Hdmi is not stable on Raspberry Pi3

When installing ubuntu mate on a raspberry pi3, I have a flicking picture on my screen, via HDMI. I suppose my screen cannot display the mode : size or frequency ? I don't know. Does somebody has an idea of the standard mode during installation ?

I have found the right way to boot on HDMI as the config.txt file on the SD card can be modified to force the Raspberry to send a more compatible HDMI mode.
Then it works and I can configure ubuntu Mate