Deficiencies under consideration that are correctable fall into two general categories - panel errors and matchline errors. Panel errors include inequality between panels of average panel brightness or color and also distribution of light and color within a panel. Matchline errors are not so simply divided into categories, which accounts in part for the extreme difficulty in controlling matchline appearance. These also involve distribution of light and color within the matchline area, but the matter is further complicated in the presence of even slight panel imbalance. In both panel and matchline errors, camera, printer and projector may be involved. Processing of negative and positive has been excluded at this time because the techniques used have made this a consideration too insignificant to be seen in the presence of other errors, although the characteristics of film do lead to certain kinds of trouble which can be controlled only with great difficulty and complexity. This will be discussed later.

    Considering first the irregularities that may occur within a single panel we find sources of error in all three pieces of equipment. Since in a single panel taken alone this type of error is generally of little consequence, it is also necessary to show how this affects a composite picture.