Not sure what you are referring to. I used google translate on you questions.
"Hello, is it possible to remove the black pixelized filter at the bottom of the page?"
Can you provide a screenshot?

Pardon pour le souci de traduction. Sur la photo le fond de la page est blanc en exemple.

Je voudrais enlever le filtre avec tous le point noir, pour avoir un fond de page blanc.

If you are trying to remove the slideshow add this to your custom css for the theme in the admin panel.  admin / themes / customize, and choose the css tab. The empty box is where you put custom css. Be sure to click the save button at the bottom when you are done.
.cb-slideshow, .cb-slideshow::after {
    display: none;
}

To change the background color to white also add this.

body {
    background-color: #fff;
}

Ok Merci beaucoup.