Generally speaking, graphics patterns used in various editors like Photoshop, GIMP or similar are images themself so there should be no problem in converting such patterns to formats like IMG. Can be done using various graphics converters.
Convert Gimp pattern file to Bitmap picture.
We have found one software suitable in our database for this conversion.
Multiplatform software - convert pat to img on any platform
Cross-platform batch image transcoder compatible with 500 picture image formats
Convert from pat file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.