= Solution
On a graph of normalized remaining thickness against $\log_{10}D$, both <positive photoresist> curves remain near unity below $D_0$ and fall to zero by $D_c$. Their transition widths are $\log_{10}(D_c/D_0)=1/\gamma$: $0.752$ decades for the lower-contrast material and $0.177$ decades for the higher-contrast material. The latter therefore has a much steeper transition. The curves can be aligned at a common illustrative clearing dose; their absolute horizontal placement cannot be inferred from <photoresist contrast> alone.
The higher-contrast material distinguishes bright and dark regions even when <diffraction> has reduced their intensity modulation. The lower-contrast material requires a much stronger aerial-image modulation and loses small features earlier. Finite resist thickness, standing waves, acid <diffusion>, development conditions and photon statistics can limit actual performance beyond this threshold model.
\Image[/past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2019/paper-1-resist-contrast.png]
{title=Original normalized positive-resist contrast curves illustrating transition widths, with no assumed absolute sensitivity}
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