How do I apply exposure level info when using dcraw?

I've been using dcraw happily for years for daylight photography
with my Canon 20D, for example, "dcraw -w -c IMG_0001.CR2 aa.raw"
But when I tried making time lapse series of sunsets, I discovered
that my raw images all had the same brightness, more or less,
even as, you know, night came. If I use the -e option to extract
the camera's thumbnails, they have the real (i.e. intuitive)
brightness levels. How to I restore those levels to the full
image output?

Charles Packer
http://cpacker.org
mailboxATcpacker.org

In article ,
wrote:

I've been using dcraw happily for years for daylight photography
with my Canon 20D, for example, "dcraw -w -c IMG_0001.CR2 aa.raw"
But when I tried making time lapse series of sunsets, I discovered
that my raw images all had the same brightness, more or less,
even as, you know, night came. If I use the -e option to extract
the camera's thumbnails, they have the real (i.e. intuitive)
brightness levels. How to I restore those levels to the full
image output?

Charles Packer
http://cpacker.org
mailboxATcpacker.org

Did you use "A" advanced or "P" pro mode on your camera? ;-)
--
teleportation kills

wrote:
I've been using dcraw happily for years for daylight photography
with my Canon 20D, for example, "dcraw -w -c IMG_0001.CR2 aa.raw"
But when I tried making time lapse series of sunsets, I discovered
that my raw images all had the same brightness, more or less,
even as, you know, night came. If I use the -e option to extract
the camera's thumbnails, they have the real (i.e. intuitive)
brightness levels. How to I restore those levels to the full
image output?

From the DCRAW man page:

OUTPUT OPTIONS

By default, dcraw writes PGM/PPM/PAM with 8-bit samples, a
BT.709 gamma curve, a histogram- based white level, and no
metadata.

-W Use a fixed white level, ignoring the image histogram.

-b brightness
Divide the white level by this number, 1.0 by default.

That suggests that "-b 0.5" would increase brightness by 1 stop,
and "-b 2" would decrease brightness by one stop.

So your command, to get a darker image, might look something like this,

dcraw -w -c -W -b 2.3 IMG_0001.CR2 aa.raw

Probably a much more significant point though, is that DCRAW is
great for many things, but generating production quality
photography is not one of them! It is far too difficult to make
even small adjustments by inspection. What it is really great
for is any kind of comparitive work, where the idea is not to
make adjustments but to see exactly how the same processing
affects different images.

For your purposes it would be hugely better to use UFRAW.
Specifically that is because it uses DCRAW to generate the image,
but lets you see immediately how even very slight adjustments
affect an image. It also includes a few other facilities that
DCRAW does not have. It will produce JPEG output, it can set any
specific White Balance that your camera can, and it has visual
graphs for curves. It also provides both a RAW histogram and an
histogram of the resulting RGB image.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)

On Sunday, February 22, 2015 at 12:56:10 PM UTC-5, Floyd L. Davidson wrote:

-W Use a fixed white level, ignoring the image histogram.

-b brightness
Divide the white level by this number, 1.0 by default.



This did it. It was a matter of my non-understanding what "white level"
means. And I'll look into the benefits of ufraw...thanks.

--
Charles Packer
http://cpacker.org
mailboxATcpacker.org