I run

xleng = 1251;
figure
imagesc(rand([3 xleng]))
xlim([1245 xleng])

[DGM]

This is grasping, but are you sure you don't have anything shadowing image() that might explain the slightly-off default XData?

Answer 1

[Ashok]

Hey @Charlie Black,

I could replicate the issue in R2021a but not in R2021b. Just a heads up, my current system runs Windows 11 and doesn't support hardware OpenGL.

Running the ‘opengl info’ command right after opening MATLAB gave these outputs:

R2021a:

R2021b:

As seen in the above images, the ‘HardwareSupportLevel’ is sometimes set to 'full' in R2021a even though the system doesn't support hardware OpenGL, leading to a similar issue.

Switching to software rendering by running the following command in the MATLAB command window seems to fix the rendering issue.

opengl software 

Alternatively, one can start MATLAB with software OpenGL selected by running ‘matlab -softwareopengl’ in the windows command line. To save software OpenGL for future sessions, use the following command in the MATLAB command window.

opengl('save', 'software') 

For more information on low-level graphics issues, check out this documentation page: 

https://www.mathworks.com/help/releases/R2021a/matlab/creating_plots/resolving-low-level-graphics-issues.html

[Charlie Black]

Thanks for digging into this! Very helpful. I will say, the issue seems to have resolved itself after I reinstalled GPU drivers. FWIW, here is my output for opengl info.

Version: '4.6.0 Compatibility Profile Context 22.20.20.06.231106'
                           Vendor: 'ATI Technologies Inc.'
                         Renderer: 'AMD Radeon RX 640'
            RendererDriverVersion: '31.0.12020.6006'
        RendererDriverReleaseDate: '06-Nov-2023'
                   MaxTextureSize: 16384
                           Visual: 'Visual 0x1a, (RGBA 32 bits (8 8 8 8), Z depth 16 bits, Hardware acceleration, Double buffer, Antialias 8 samples)'
                         Software: 'false'
             HardwareSupportLevel: 'full'
        SupportsGraphicsSmoothing: 1
    SupportsDepthPeelTransparency: 1
       SupportsAlignVertexCenters: 1
                       Extensions: {246×1 cell}
               MaxFrameBufferSize: 16384

Even with HardwareSupportLevel as Full, it still seems to work now. I am not sure what the root cause was initially, but if I ever run into problems again, I will try switching to software rendering. Interesting that 2021a will default to that even though it does not support it.

[Ashok]

Hey @Charlie Black,

Happy to know that the issue has been resolved and thanks for sharing the fix.