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.
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 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>