Nine-step ("EIA") charts have reflectance values arranged in an exponential relationship, r = 0.030 10^(0.18175 k), where k ranges 0 through 8. The reflectance steps correspond to uniform increments of optical density. These charts are typically called “logarithmic.”
Eleven-step ("ITE‑J") charts are designed to have reflectances that, when imaged by a video camera (having an OECF comparable to that standardized in BT.709), produce uniform video signal value increments. By convention, 11‑step charts have reflectance values r = 0.9 INVOECF709[0.100 + 0.090 k], where k ranges 0 through 10 and OECF709 symbolizes the BT.709 optoelectronic conversion (“gamma correction”) function.