An imager tile comprising: an array of sub-imager pixel arrays, the sub-imager pixel arrays arranged in rows and columns; each of the sub-imager pixel arrays including a plurality of four-side buttable imager pixels distributed on a wafer substrate (132,133) and an on-chip digitizing electronic readout circuit comprising readout electronics; each of the four-side buttable imager pixels including at least one photodiode configured to be exposed to incident photon radiation; a plurality of pixel groupings formed from among the plurality of imager pixels; the readout electronics including a buffer amplifier for each of the plurality of pixel groupings and the inputs of the buffer amplifier connected to respective outputs of each four-side buttable imager pixel of the pixel grouping; each of the sub-imager pixel arrays further including: a plurality of shared analog front ends (220,222,224,226), the inputs of each shared analog front end connected to respective outputs of multiple buffer amplifiers from among the plurality of pixel groupings; an analog-to-digital converter located at a common centroid location relative to the plurality of shared analog front ends, a sub-imager select I/O line to individually select an output from each of the plurality of shared analog front ends as an input for the analog-to-digital converter; the analog-to-digital converter having a clock input line, and a shared digital output line that is shared among the respective multiple buffer amplifiers; and wherein a pixel is individually addressable by data provided on the sub-imager select I/O line, and the respective digitized pixel output is provided on the shared digital output line via the respective buffer amplifier. an array of sub-imager pixel arrays, the sub-imager pixel arrays arranged in rows and columns; each of the sub-imager pixel arrays including a plurality of four-side buttable imager pixels distributed on a wafer substrate (132,133) and an on-chip digitizing electronic readout circuit comprising readout electronics; each of the four-side buttable imager pixels including at least one photodiode configured to be exposed to incident photon radiation; a plurality of pixel groupings formed from among the plurality of imager pixels; the readout electronics including a buffer amplifier for each of the plurality of pixel groupings and the inputs of the buffer amplifier connected to respective outputs of each four-side buttable imager pixel of the pixel grouping; each of the sub-imager pixel arrays further including: a plurality of shared analog front ends (220,222,224,226), the inputs of each shared analog front end connected to respective outputs of multiple buffer amplifiers from among the plurality of pixel groupings; an analog-to-digital converter located at a common centroid location relative to the plurality of shared analog front ends, a sub-imager select I/O line to individually select an output from each of the plurality of shared analog front ends as an input for the analog-to-digital converter; a plurality of shared analog front ends (220,222,224,226), the inputs of each shared analog front end connected to respective outputs of multiple buffer amplifiers from among the plurality of pixel groupings; an analog-to-digital converter located at a common centroid location relative to the plurality of shared analog front ends, a sub-imager select I/O line to individually select an output from each of the plurality of shared analog front ends as an input for the analog-to-digital converter; the analog-to-digital converter having a clock input line, and a shared digital output line that is shared among the respective multiple buffer amplifiers; and wherein a pixel is individually addressable by data provided on the sub-imager select I/O line, and the respective digitized pixel output is provided on the shared digital output line via the respective buffer amplifier.