  The key to detecting neutral hydrogen during the epoch of reionization (EoR)
is to separate the cosmological signal from the dominating foreground
radiation. We developed direct optimal mapping (DOM) to map interferometric
visibilities; it contains only linear operations, with full knowledge of point
spread functions from visibilities to images. Here, we demonstrate a fast
Fourier transform-based image power spectrum and its window functions computed
from the DOM images. We use noiseless simulation, based on the Hydrogen Epoch
of Reionization Array Phase I configuration, to study the image power spectrum
properties. The window functions show $<10^{-11}$ of the integrated power leaks
from the foreground-dominated region into the EoR window; the 2D and 1D power
spectra also verify the separation between the foregrounds and the EoR.
