Only using photon mapping to illuminate dielectric or mirror materials is kind of problematic , since their bsdf have dirac distribution. So i use diffuse materials to render image1 which is rendered only by photon mapping(direct and indirect illumination).
Image1(200ssp)compared with image2. photon mapping,radius:0.05,EstimationMaxPhotonNum:10,MaxPhotonNum of photonMap:500000 rendering time:1.4min
Notice the noise pattern of photon mapping. It's different from the random noise pattern of path tracing.
Image2(500ssp) brute-force path tracing(with russian-roulette),rendering time:1.2min
Image3(500ssp)compared with image4. photon mapping,radius:0.05,EstimationMaxPhotonNum:50,MaxPhotonNum of photonMap:500000 rendering time:6.4min. Only use photon mapping to compute the indirect illumination. If you carefully look on the wall, you can still observe the special noise pattern of photon mapping.(some grey areas uniformly distributed.)
Image4(1000ssp) MIS path tracing(with russian-roulette),rendering time:3.5min