Programmatic

<div class="p-py-2">
  <p-button type="button" icon="pi pi-plus" (click)="next()" styleClass="p-button-secondary p-mr-2"></p-button>
  <p-button type="button" icon="pi pi-minus" (click)="prev()" styleClass="p-button-secondary"></p-button>
</div>
<p-galleria
  [(value)]="images"
  [responsiveOptions]="responsiveOptions"
  [containerStyle]="{ 'max-width': '520px' }"
  [numVisible]="5"
  [(activeIndex)]="activeIndex"
>
  <ng-template pTemplate="item" let-item>
    <img [src]="item.previewImageSrc" style="width: 100%" />
  </ng-template>
  <ng-template pTemplate="thumbnail" let-item>
    <div class="p-grid p-nogutter p-justify-center">
      <img [src]="item.thumbnailImageSrc" />
    </div>
  </ng-template>
</p-galleria>