The I²SB framework used to generate Euclid-like VIS predictions from DESI. The image sequence runs between two fixed endpoints, the DESI r-band source x₁ (left) and the Euclid VIS target x₀ (right), through intermediate states x_t. The blue arrow marks the forward bridge interpolation (Equation (1)); the orange arrow marks reverse sampling, in which the U-Net ϵ_θ, conditioned on the DESI z band (c = x_z), predicts an estimate of the Euclid endpoint from x_t, and the posterior update produces the next reverse state. Intermediate frames are model states, not observations.