With the file extension ALV so-called Adobe Level files of the image editing software Photoshop are marked. Alv files contain adjustment values (histogram values) for the individual channels of the color space RGB (red, green, blue) of an opened image. In the German version they are called tone value correction files.
The dialog box can be reached via the menu item Image-> Adjustments-> Levels, in which also ALV files can be loaded and saved. This makes it easy to apply your own tonal adjustments to an image. Various, often used settings are already included in Photoshop, for example increase contrast, brighten shadows or darken Mitteltne.