Re: camera colour spaces
Re: camera colour spaces
- Subject: Re: camera colour spaces
- From: Karsten Krüger <email@hidden>
- Date: Wed, 12 Mar 2008 14:10:07 +0100
While I did not read all postings to this thread...
Some time ago I went thru the whole process of profiling some cameras
(Minolta DiMAGE 7i, A1 und Canon EOS 20D) under several light
conditions.
There were several observations:
- CCD-sensors are, basically speaking, light sensitive transistors
with color
filters for red, blue and green. These filters match exactly one
light condition
to 100%, all other light situations shift sensitivity for each
color filter into
an other direction.
This is the reason why camera CCDs change their gamut under
different light.
Never asume that a choosen profile works for every situation you
are getting
into. And it is in no way a linear process, even when you change
camera settings
according to the light. Sensitivity and gamut change with f-stops,
apperture time
and illumination.
Due to these physical constrains there is no "one size fits all"
solution.
- Video technology based cameras (mostly point & click) have more
information
and time to adjust whitepoint, f-stop and apperture time because
they have all
sensor data available before you actually take a shot.
DSLRs don't have this information. They use sensors like their
analog parents,
do some guessing on what is happening in front of the lens and need
a fast
processor to manage color once the picture is taken.
- Picture data is huge. If a camera does a lot of color management
like Photoshop
it would be too slow for actual use. Color management inside of a
camera has to
be fast and is limited to very simple math. But simple math is the
opposite of
exact color in every situation. So every time a camera takes a JPEG
or TIFF shot,
there is a lot of compromise involved and the output gamut (i.e.
sRGB or AdobeRGB)
is more or less just one out of two image processing modes that
more or less
match one or the other gamut but don't want to be exact at all.
The only one way to get full control on what happens to you image
is to use RAW.
- When you profile a camera in a certain light setting, all light
specific information
gets eliminated. While this is good when you take pictures of
objects for a catalog,
it destroys the mood and feelings of a sunset or a sunny day, which
is not desireable.
So a custom camera profile does not work for every situation.
=> Camera gamuts are shifting, cameras do guesswork, don't have time
to do
great color management and custom profiles don't work for all
purposes.
For a consumer workflow with point & click cameras expectations are
low. As
long as there is a decent output on a local inkjet printer (which
usually tries to match
sRGB) there is no reason to go into details.
If you want a bit more, make a custom profile of your point & click
camera, on a sunny
day, at about 10am and apply it to your pictures. This helps to
eliminate blurry colors
or color shifts and does not eliminate too much of the sunset/sunny
day feelings.
For a professional workflow the only way to gain control is to use RAW
and a RAW
converter on a suitable, calibrated and profiled monitor. And, of
course, understanding
color management.
While many people like Adobe's current products, ACR in my
understanding currently
lacks some essential features:
- There is no way to use custom camera ICC profiles. While this may
not be essential
for many applications, it reduces your flexibility and makes things
complicated when
you need to use your own profiles.
- ACR only allows ProPhoto, sRGB and AdobeRGB as output color spaces.
Modern
L-Star based gamuts like eciRGB v2 provide a better color workspace
for post processing
and professional printing. And there is no way to directly output
into CMYK, which is
an other possibility of loosing image details.
I prefere Capture One Pro because:
- you really can turn of color management to make camera profiles
(Select "Embed camera
profile" and **NO** color conversion is done).
- You can select predefined and your own custom camera ICC profiles as
camera gamut.
- You can output to any RGB or CMYK ICC profile including setting your
rendering intend.
- If you happen to have an ICC profile of your printer (or perhaps use
current offset standard
ISOcoated v2 when you want your pictures print in offset quality),
Capture One reduces
your monitor to the colors of your printer and all your editing
happens in a simulated
CMYK color space - no losses and extremely close to what you are
getting out of your printer.
- You can apply the same settings on a whole set of images on the fly.
- You can output to several workflows at the same time (like sRGB
lowres for web and
ISOcoated v2highres for print)
(the last two items really boost your productivity).
Just my 2 cents on this,
Karsten
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