blanking amount and pulse voltage is indicated in the following table 1 table 1______________________________________voltage appliedto blanking port blanking amount______________________________________0 v 0 1 v 10 2 v 30 4 v 75 5 v 100 ______________________________________ meanwhile although the gain is decreased by 6 db according to a preferred embodiment of the present invention the gain decrement of the television luminance signals representing the background screen may be controlled variably for example depending on the voltage of the half blanking trigger signal input to the ym port of color signal processing circuit 50 in an exemplary case the relationship between voltage input to the ym port and gain decrement can be as indicated in table 2 table 2______________________________________ym port voltage gain decrement______________________________________0 v 3 db1 v 6 db3 v 9 db5 v 12 db______________________________________ therefore color signal processing circuit 50 mixes a luminance signal whose gain is adjusted by the half blanking trigger signal with osd characters corresponding to red and or green color information signals combines the mixed signal with a color signal c and then displays osd characters on a screen a screen constructed by the circuit shown in fig2 is shown in fig3 which is explained with reference to fig4 a through 4f in fig3 the period represented by the dashed line a marked on a television screen is indicative of the state where the gain of the television signal is decreased by 6 db in response to a high level half blanking trigger signal by inspection it will be noted that during the period represented by line a only the half blanking trigger signal is high as shown in fig4 e preferably the osd blanking signal and the r and or g signal s representing osd characters are low as shown in fig4 a and 4c in.