property Zoom: Double;
Enlarge or reduce the size of the thumbnail display.
If a negative value is specified then Zoom will be set to give a thumbnail of that height in pixels (i.e. -22 would set the thumbnail height to 22 pixels).
Note: This property is only recomended for handling of temporary display enlargement. It is better to set the size of the thumbnails
// Show thumbnails at 1/2 size
ImageEnMView1.Zoom := 50;
// Show thumbnails at 24 pixels high
ImageEnMView1.Zoom := -24;