Re: [darktable-user] White balance for old images changed

[Thomas Werzmirzowsky]

Nevermind. I just found the bug that exactly matches my finding:
https://github.com/darktable-org/darktable/issues/7145

On 09.04.21 22:54, werzi2...@gmx.de wrote:


Hello everybody,

for the last couple of days I was checking my image library which also
included having a closer look at some older (2-3 years) images. During
that I noticed that the white balance changed (partly) very
drastically for some of them. It seems that Sony ARW files are most
affected but there are also slight differences in Canon CR2 files. By
closer inspection it seems that the changes are caused by the "White
Balance" module and more specific because of the "camera reference"
instead of the "as shot" setting. For all of the affected images I did
not change this setting. Images that I explicitly set an white balance
for ("from image area" or "user modified") did not change.

I cannot recall what the setting was after the initial import ("camera
reference" or "as shot") but as they looked differently back than (of
that I am sure because I have jpg exports from Darktable) I assume one
of the following happened:

  * The default changed from "as shot" to "camera reference" for old
images
  * The interpretation/implementation of "camera reference" changed

Was there a change like that in the last some years? And is there a
way to revert that? I guess I could change the white balance setting
for the images directly in the library database but I'm not sure how I
can identify those that are affected.

Thanks a lot & Best regards
Thomas



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Re: [darktable-user] White balance Spot Selection & History stack copying

[Jochen Keil]

Hi Bernhard,

sorry for the late reply, I've been on vacation.

I looked briefly at the resources you provided, but I think they don't
solve the problem of flickering white balance / color temperature.

However, in the mean time I cloned darktable's source code repository
and skimmed through the code. I more or less understand how modules
work and I think (?) that the color picker needs mouse focus to work,
which is why it cannot work in the background. I wonder if it's
possible to get the color information for all pixels in the image and
calculate an intermediate color temperature, maybe using a bias value.

If someone can help me on

1) how to get all the necessary color information (e.g. using the
color picker module without GUI interaction(?))
2) the algorithm on how to calculate the color temperature using a bias value

then I think I might be able to write a module for auto white balance.

Btw. Rawtherapee has an AWB mode which works exactly the way described above. :)

Cheers,

  Jochen



On Wed, Aug 1, 2018 at 7:21 PM Bernhard  wrote:
>
> I remembered there was something that reminded me at lrtimelaps - but using 
> darktable - in the past.
> A quick search showed this up:
> https://discuss.pixls.us/t/how-do-you-create-a-time-lapse-on-darktable/8094/14
>  is the newer approach
> https://www.youtube.com/watch?v=C-0bCAIJR0c is the older one.
> Perhaps this might give useful hints (?).
>
> --
>
> regards
> Bernhard
>
> https://www.bilddateien.de
>
>
> Jochen Keil schrieb am 01.08.2018 um 15:05:
>
> Hi,
>
> On Wed, Aug 1, 2018 at 1:31 PM,  wrote:
>
> Jochen Keil (2018-Aug-01, excerpt):
>
> Is there a way to tell darktable that it should analyze each image on its
> own using the selected spot area for white balance?
>
> I doubt it.  I've been asking for the same thing with respect to
> exposure correction (metering a certain region on all images for
> neutral gray).  While “exposure” has an automatic mode (which totally
> did not work for me), there's no such thing in “white balance”.
>
> Implementing this would require darktable to offer two choices when
> copying a setting to another image: Do you want to copy *how* the
> change was determined and apply the result (your use case), or copy
> the change itself (e.g., copy white balance form one photo of a white
> reference to all photos from the same shoot)?  It would be nice to
> have this, but it's probably quite nasty to implement in the
> details...
>
> that's sad to hear. I'd have figured that it might be easy to implement,
> but then I don't know anything about the inner workings of darktable.
>
> Well then, I can only hope that this feature makes it to one of the future
> versions of darktable.
>
> Any suggestions on alternatives or how to fix this?
>
> Thank you,
>
>   Jochen
> 
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>
>
>
>  
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> darktable-user+unsubscr...@lists.darktable.org

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Re: [darktable-user] White balance Spot Selection & History stack copying (& Timelapse)

[J Albrecht]

> On 01 Aug 2018, at 19:21, Bernhard  wrote:
> 
> I remembered there was something that reminded me at lrtimelaps - but using 
> darktable - in the past.
> A quick search showed this up:
> https://discuss.pixls.us/t/how-do-you-create-a-time-lapse-on-darktable/8094/14
>  
> 
>  is


The .jar fie is no longer available at that location. Does anybody know where I 
can find it?



