Art Master - is the easiest graphic viewer and converter for Mac. It’s Drag and Drop based so you can just drop your graphic without extra clicking and selecting.
A simple controls toolbar with most essential tools are built right in.
Zoom to fit, zoom in, zoom out.
PSD, JPEG, JPG, PNG, GIF, TIFF, BMP.
Save graphics in other formats like PDF, PNG, JPG, JPEG or TIFF.