Hi Guys,
Don't want to be a bother but what I am observing doesn't make sense to
me... It looks like velvia specifically increases the chance of
artifacts significantly. In particular shooting I had as much as 50%
artifacts in various colors - blue, green, yellow, red. As per the
manual - https://www.darktable.org/usermanual/ch03s04s03.html.php -
velvia saturates more the colors that are already saturated and has less
effect on the colors that are less saturated. It always saturates
however - just the values are less in some areas and more in different.
If we are to take color correction module as a comparison - it always
saturates. So - if I am to turn off velvia and increase saturation with
color correction in theory I should hit the same artifacts (because I am
producing similar colors). In practice - even increasing the saturation
significantly still does not produce artifacts when done with color
corrections module.
In addition - if we are to change the gamut clipping in the input module
to sRGB - it should always confine the colors in this space. I find that
in certain cases even confining the colors to sRGB from the input module
does not help. I turned off the input profile gamut clipping altogether
in an attempt to produce artifacts and I was unable (when velvia is off)
Could there be something wrong with velvia module or my logic is not
right? Or - since my check box is "always use Little CMS 2" should I
consider that this may be the culprit? I have never observed issues
without Little CMS.
Thank you,
B
On 16-06-22 09:27 PM, I. Ivanov wrote:
Hi Rob,
What I am finding is that if the target is SRGB (small) then - bigger
space for clipping as Rec2020 and Adobe RGB do not help. Having the
gamut clipping to SRGB does help. However (and the help does point to
it) color dynamics are affected. In particular - images that do not
exhibit bad clipping loose a lot of tones when forcefully clipped to
SRGB on input color profile. Especially noticeable when there is a
base to compare. To make things more complicated - if I am to tag the
images within darktable module - then export to Adobe RGB would be
affected and printing would suffer. So I literally would have to
isolate these images and use tagging system or color system so the
gamut clipping would be applied on output only (but not when going to
Adobe RGB).
I am curious if there are ways to minimize the effect on first place?
And / or - if I can spot or proof before rendering... The only area
however when I see the clipping is when it is rendered but not in the
darktable module. Is there some best practice that I am missing? My
estimate is about 2%-5% chance to appear (for me).
Regards,
B
On 16-06-21 02:46 PM, I. Ivanov wrote:
Thank you Rob,
I tried Rec2020 RGB - it did not help. Tried export to Adobe RGB - it
"did" help. Then I tried setting the gamut clipping to "SRGB" - this
also "did" help. I can use a temp style on export to avoid clipping.
Regards,
B
On 16-06-14 06:15 PM, Robert William Hutton wrote:
Try this:
In the input color profile module, in the gamut clipping dropdown
list, select linear Rec2020 RGB.
See:
https://www.darktable.org/usermanual/ch03s04s03.html.php#input_color_profile
Regards,
Rob
On 14/06/16 15:42, I. Ivanov wrote:
Hi,
Not sure if this is the proper channel. I am observing the
following color conversion - very odd blues.
This is not the only image but it only happens with the blues.
My setup
- ubuntu 14.04 - 64 bit
- darktable 2.0.4 (I have observed it since 1.6)
other details.
- always use little CSM2 - if I disable this option the colors are
way better in the blues.
- cannot observe on screen before exporting (it is only visible in
the jpg). Actually - if I look
really close I can see the shades but when exported it is extremely
exaggerated.
- another way to remove it or minimize it is by turning off velvia.
The difference in the 2 images is - the bad one - very odd blues
has velvia 40% 0.8 for mid tones.
Thank you...
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