Time Correlated Single Photon Counting (TCSPC) sensors based on Single Photon Avalanche Diodes (SPADs) combined with Time to Digital Converters (TDCs) and histogram-builders have become a prominent tool for depth imaging in recent developments. However, one of the main current limitation of this working mode is intrinsically due to the large amount of data required to generate pixelwise Time of Flight (ToF) histograms. To overcome this limitation in the typical application of intensity/depth map reconstruction, a 2-stage EM algorithm for online peak detection combined with its high-level hardware implementation is proposed. The online estimator solution consists in computing the statistical parameters that directly encode the latent spatial distance and intensity information of the illuminated scene. The evaluation on synthetic data demonstrates its interest with a compression ratio of 0.4% to efficiently reduce the pixel pitch without sacrificing timing resolution.