Black artifacts with modulate

[Andy]

Looks indeed similar.
Strangely i don't have the problem when i use his example image. :/

http://s8.postimg.org/izkvrqgph/c5cdc3e ... b8c0e2.jpg

[Andy]

Has anyone more ideas how to debug this? It's really a dealbreaker for me.

[dlemstra]

Did you build ImageMagick with OpenCL enabled? Maybe this is an OpenCL issue.

[Andy]

Yes i did.
I posted my build options here: https://www.imagemagick.org/discourse-s ... 50#p130289

Is imagemagick fully functional without opencl? I could build it without it then.

[Andy]

ok, reporting back.

With "--disable-opencl" the problem is gone!

Can someone explain to me what exactly opencl does and if i should report this somewhere?

[fmw42]

See http://www.imagemagick.org/script/archi ... istributed. Apparently IM automatically uses the GPU if available and OpenCL is enabled to process images faster than the CPU for certain IM functions. OpenCL must not work well on your platform/GPU or is buggy for whatever function you were trying to use or interfered with the processing of other functions.

[Andy]

Thx

[fmw42]

Indeed, https://github.com/ImageMagick/ImageMag ... celerate.c shows that -modulate is one of the functions that is accelerated by OpenCL

[Andy]

Not sure why this is happening tho. I am using the proprietary nvidia drivers on Linux. At least performance wise the best you can get on this platform.

[fmw42]

I have heard that certain OS do not handle OpenCL well, but I know little more than that. One of the IM developers would have to comment further.

[Andy]

Well, as far as i am concerned my problem is fixed but i am glad to help debuging this further.
Any suggestions how to get a dev in this thread?

[fmw42]

They will see it. dlemstra was the one that suggested to turn off opencl.

[dlemstra]

I suspect this is an issue with the OpenCL software on your operating system. I also have an OpenCL enabled build and I cannot reproduce the issue. I will forward this post to an OpenCL export and ask if they can reproduce this on their system. It might take a while before you have an answer. For now you are probably better of with disabling OpenCL on your system.

[fmw42]

Dirk,

Would they not have to have his exact OS and GPU card to have a chance of reproducing the error?

[dlemstra]

If it is a bug in the OpenCL driver we cannot fix it but maybe this is a bug in our OpenCL code. Just want to make sure its not the latter first.