We describe a new method to developing a realistic fully general relativistic model and computer code of optical projection in a strong, spherically symmetric gravitational field. Classical theoretical analysis of optical projection for an observer in the vicinity of a Schwarzschild black hole was extended to black hole spacetimes with a repulsive cosmological constant (Schwarzschild--de~Sitter spacetimes). In our simulation we consider both null geodesics beyond and ahead of the turning point. Simulation takes care of frequency shift effects, as well as the amplification of intensity. Our code generates static images of sky for static observers and movie simulation for free-falling observers. We use techniques of parallel programming to get high performance and fast run of our code. New interesting investigated effect is diffrent behaviour of apparent angular size of the black hole as a function of the cosmological constant for observers above and under circular photon orbit.