With the continuing reduction of minimum feature sizes for semiconductor wafers, manufacturing tolerances for photomask CD errors were reduced proportionately. As a result, it has become increasingly important to separate the major sources of mask CD errors so that they can be quantified and appropriately addressed. In this article we describe a reliable, convenient and inexpensive technique for separating the blank, and process CD errors from the pattern generator CD errors using conventional market measurements on cross arrays and two-dimensional spatial advantage of the fact that the blank/process-induced CD error spatial distributions are known to be fixed relative to the mask blank, while the pattern generator CD error distributions are known to be fixed relative to the pattern generator, a spatial frequency domain analysis of multiple sets of CD measurements on the masks, each set printed by displacing the mask relative to the previous set, is shown to allow a simple and unambiguous separation of the two types of CD errors, These measurements also directly verify the expected result that the blank/process CD error contributors tend to have mainly low-spatial-frequency components, while the pattern generator tends to mainly have higher-spatial-frequency components. Furthermore, by utilizing this result, it is shown that a simple low-pass filter applied to a single set of market measurements provides a surprisingly accurate estimate of the relative sizes of these two error contributors. Results are presented from masks printed on two commercial mask-making systems, one optical and one e-beam.