New Post: Strange Artifacts in Caption CMYK Image

I think I came to a solution: convert the image to RGB and after to CMYK, hope this don't change anything when print.

Based on docs I did this:

'Convert do RGB
image.AddProfile(ColorProfile.SRGB)

'Write file
image.write(Server.MapPath("file.jpg"))

'Read and write CMYK file
dim cmykConverter As new MagickImage(Server.MapPath("file.jpg"))
cmykConverter.AddProfile(ColorProfile.USWebCoatedSWOP)
cmykConverter.write(Server.MapPath("file.jpg"))

I tried many things to understand why these artifacts show up but I don't came to any solid conclusion, this remembers me a GPU problem in games.
I'm out of time too, so for now this is working.