burned zone in RAW file, but not in jpeg

[Paul-Emmanuel GROFFE]

Hi all,

I've been scrolling the mailing list a bit to see if this problem
occured already but couldn't find anything. Please redirect me to the
correct thread if needed.

Now my question: how come that some parts of a photo is burned (no data)
in a raw file, but is ok (not burned, with data) in the jpeg file (shoot
raw+jpeg, canon 450D camera) ? Isn't raw supposed to contain -more-
datas than jpeg  ?

Also, if you have some tips to get data back wihle in RAW I would
appreciate a lot.

Thanks in advance,
regards,
Paul
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[Elle Stone]

OK, this is just a guess. By "burned" do you mean "blown out
highlights"? If so, try negative exposure compensation slider: Click
"Exposure Correction" and move the "Shift (linear) slider to the left.
Also unclick "Auto Brightness". If you've already done all that, then
my apologies, I've misunderstood or there is some other issue
involved.

On 6/10/12, Paul-Emmanuel GROFFE <[hidden email]> wrote:

> Hi all,
>
> I've been scrolling the mailing list a bit to see if this problem
> occured already but couldn't find anything. Please redirect me to the
> correct thread if needed.
>
> Now my question: how come that some parts of a photo is burned (no data)
> in a raw file, but is ok (not burned, with data) in the jpeg file (shoot
> raw+jpeg, canon 450D camera) ? Isn't raw supposed to contain -more-
> datas than jpeg  ?
>
> Also, if you have some tips to get data back wihle in RAW I would
> appreciate a lot.
>
> Thanks in advance,
> regards,
> Paul
> _______________________________________________
> Digikam-users mailing list
> [hidden email]
> https://mail.kde.org/mailman/listinfo/digikam-users
>

--
Elle Stone
http://ninedegreesbelow.com
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[Milan Zamazal]

>>>>> "PG" == Paul-Emmanuel GROFFE <[hidden email]> writes:

    PG> how come that some parts of a photo is burned (no data) in a raw
    PG> file, but is ok (not burned, with data) in the jpeg file (shoot
    PG> raw+jpeg,

I've got the same problem.  I looked into the source code and it seems
that 1% of the brightest and 1% of the darkest areas get cut off when
auto brightness is selected.  This often produces ugly clipped
highlights.  Additionally the raw import tool (for reasons unknown to
me) changes white balance and messes with color spaces (if non-default
color spaces are used).  This makes the raw import tool unusable for me.

But there is a workaround (uncomfortable and slow, but producing good
output): Press cancel after the raw preview is displayed.  Then you
receive the same output as if dcraw from command line was used and
prevents all the above mentioned problems.  You just have to adjust
image brightness yourself.  Also make sure proper defaults are set in
digiKam raw import settings.


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[Milan Zamazal]

>>>>> "MZ" == Milan Zamazal <[hidden email]> writes:

    MZ> Press cancel

I meant Escape key.


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[Remco Viëtor]

On Sunday 10 June 2012 21:52:06 Paul-Emmanuel GROFFE wrote:

> Hi all,

[...]

> Now my question: how come that some parts of a photo is burned (no data)

> in a raw file, but is ok (not burned, with data) in the jpeg file (shoot

> raw+jpeg, canon 450D camera) ? Isn't raw supposed to contain -more-

> datas than jpeg ?

>

 

Hard to say anything without knowing what settings you use in the raw conversion tool in Digikam. My guess is that one or more of those mess up your conversion. So I'll just give a few ideas to check what happens.

 

For settings in the 'Raw Import' tool:

 

in the 'Raw decoding' tab, 'White Balance' section:

- make sure 'method' is set to 'Camera'

- use 'Highlights' -> 'Unclip'

- uncheck all of the check boxes (especially don't use the exposure correction or make sure the sliders are at their default values)

 

Also, make sure that all options in the Post-processing tab are at their default values...

 

These settings should give you a basic conversion, with no brightness scaling, so you'll probably end up with a rather dark image. If you still get blown highlights from the raw file, you have a serious problem :)

 

And yes, theoretically, raw files contain more data than jpeg files (12/14 bits vs. 8). But there are a lot of operations between the raw data and the final image, so lots of occasions to lose information

 

> Also, if you have some tips to get data back wihle in RAW I would 

> appreciate a lot.

 

There I have to disappoint you; no way to get data back that is lost in a previous step. You can prevent losing information though, by being careful in your treatment (using 16 bit/channel helps as well). Also, if one channel is over-exposed/blown in the highlights (usually giving a 'nice' magenta colour), there is an option that /might/ recover detail in those highlights: White Balance -> Highlights -> rebuild (try level 3 first). A faster way to get rid of the magenta colour is White Balance -> Highlights -> Solid white...

 

Remco

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[Milan Zamazal]

Here is an example script I now use for raw conversion.  It's a little
tricky due to the fact that both ImageMagick and netpbm contrast
stretching tools are buggy and can't be used directly on my system.
Please note this is just an example how things can be done and you'll
probably need to set different parameters at least for your camera and
needs.  It's also possible I do something stupid in the script, but it
produces good enough results for me, except for exposure correction
which is better to perform manually than trying to apply naive
approaches.

Actually only very little highlight and darkness clipping is needed,
I'll file a wishlist bug about it.


#!/usr/bin/zsh

set -e

file="$1"
ppmfile="${file%[pP][eE][fF]}ppm"
pngfile="${file%[pP][eE][fF]}png"
xmpfile="$file.xmp"

dcraw -H 5 -w -q 3 -6 "$file"
levels=$(ppmnorm -bpercent 0.01 -wpercent 0.001 -keephues <"$ppmfile" >/dev/null \
         2>>(sed 's/^.*\([0-9][0-9]*\)\.\.\([0-9][0-9]*\) .*$/\1,\2/'))
gamma=1.8
convert "$ppmfile" -level $levels,$gamma -sigmoidal-contrast 3 "$pngfile"
rm "$ppmfile"
exiftool -TagsFromFile "$file" -x Orientation -overwrite_original "$pngfile"
if [ -f "$xmpfile" ]; then
  exiftool -TagsFromFile "$xmpfile" -x Orientation -overwrite_original "$pngfile"
fi

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