= Aerial-image modulation
<Aerial-image modulation> measures the variation of optical intensity in the image delivered to a <photoresist> before its chemical and development response. A common contrast measure is $M=(I_{\max}-I_{\min})/(I_{\max}+I_{\min})$, for nonnegative intensities with nonzero denominator. Equal bright and dark intensities give $M=0$; a dark minimum with a positive maximum gives $M=1$.
For example, intensities $9$ and $1$ give $M=0.8$. Multiplying both by the same exposure factor leaves $M$ unchanged, although it changes the deposited dose and can change the printed pattern. Image modulation and <photoresist contrast> therefore describe different stages of <photolithography>: the optical signal and the material's conversion of that signal into a developed profile.<Glossary of Lithography Terms by Chris A. Mack>[Aerial Image and Photoresist Contrast entries]{ref}
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