Measuring light intensity from a photograph: Comment on “Using a shoebox spectrograph to investigate the differences between reflection and emission” by Timothy T. Grove, Jacob Millspaw, Eric Tomek, Rebeca Manns, and Mark Masters [Am. J. Phys. 86<

Editor's Note: This brief Comment points out that a previous paper was erroneous in claiming that the JPG black-and-white-format output is linear in light intensity. While that error does not affect the usefulness of the previous paper, the Comment may prevent readers from making mistakes in other work with images.