A Japanese camera- Japanese is derived from the proper noun Japan.
This is not always the case:
Native Americans- Native is not derived from a proper noun, but is capitalised as the words together form the name of the group of people.
Ordinary adjectives that are not written with a capital letter are common adjectives.
Browse the following links to other content related to the term 'Proper Adjective' from the 'Adjectives and Adverbs' grammar category: