A computer-implemented method comprising: receiving input data representing an object projected from an object space to a projection space from at least one of a projection image acquisition system, the one or more data storage devices, another one or more data storage devices, a software simulation executed by the one or more processors, or a software simulation executed by another one or more processors; iteratively processing said input data by: computing predicted projection data based on an image representing said object under observation; computing a first quantity for each of a plurality of object space voxels, the first quantity characterizing an output of a monotonic function based on a relationship between value of the input data on a resolution grid and a corresponding value of said predicted projection data on the resolution grid; recording, in the one or more data storage devices, or the another one or more data storage devices, a first data encoding said output of the monotonic function; computing a revised first quantity by weighting said first quantity based on recorded first data from preceding iterations; computing an update value using the revised first quantity; recording, in the one or more data storage devices, or the another one or more data storage devices, a second data set encoding said update values; revising the update values based on the recorded second data set from the preceding iterations; revising said image representing the object under observation using the revised update values, and outputting the reconstructed image to an output device, wherein the output device is at least one of the one or more data storage devices, another one or more data storage devices, a display device, or a printing device. receiving input data representing an object projected from an object space to a projection space from at least one of a projection image acquisition system, the one or more data storage devices, another one or more data storage devices, a software simulation executed by the one or more processors, or a software simulation executed by another one or more processors; iteratively processing said input data by: computing predicted projection data based on an image representing said object under observation; computing a first quantity for each of a plurality of object space voxels, the first quantity characterizing an output of a monotonic function based on a relationship between value of the input data on a resolution grid and a corresponding value of said predicted projection data on the resolution grid; recording, in the one or more data storage devices, or the another one or more data storage devices, a first data encoding said output of the monotonic function; computing a revised first quantity by weighting said first quantity based on recorded first data from preceding iterations; computing an update value using the revised first quantity; recording, in the one or more data storage devices, or the another one or more data storage devices, a second data set encoding said update values; revising the update values based on the recorded second data set from the preceding iterations; revising said image representing the object under observation using the revised update values, and outputting the reconstructed image to an output device, wherein the output device is at least one of the one or more data storage devices, another one or more data storage devices, a display device, or a printing device. computing predicted projection data based on an image representing said object under observation; computing a first quantity for each of a plurality of object space voxels, the first quantity characterizing an output of a monotonic function based on a relationship between value of the input data on a resolution grid and a corresponding value of said predicted projection data on the resolution grid; recording, in the one or more data storage devices, or the another one or more data storage devices, a first data encoding said output of the monotonic function; computing a revised first quantity by weighting said first quantity based on recorded first data from preceding iterations; computing an update value using the revised first quantity; recording, in the one or more data storage devices, or the another one or more data storage devices, a second data set encoding said update values; revising the update values based on the recorded second data set from the preceding iterations; revising said image representing the object under observation using the revised update values, and outputting the reconstructed image to an output device, wherein the output device is at least one of the one or more data storage devices, another one or more data storage devices, a display device, or a printing device.