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Re: [darktable-user] White balance Spot Selection & History stack copying

[Bernhard]

I remembered there was something that reminded me at lrtimelaps - but 
using darktable - in the past.

A quick search showed this up:
https://discuss.pixls.us/t/how-do-you-create-a-time-lapse-on-darktable/8094/14 
is the newer approach

https://www.youtube.com/watch?v=C-0bCAIJR0c is the older one.
Perhaps this might give useful hints (?).

--

regards
Bernhard

https://www.bilddateien.de


Jochen Keil schrieb am 01.08.2018 um 15:05:

Hi,

On Wed, Aug 1, 2018 at 1:31 PM,  wrote:

Jochen Keil (2018-Aug-01, excerpt):

Is there a way to tell darktable that it should analyze each image on its
own using the selected spot area for white balance?

I doubt it.  I've been asking for the same thing with respect to
exposure correction (metering a certain region on all images for
neutral gray).  While “exposure” has an automatic mode (which totally
did not work for me), there's no such thing in “white balance”.

Implementing this would require darktable to offer two choices when
copying a setting to another image: Do you want to copy *how* the
change was determined and apply the result (your use case), or copy
the change itself (e.g., copy white balance form one photo of a white
reference to all photos from the same shoot)?  It would be nice to
have this, but it's probably quite nasty to implement in the
details...

that's sad to hear. I'd have figured that it might be easy to implement,
but then I don't know anything about the inner workings of darktable.

Well then, I can only hope that this feature makes it to one of the future
versions of darktable.

Any suggestions on alternatives or how to fix this?

Thank you,

   Jochen

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Re: [darktable-user] White balance Spot Selection & History stack copying

[Lorenzo Bolzani]

I'd like this too for lens correction: the lens may be always the same but
at different focal lengths.

Now I have to enable it one by one for each photo.

2018-08-01 13:31 GMT+02:00 :

> Jochen Keil (2018-Aug-01, excerpt):
> > Is there a way to tell darktable that it should analyze each image on its
> > own using the selected spot area for white balance?
>
> I doubt it.  I've been asking for the same thing with respect to
> exposure correction (metering a certain region on all images for
> neutral gray).  While “exposure” has an automatic mode (which totally
> did not work for me), there's no such thing in “white balance”.
>
> Implementing this would require darktable to offer two choices when
> copying a setting to another image: Do you want to copy *how* the
> change was determined and apply the result (your use case), or copy
> the change itself (e.g., copy white balance form one photo of a white
> reference to all photos from the same shoot)?  It would be nice to
> have this, but it's probably quite nasty to implement in the
> details...
>
>
> 
> [1] https://www.mail-archive.com/darktable-user@lists.
> darktable.org/msg00371.html
>
>
> --
> http://stefan-klinger.deo/X
> I prefer receiving plain text messages, not exceeding 32kB. /\/
>   \
> 
> 
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> lists.darktable.org
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>


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Re: [darktable-user] White balance Spot Selection & History stack copying

[dt-list]

Jochen Keil (2018-Aug-01, excerpt):
> Is there a way to tell darktable that it should analyze each image on its
> own using the selected spot area for white balance?

I doubt it.  I've been asking for the same thing with respect to
exposure correction (metering a certain region on all images for
neutral gray).  While “exposure” has an automatic mode (which totally
did not work for me), there's no such thing in “white balance”.

Implementing this would require darktable to offer two choices when
copying a setting to another image: Do you want to copy *how* the
change was determined and apply the result (your use case), or copy
the change itself (e.g., copy white balance form one photo of a white
reference to all photos from the same shoot)?  It would be nice to
have this, but it's probably quite nasty to implement in the
details...



[1] 
https://www.mail-archive.com/darktable-user@lists.darktable.org/msg00371.html


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Re: [darktable-user] white balance

[Tim Rolph]

Hello, the card I use is two sided, it has white grey and black on one side 
and the standard 24 colors on the other and yes you can use Adobe DNG to 
produce a color profile for use in Lightroom and rawtherapee. However I use it 
mostly for a custom WB in camera on my 14 year old DSLR canon it is just a 
matter of taking one full frame image of the WB side of the card and then 
telling the camera to use the custom WB image. Of course you need to change 
images if the lighting changes significantly and you can also use it within dt 
with the spot wb option.
While on the subject of colour profiles I have recently used the excellent 
darktable-chart programme to create a profile and tone curve using a wolf faust 
it8 scanner calibration target that I purchased for 15.00 euros back in 2009 
and I can say it is better that any other profile that I have produced using 
any other method.

Tim.
 
On Saturday, 25 February 2017 16:10:36 GMT Remco Viëtor wrote:
> On samedi 25 février 2017 01:38:01 CET Marcus Sundman wrote:
> > Well, first we need sensible support for color cards in darktable. (Now
> > you have to go through crazy many hoops to set your whitebalance from a
> > color card, including multiple import/export and profile generation in
> > an external program and custom command line tools and whatnot.)
> 
> First you need a correctly calibrated and profiled screen (and printer if
> you plan on printing). Without that, you'd have to work strictly by the
> numbers, because there's no way you can visualise the final result. (OK, if
> you publish on the web, >90% of the viewers won't have a profiled screen,
> but at least you know how it should look)
> 
> Then, setting your white balance from a *colour* card is looking for trouble
> (if it is at all possible to get any decent white balance from such a
> card).
> 
> As has been said already, for a white balance, you need a neutral spot in
> your image: light or dark gray, but not white or black. (Such a spot can of
> course be a *neutral* spot on your colour card). Remember that 'setting the
> white balance' means changing the ratios green/red and green/blue (in
> practice, green is set to 1.0, and the red and blue channels are multiplied
> by one value each, depending on colour temperature and tint, DT _shows_
> those multipliers in the white balance module, and allows you to change
> them directly).
> 
> When you have that neutral spot in your image, in DT it's just a matter of
> choosing the "spot" mode in the white balance module and select a rectangle
> on the neutral spot.
> 
> The colour patches are used to create a *camera profile*, and yes, this
> needs an external programme (or two), just like screen or printer
> profiling. *Unlike* screen and printer profiling, it's something that's
> mostly needed for very colour critical work. (the few times I bothered with
> a camera profile, the results with a custom profile were identical or
> nearly identical to the default profile and I had no way to show which was
> better) And when you get to that level, you also have to be very careful
> about your lights all having the same colour, as the colour of the incoming
> lights influences what the camera "sees".
> 
> And just a small question: is there *any* raw developer that includes the
> possibility to generate an input profile from a colour card?
> 
> Remco
> 
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Re: [darktable-user] white balance

[Remco Viëtor]

On samedi 25 février 2017 01:38:01 CET Marcus Sundman wrote:

> Well, first we need sensible support for color cards in darktable. (Now
> you have to go through crazy many hoops to set your whitebalance from a
> color card, including multiple import/export and profile generation in
> an external program and custom command line tools and whatnot.)

First you need a correctly calibrated and profiled screen (and printer if you 
plan on printing). Without that, you'd have to work strictly by the numbers, 
because there's no way you can visualise the final result. (OK, if you publish 
on the web, >90% of the viewers won't have a profiled screen, but at least you 
know how it should look)

Then, setting your white balance from a *colour* card is looking for trouble 
(if it is at all possible to get any decent white balance from such a card).

As has been said already, for a white balance, you need a neutral spot in your 
image: light or dark gray, but not white or black. (Such a spot can of course 
be a *neutral* spot on your colour card). Remember that 'setting the white 
balance' means changing the ratios green/red and green/blue (in practice, 
green is set to 1.0, and the red and blue channels are multiplied by one value 
each, depending on colour temperature and tint, DT _shows_ those multipliers 
in the white balance module, and allows you to change them directly).

When you have that neutral spot in your image, in DT it's just a matter of 
choosing the "spot" mode in the white balance module and select a rectangle on 
the neutral spot.

The colour patches are used to create a *camera profile*, and yes, this needs 
an external programme (or two), just like screen or printer profiling. 
*Unlike* screen and printer profiling, it's something that's mostly needed for 
very colour critical work. (the few times I bothered with a camera profile, 
the results with a custom profile were identical or nearly identical to the 
default profile and I had no way to show which was better) And when you get to 
that level, you also have to be very careful about your lights all having the 
same colour, as the colour of the incoming lights influences what the camera 
"sees".

And just a small question: is there *any* raw developer that includes the 
possibility to generate an input profile from a colour card? 

Remco

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Re: [darktable-user] white balance

[Steven Fosdick]

Note that if you take a picture of a white card and fill the frame with it
in an auto-exposure mode it will come out grey anyway.

What I am not sure has been completely addresses is how all of this would
work together.  I assume you would not have a card in each shot but would
start a shoot with the card and the proceed to take photos of the subject
you really want.  When you get the pictures into DT you'd want to set the
white balance from the card in the first pic and then apply it to the rest
of the pictures.

Let's assume you opened the first picture, select spot white balance,
select a decent region in the middle of the card, then returned to light
table mode and copy the white balance setting from that first picture to
the rest.  What I am not sure about is whether it would copy the white
balance numbers, i.e. the adjustment to R, G and B or whether it would copy
the intent, i.e. copy parameters to the white balance module that say
select rectangle x,y,w,h and use that to do spot white balance.  If the
latter it would not give the desired effect.

On 23 February 2017 at 18:23, Tim Rolph  wrote:

> On Tuesday, 21 February 2017 16:16:30 GMT Michael wrote:
> > is there something where we can take a picture of a gray card and then we
> > click on it and then dt will adjust all of the colors so that the gray
> card
> > is
> > 33-33-33%?
> >
> > by the way: what is the color of the remaining 1%
> Anyone wanting a grey / white balance / 24 patch color card should checkout
> the following.
>
> www.greywhitebalancecolourcard.co.uk
>
> I have one of these and am very pleased with it and it's a fraction of the
> cost of the Mcbeth cards.
>
> 
> 
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>
>


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Re: [darktable-user] white balance

[Tim Rolph]

On Tuesday, 21 February 2017 16:16:30 GMT Michael wrote:
> is there something where we can take a picture of a gray card and then we
> click on it and then dt will adjust all of the colors so that the gray card
> is
> 33-33-33%?
> 
> by the way: what is the color of the remaining 1%
Anyone wanting a grey / white balance / 24 patch color card should checkout 
the following.

www.greywhitebalancecolourcard.co.uk

I have one of these and am very pleased with it and it's a fraction of the 
cost of the Mcbeth cards.


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Re: [darktable-user] white balance

[Michael]

So with raw and dt it is okay to zoom in on the spot? What I mean  is when
you take the picture  do you take one (with the white spot in it) or two
(one with and one without). I'm thinking two but just to be sure.

You know. I actually like this idea. I'm going to tape a couple of
pieces of white printer paper together and then tape that to a folder and
use that to white balance off of.

On Wed, Feb 22, 2017 at 5:14 PM, Michael  wrote:

> so with raw and dt it is okay to zoom in on the spot? What I mean  is when
> you take the picture  do you take one (with the white spot in it) or twon
> (one with and one without). I'm thinking two but just to be sure.
>
> On Wed, Feb 22, 2017 at 4:07 PM, Martin Burri  wrote:
>
>> If you shoot in raw then it only needs to give a big enough patch to use
>> the dt white balance tool on it.
>>
>> If tuning the in-camera white-balance setting, then i think you must
>> refer to the camera manual, since there is probably no universal answer.
>>
>> Best regards,
>> Martin
>> Am 22.02.2017 21:50 schrieb Michael :
>>
>> sounds good but shouldn't it be bigger? Or else how close can you
>> be when taking the white balance picture? An exposure picture off of a gray
>> card? So it does NOT need to cover most of the field of view?
>>
>> On Wed, Feb 22, 2017 at 3:27 PM, Martin Burri  wrote:
>>
>> There is a way more reliable DIY way than printing:
>> https://photographylife.com/diy-reliable-and-cheap-universal
>> -white-balance-reference-device
>>
>> I tried it and compared the result with a real gray card. I was unable to
>> see a difference between both methods. So, teflon comes close enough at
>> least for my visual perception :-)
>>
>> Best regards,
>> Martin
>>
>> On 22.02.2017 05:21, Michael wrote:
>>
>> Well, I guess I can try to print a gray card!
>> Anyone know what the code is for 18% gray? If 18% is right in the middle
>> of the shades of gray I found one page (http://www.computerhope.com/c
>> gi-bin/htmlcolor.pl?c=808080) that says the code is:
>> 808080
>> and according to the same page it is made up of equal part RGB
>> *W3C Color Name:* Grey
>> *RGB:* 128, 128, 128
>> *HSL:* 0.00, 0.00, 0.50
>> so what is the authoritative answer?
>>
>> On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman  wrote:
>>
>> On 21/02/17 23:16, Michael wrote:
>>
>> is there something where we can take a picture of a gray card and then we
>> click on it and then dt will adjust all of the colors so that the gray card
>> is
>> 33-33-33%?
>>
>> Usually you use "18% gray" meaning a card that reflects 18% of the light
>> in the visible spectrum and equal amounts of red, green and blue.
>>
>> It might actually be nice if the whitebalance module would support
>> exposure adjustment as well, to make a selected area a specific brightness,
>> or what do others think?
>>
>> by the way: what is the color of the remaining 1%
>>
>> That "33-33-33%" is your invention, so nobody but you can know what
>> "remaining 1%" you are talking about. If you were talking about the
>> reflected % of the individual color channels then there is no "remaining
>> 1%", but the "remaining" (absorbed) amounts of light are 67%, 67% and 67%,
>> respectively.
>>
>>
>> - Marcus
>>
>>
>>
>>
>> --
>> :-)~MIKE~(-:
>>
>> 
>> darktable user mailing list to unsubscribe send a mail to
>> darktable-user+unsubscr...@lists.darktable.org
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>>
>>
>> 
>> darktable user mailing list to unsubscribe send a mail to
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>>
>>
>>
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>>
>>
>
>
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>



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Re: [darktable-user] white balance

[Martin Burri]

There is a way more reliable DIY way than printing:
https://photographylife.com/diy-reliable-and-cheap-universal-white-balance-reference-device

I tried it and compared the result with a real gray card. I was unable 
to see a difference between both methods. So, teflon comes close enough 
at least for my visual perception :-)


Best regards,
Martin

On 22.02.2017 05:21, Michael wrote:

Well, I guess I can try to print a gray card!
Anyone know what the code is for 18% gray? If 18% is right in the 
middle of the shades of gray I found one page 
(http://www.computerhope.com/cgi-bin/htmlcolor.pl?c=808080) that says 
the code is:

808080
and according to the same page it is made up of equal part RGB
*W3C Color Name:* Grey
*RGB:* 128, 128, 128
*HSL:* 0.00, 0.00, 0.50
so what is the authoritative answer?

On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman > wrote:


On 21/02/17 23:16, Michael wrote:

is there something where we can take a picture of a gray card
and then we click on it and then dt will adjust all of the
colors so that the gray card is
33-33-33%?

Usually you use "18% gray" meaning a card that reflects 18% of the
light in the visible spectrum and equal amounts of red, green and
blue.

It might actually be nice if the whitebalance module would support
exposure adjustment as well, to make a selected area a specific
brightness, or what do others think?

by the way: what is the color of the remaining 1%

That "33-33-33%" is your invention, so nobody but you can know
what "remaining 1%" you are talking about. If you were talking
about the reflected % of the individual color channels then there
is no "remaining 1%", but the "remaining" (absorbed) amounts of
light are 67%, 67% and 67%, respectively.


- Marcus




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Re: [darktable-user] white balance

[Michael]

The reason I didn't get it is that it was sent to spam sorry about the
clutter

On Wed, Feb 22, 2017 at 3:23 PM, Michael  wrote:

> I always thought white balance should be done off of a white card not that
> I understand how (why might be a better term) selecting an area of a color
> (or even multiple colors) adjusts all colors or how it does it. I would
> think if you should select a 18% gray/ x brightness white card area the
> computer should adjust that area to be that gray/white and adjust the RGB
> colors around it to match. That is what I meant originally.
>
> In any case. how do you use the gray card to set exposure.
> (also please cc the list because the only reason I got this message
>  from Lorenzo is because it was in someones inline)
>
>
>> 2017-02-22 8:36 GMT+01:00 Lorenzo Bolzani :
>>>
 Printing a gray card is a bad idea: you need a very good an perfectly
 calibrated printer for this and good non-glossy paper. Otherwise you do not
 get perfect gray and you get a random shade of color in all your shots
 where you use it. Just buy one.

 For white balance, as Ivanov said, any gray is good, actually you
 typically use a white card. So *just take a white sheet from the
 printer a use that.* I did this in several occasions and works really
 fine. The minor problem is that paper is not "perfectly neutral white" but
 can vary slightly so if you are looking for ultimate perfection buy a WB
 card (X-Rite, Opteka, etc.).

 The gray 18% thing is about setting the exposure, not the white
 balance. Of course you can use the gray card for white balance too but it's
 not its main purpose. Typically gray 18 targets are white on the other side
 for WB.

 Often white balance cards came in set of three pieces: white, gray and
 black. Almost always the gray here is not gray 18 so it is not good for
 exposure reference only for WB.


 Bye

 Lorenzo


 2017-02-22 5:57 GMT+01:00 I. Ivanov :

> For the purpose of white balance - I don't think it really matters if
> it is 18% or less or more. It is just pure gray. As long as you use a card
> and then use it to measure white balance you should be fine.
>
> On 2017-02-21 08:21 PM, Michael wrote:
>
> Well, I guess I can try to print a gray card!
> Anyone know what the code is for 18% gray? If 18% is right in the
> middle of the shades of gray I found one page (
> http://www.computerhope.com/cgi-bin/htmlcolor.pl?c=808080) that says
> the code is:
> 808080
> and according to the same page it is made up of equal part RGB
> *W3C Color Name:* Grey
> *RGB:* 128, 128, 128
> *HSL:* 0.00, 0.00, 0.50
> so what is the authoritative answer?
>
> On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman 
> wrote:
>
>> On 21/02/17 23:16, Michael wrote:
>>
>> is there something where we can take a picture of a gray card and
>>> then we click on it and then dt will adjust all of the colors so that 
>>> the
>>> gray card is
>>> 33-33-33%?
>>>
>> Usually you use "18% gray" meaning a card that reflects 18% of the
>> light in the visible spectrum and equal amounts of red, green and blue.
>>
>> It might actually be nice if the whitebalance module would support
>> exposure adjustment as well, to make a selected area a specific 
>> brightness,
>> or what do others think?
>>
>> by the way: what is the color of the remaining 1%
>>>
>> That "33-33-33%" is your invention, so nobody but you can know what
>> "remaining 1%" you are talking about. If you were talking about the
>> reflected % of the individual color channels then there is no "remaining
>> 1%", but the "remaining" (absorbed) amounts of light are 67%, 67% and 
>> 67%,
>> respectively.
>>
>>
>> - Marcus
>>
>>
>
>
> --
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Re: [darktable-user] white balance

[Michael]

I always thought white balance should be done off of a white card not that
I understand how (why might be a better term) selecting an area of a color
(or even multiple colors) adjusts all colors or how it does it. I would
think if you should select a 18% gray/ x brightness white card area the
computer should adjust that area to be that gray/white and adjust the RGB
colors around it to match. That is what I meant originally.

In any case. how do you use the gray card to set exposure.
(also please cc the list because the only reason I got this message
 from Lorenzo is because it was in someones inline)


> 2017-02-22 8:36 GMT+01:00 Lorenzo Bolzani :
>>
>>> Printing a gray card is a bad idea: you need a very good an perfectly
>>> calibrated printer for this and good non-glossy paper. Otherwise you do not
>>> get perfect gray and you get a random shade of color in all your shots
>>> where you use it. Just buy one.
>>>
>>> For white balance, as Ivanov said, any gray is good, actually you
>>> typically use a white card. So *just take a white sheet from the
>>> printer a use that.* I did this in several occasions and works really
>>> fine. The minor problem is that paper is not "perfectly neutral white" but
>>> can vary slightly so if you are looking for ultimate perfection buy a WB
>>> card (X-Rite, Opteka, etc.).
>>>
>>> The gray 18% thing is about setting the exposure, not the white balance.
>>> Of course you can use the gray card for white balance too but it's not its
>>> main purpose. Typically gray 18 targets are white on the other side for WB.
>>>
>>> Often white balance cards came in set of three pieces: white, gray and
>>> black. Almost always the gray here is not gray 18 so it is not good for
>>> exposure reference only for WB.
>>>
>>>
>>> Bye
>>>
>>> Lorenzo
>>>
>>>
>>> 2017-02-22 5:57 GMT+01:00 I. Ivanov :
>>>
 For the purpose of white balance - I don't think it really matters if
 it is 18% or less or more. It is just pure gray. As long as you use a card
 and then use it to measure white balance you should be fine.

 On 2017-02-21 08:21 PM, Michael wrote:

 Well, I guess I can try to print a gray card!
 Anyone know what the code is for 18% gray? If 18% is right in the
 middle of the shades of gray I found one page (
 http://www.computerhope.com/cgi-bin/htmlcolor.pl?c=808080) that says
 the code is:
 808080
 and according to the same page it is made up of equal part RGB
 *W3C Color Name:* Grey
 *RGB:* 128, 128, 128
 *HSL:* 0.00, 0.00, 0.50
 so what is the authoritative answer?

 On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman  wrote:

> On 21/02/17 23:16, Michael wrote:
>
> is there something where we can take a picture of a gray card and then
>> we click on it and then dt will adjust all of the colors so that the gray
>> card is
>> 33-33-33%?
>>
> Usually you use "18% gray" meaning a card that reflects 18% of the
> light in the visible spectrum and equal amounts of red, green and blue.
>
> It might actually be nice if the whitebalance module would support
> exposure adjustment as well, to make a selected area a specific 
> brightness,
> or what do others think?
>
> by the way: what is the color of the remaining 1%
>>
> That "33-33-33%" is your invention, so nobody but you can know what
> "remaining 1%" you are talking about. If you were talking about the
> reflected % of the individual color channels then there is no "remaining
> 1%", but the "remaining" (absorbed) amounts of light are 67%, 67% and 67%,
> respectively.
>
>
> - Marcus
>
>


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Re: [darktable-user] white balance

[Lorenzo Bolzani]

Hi Jean-Luc,
how would you proceed in detail with this module? Would you start with the
lift, gain or gamma or a little from all three? How many patches would you
pick?

I have a few pictures with heavy color casts (from slide scanning) and
while I can get good results the effort is often very high and I have yet
to find a reliable way to simplify the process.

Here is an example:

https://www.flickr.com/photos/133025950@N04/32240744713/in/dateposted-public/

https://www.flickr.com/photos/133025950@N04/32929837971/in/dateposted-public/


I just tried to use the color balance module on this shot, as I did several
other times, but I never got great results. The same for Lab curves. The
best result I've got, the one above, was using "color mapping" but I
consider it pure luck.

In this picture there is nothing clearly neutral so it is quite hard to use
about anything.


Thanks for any suggestion



Bye

Lorenzo

2017-02-22 10:39 GMT+01:00 Jean-Luc Coulon (f5ibh) <
jean.luc.cou...@gmail.com>:

