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Re: qcam-0.91

> I've been playing with the -E flag on the qcam, but I'm not sure what
> format and what values it will take. can anyone out there give me/us a
> brief desc of the -E flag and acceptable values?

From the man page:

     -Eautoexposure-parameters
          Automatically adjust exposure.  -E takes  from  one  to
          five parameters.  They are, in order:

          mode  target-lum  tolerance-lum   std-target-lum   std-
          tolerance-lum
 
          mode is an integer.  Modes 0 and 1 examine the  average
          brightness  of  the  picture, and adjust the brightness
          until the average pixel luminance is in range.  Mode  0
          looks  at  the  whole picture; mode 1 looks at only the
          center ninth of the picture.

          Mode 2 adjusts contrast to get the  standard  deviation
          of the pixel luminance into range.

          Ranges are specified in the next  four  parameters;  if
          they are not supplied, reasonable defaults are used.

          From getopt's point of view, -E  takes  one  parameter.
          So  if  you're  specifying  more  than  one  parameter,
          enclose the parameters in quotes.

A similar description is in the CHANGES file, under the 0.8 delta
comments.  I would love to make the docs clearer, if you can send
me a suggestion on what to put in the man page instead, I'd be
grateful.

You're right that this is not very clear on valid ranges.  Target-lum
has a useful range of 0-15 or 0-63, if you're using 4bpp or 6bpp
respectively.  Tolerance should be a non-negative integer; small
numbers give more consistent pictures, but slow things down.  The
Cam keeps exposing until the average brightness is
(target-lum)+/-(tolerance).  Standard deviation should be a small
non-negative integer; the defaults are 10 (for 6bpp) or 2 (for
4bpp).  Low standard deviation == low contrast.  Tolerance for
standard deviation works the same as exposure tolerance.

Default values for 6bpp are 32, 0, 10, 0.  Default values for 4bpp
are 8, 0, 2, 0.

Brian
References: