There are three ways to convert image files to different formats.
Converting in Houdini
From the File menu, click Import and choose Image.
Select an image and click the Open button.
This creates a file in a Compositing network.
Click the node and select Save Image.
Rename the file with the new format and click the Save button.
Converting in MPlay
You can do this my launching Image View from the Start menu in Windows, or through the Command Line Tools in Linux.
Select an image and click the Load button.
Choose Save Frame As from the File menu and rename the file with the new file format.
Converting with Command Line Tools
Open Command Line Tools from the Start Menu.
Go to the folder where your image is saved and type:
iconvert, followed by the name of your file, followed by the new name of your file.
iconvert butterfly.pic butterfly.rat
Press Enter to convert your file.
iconvert in the Command Line Tools and pressing Enter will show you the supported file formats.
iinfo in the Command Line Tools and pressing Enter will show you information about existing images in that folder.