1. A method that assesses character-rendering quality, the method comprising: transmitting a test-character set of test characters to a character-rendering device for rendering; intercepting digital pixel-based character maps for the test characters of the test-character set, used by the character-rendering device for rendering the test characters, to serve as an input-character set of input characters; capturing, with a computing system, the test characters rendered by the character-rendering device to serve as an output-character set of output characters; for each input character, generating with the computing system, from the intercepted input characters, one or more first metrics that reflect differences between the input character and at least two of the input characters; for each output character, generating with the computing system, from the intercepted input characters and the captured output characters, one or more second metrics that reflect differences between the output character and at least two of the input characters; and outputting one or more indications of character-rendering quality based on the first and second metrics.