Several GML file types exist that could be exported to a simple BMP image. Generally speaking, such export is good for viewing and sharing but does not contain any of the original data, just their visualization.
Convert Geography Markup Language to Standard Windows bitmap image.
We found one software available in the database for this conversion.
Microsoft Windows software - convert gml to bmp on Windows
A converter that is able to transform various GIS file formats
Convert from gml 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.