# Extended PPM (EPPM) Files

EPPM is an extension to the PPM file format that allows specification of metadata. The header of an EPPM file conforms to the following template:

    P6#E
    # Tag1: Value
    # Tag2: Value
    # Tag3: Value
    # .
    # .
    # .
    Width Height Maxval
    Data

Tags recognized by ALE are outlined below.

Black level

The black level tag specifies a value that should be subtracted from all pixels in order to achieve linearity. A modified version of dcraw (darcs repository) can be used to generate files containing this tag.

    # Black-level: <value>

Exposure tags

Exposure tags can be used for determining tonal registration through specification of shutter speed, aperture, and ISO sensitivity (or gain).

    # Shutter: <value>
    # Shutter: 1/<value>
    # Aperture: <f-number>
    # ISO: <value>
    # Gain: <value>