  We predict magnitudes for young planets embedded in transition discs, still
affected by extinction due to material in the disc. We focus on Jupiter-size
planets at a late stage of their formation, when the planet has carved a deep
gap in the gas and dust distributions and the disc starts being transparent to
the planet flux in the infrared (IR). Column densities are estimated by means
of three-dimensional hydrodynamical models, performed for several planet
masses. Expected magnitudes are obtained by using typical extinction properties
of the disc material and evolutionary models of giant planets. For the
simulated cases located at $5.2$ AU in a disc with local unperturbed surface
density of $127$ $\mathrm{g} \cdot \mathrm{cm}^{-2}$, a $1$ $M_J$ planet is
highly extincted in J-, H- and K-bands, with predicted absolute magnitudes $\ge
50$ mag. In L- and M-bands extinction decreases, with planet magnitudes between
$25$ and $35$ mag. In the N-band, due to the silicate feature on the dust
opacities, the expected magnitude increases to $40$ mag. For a $2$ $M_J$
planet, the magnitudes in J-, H- and K-bands are above $22$ mag, while for L-,
M- and N-bands the planet magnitudes are between $15$ and $20$ mag. For the $5$
$M_J$ planet, extinction does not play a role in any IR band, due to its
ability to open deep gaps. Contrast curves are derived for the transition discs
in CQ Tau, PDS70, HL Tau, TW Hya and HD163296. Planet mass upper-limits are
estimated for the known gaps in the last two systems.
