  We introduce a novel and uniform framework for quantum pixel representations
that overarches many of the most popular representations proposed in the recent
literature, such as (I)FRQI, (I)NEQR, MCRQI, and (I)NCQI. The proposed QPIXL
framework results in more efficient circuit implementations and significantly
reduces the gate complexity for all considered quantum pixel representations.
Our method only requires a linear number of gates in terms of the number of
pixels and does not use ancilla qubits. Furthermore, the circuits only consist
of Ry gates and CNOT gates making them practical in the NISQ era. Additionally,
we propose a circuit and image compression algorithm that is shown to be highly
effective, being able to reduce the necessary gates to prepare an FRQI state
for example scientific images by up to 90% without sacrificing image quality.
Our algorithms are made publicly available as part of QPIXL++, a Quantum Image
Pixel Library.
