The invention relates generally to methods of monitoring and controlling the processing of blood and blood samples, particularly the separation of blood and blood samples into its components. In one aspect, the invention relates to optical methods, devices and device components for measuring two-dimensional distributions of transmitted light intensities, scattered light intensities or both from a separation chamber of a density centrifuge. In embodiment, two-dimensional distributions of transmitted light intensities, scattered light intensities or both measured by the methods of the present invention comprise images of a separation chamber or component thereof, such as an optical cell of a separation chamber. In another aspect, the present invention relates to multifunctional monitoring and control systems for blood processing, particularly blood processing via density centrifugation. Feedback control systems are provided wherein two-dimensional distributions of transmitted light intensities, scattered light intensities or both are measured, processed in real time and are used as the basis of output signals for controlling blood processing. In another aspect, optical cells and methods of using optical cells for monitoring and control blood processing are provided.