RAW pictures: darkness + saturation

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RAW pictures: darkness + saturation

S. Burmeister
Hey everybody!

With dcraw I can set the darkness with the -k option. This is useful if you
e.g get foggy shadows.

Same for saturation: -S.

How can I set these via digikam?

Sven
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Re: RAW pictures: darkness + saturation

Elle Stone
saturation -S is set using
(check) Exposure Correction. Shift linear.

I don't think there is a way to set the -k option using digiKam.

I've experimented and never myself seen any benefit from altering the
"-k", darkness" value that dcraw calculates. It seems that if you
change the calculated "darkness" value, you need to "recolor balance
from the shadow end of the image", so to speak.

So I am really, really curious what camera/type of image you are
processing that benefits from altering the dcraw "-k" value. Do you
have screen shots?

Also, does anyone know what digiKam Highlight EV does?

Kind regards,
Elle

On Tue, 24 Jul 2012 18:09 +0200, Sven Burmeister
<[hidden email]> wrote:

> Hey everybody!
>
> With dcraw I can set the darkness with the -k option. This is useful if you
>
> e.g get foggy shadows.
>
> Same for saturation: -S.
>
> How can I set these via digikam?
>
> Sven
> _______________________________________________
> Digikam-users mailing list
> [hidden email]
> https://mail.kde.org/mailman/listinfo/digikam-users
>


--
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Articles and tutorials on open source digital imaging and photography
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Re: RAW pictures: darkness + saturation

S. Burmeister
Am Dienstag, 24. Juli 2012, 12:50:34 schrieb Elle Stone:
> saturation -S is set using
> (check) Exposure Correction. Shift linear.

If I do not enable that option digikam uses:
Scaling with darkness 0, saturation 4095, and
multipliers 1,707224 1,000000 2,167300 1,000000

If I enable that option and set shift linear to 2.x digikam uses:
Scaling with darkness 0, saturation 4095, and
multipliers 1,707224 1,000000 2,167300 1,000000

If I use dcraw it shows:
dcraw -v -w -S 4000 P1030405.RW2
Loading Panasonic DMC-LX3 image from P1030405.RW2 ...
Scaling with darkness 15, saturation 4000, and
multipliers 1.707224 1.000000 2.167300 1.000000

Are you sure that linear shift is the correct option?

If so this would fit to my other findings about digikam not actually using the
values from the demosaicing tool correctly. Its debug information if started
from a konsole always shows "AHD" even if the amaze algoritm is set. It also
messes up darkness vs. saturation values.

> I don't think there is a way to set the -k option using digiKam.
>
> I've experimented and never myself seen any benefit from altering the
> "-k", darkness" value that dcraw calculates. It seems that if you
> change the calculated "darkness" value, you need to "recolor balance
> from the shadow end of the image", so to speak.
>
> So I am really, really curious what camera/type of image you are
> processing that benefits from altering the dcraw "-k" value. Do you
> have screen shots?

It is one way of getting noise down in dark areas. There might be different
ways to do so but why should one be restricted when it comes to RAW – the
whole point of RAW is that you can set all kinds of things to create the
picture you want.

> Also, does anyone know what digiKam Highlight EV does?

Does not seem to make a difference. :(

Sven
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Re: RAW pictures: darkness + saturation

Elle Stone
On 7/24/12, Sven Burmeister <[hidden email]> wrote:

> Are you sure that linear shift is the correct option?
>
I can't say for certain-sure because I've never looked at the code,
nor monitored digiKam raw processing from the command line. But when
compared to UFRaw, for example, the digiKam linear shift allows you to
pull back the highlights, retaining all the original channel
information, as discussed in this bug report/article:
http://ninedegreesbelow.com/photography/ufraw-highlights.html. Unless
digiKam has changed since I last tested, which was a while ago.

So functionally it acts like "-S". But digiKam uses libraw
(http://www.digikam.org/node/372) rather than dcraw directly. So I
don't think digiKam directly accesses dcraw to do anything. But I
could be wrong.
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Re: RAW pictures: darkness + saturation

S. Burmeister
Am Dienstag, 24. Juli 2012, 15:01:02 schrieb Elle Stone:
> So functionally it acts like "-S". But digiKam uses libraw
> (http://www.digikam.org/node/372) rather than dcraw directly. So I
> don't think digiKam directly accesses dcraw to do anything. But I
> could be wrong.

It's true that digikam uses libraw but they should produce exactly the same
picture if you use libraw with -c 0.

Not sure whether this is compiled and installed by default, but digikam's
source for libkdcraw offers a test folder with dcraw_emu in it. You can run it
as you can dcraw, same options. Yet you have to include the -c 0 because that
is some feature dcraw lacks compared to libraw.

Sven
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