> Hi,
>
> I think this post is going outside the original question.
>
> The original question was about a grey card and white balance (I I
> understood corrrectly).
> And what to do if the grey card doesnt appear "neutral" in darktable.
>
> 1 - Grey card and white balance.
> The fact that the card is 18%, 22% or anything else is unrelevant if we
> speak of white balance (the 18% is useful for exposure control... well, I
> will no enter the debate about calibration and the various mid-grey,
> median-grey or so)
> So, yes, we can set the white balance using the "spot" white balance on a
> grey card as soon as the grey is neutral.
> Neutral means "the same value for red, green, blue".
>
> 2 - Card is not neutral
> If the grey is not neutral, say a colour cast with one of the channel with
> a different value, your white balance will give a colour cast in the
> opposite direction.
> You can correct that in dt with the module "colour balance" for instance
> by selecting the neutral area of interest with the colour picker and trying
> to have the same value for all the 3 channels.
> But, in my opinion, if your grey card is reasonably neutral, you well not
> see (with your eyes) any difference.
> A simple sheet of (white) paper can also do the job.
>
> About the reflectivity of the neutral grey : it is an other matter. Such
> grey card can be used to adjust the exposure. But as there are strong
> controversies about what should be the neutrality of a neutral grey, this
> subject is prone to leave to various trolls.
>
> Regards
>
> Jean-Luc
>
> 2017-02-22 8:36 GMT+01:00 Lorenzo Bolzani :
>
>> Printing a gray card is a bad idea: you need a very good an perfectly
>> calibrated printer for this and good non-glossy paper. Otherwise you do not
>> get perfect gray and you get a random shade of color in all your shots
>> where you use it. Just buy one.
>>
>> For white balance, as Ivanov said, any gray is good, actually you
>> typically use a white card. So *just take a white sheet from the printer
>> a use that.* I did this in several occasions and works really fine. The
>> minor problem is that paper is not "perfectly neutral white" but can vary
>> slightly so if you are looking for ultimate perfection buy a WB card
>> (X-Rite, Opteka, etc.).
>>
>> The gray 18% thing is about setting the exposure, not the white balance.
>> Of course you can use the gray card for white balance too but it's not its
>> main purpose. Typically gray 18 targets are white on the other side for WB.
>>
>> Often white balance cards came in set of three pieces: white, gray and
>> black. Almost always the gray here is not gray 18 so it is not good for
>> exposure reference only for WB.
>>
>>
>> Bye
>>
>> Lorenzo
>>
>>
>> 2017-02-22 5:57 GMT+01:00 I. Ivanov :
>>
>>> For the purpose of white balance - I don't think it really matters if it
>>> is 18% or less or more. It is just pure gray. As long as you use a card and
>>> then use it to measure white balance you should be fine.
>>>
>>> On 2017-02-21 08:21 PM, Michael wrote:
>>>
>>> Well, I guess I can try to print a gray card!
>>> Anyone know what the code is for 18% gray? If 18% is right in the middle
>>> of the shades of gray I found one page (http://www.computerhope.com/c
>>> gi-bin/htmlcolor.pl?c=808080) that says the code is:
>>> 808080
>>> and according to the same page it is made up of equal part RGB
>>> *W3C Color Name:* Grey
>>> *RGB:* 128, 128, 128
>>> *HSL:* 0.00, 0.00, 0.50
>>> so what is the authoritative answer?
>>>
>>> On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman  wrote:
>>>
 On 21/02/17 23:16, Michael wrote:

 is there something where we can take a picture of a gray card and then
> we click on it and then dt will adjust all of the colors so that the gray
> card is
> 33-33-33%?
>
 Usually you use "18% gray" meaning a card that reflects 18% of the
 light in the visible spectrum and equal amounts of red, green 

Re: [darktable-user] white balance

[Jean-Luc Coulon (f5ibh)]

Hi,

I think this post is going outside the original question.

The original question was about a grey card and white balance (I I
understood corrrectly).
And what to do if the grey card doesnt appear "neutral" in darktable.

1 - Grey card and white balance.
The fact that the card is 18%, 22% or anything else is unrelevant if we
speak of white balance (the 18% is useful for exposure control... well, I
will no enter the debate about calibration and the various mid-grey,
median-grey or so)
So, yes, we can set the white balance using the "spot" white balance on a
grey card as soon as the grey is neutral.
Neutral means "the same value for red, green, blue".

2 - Card is not neutral
If the grey is not neutral, say a colour cast with one of the channel with
a different value, your white balance will give a colour cast in the
opposite direction.
You can correct that in dt with the module "colour balance" for instance by
selecting the neutral area of interest with the colour picker and trying to
have the same value for all the 3 channels.
But, in my opinion, if your grey card is reasonably neutral, you well not
see (with your eyes) any difference.
A simple sheet of (white) paper can also do the job.

About the reflectivity of the neutral grey : it is an other matter. Such
grey card can be used to adjust the exposure. But as there are strong
controversies about what should be the neutrality of a neutral grey, this
subject is prone to leave to various trolls.

Regards

Jean-Luc

2017-02-22 8:36 GMT+01:00 Lorenzo Bolzani :

> Printing a gray card is a bad idea: you need a very good an perfectly
> calibrated printer for this and good non-glossy paper. Otherwise you do not
> get perfect gray and you get a random shade of color in all your shots
> where you use it. Just buy one.
>
> For white balance, as Ivanov said, any gray is good, actually you
> typically use a white card. So *just take a white sheet from the printer
> a use that.* I did this in several occasions and works really fine. The
> minor problem is that paper is not "perfectly neutral white" but can vary
> slightly so if you are looking for ultimate perfection buy a WB card
> (X-Rite, Opteka, etc.).
>
> The gray 18% thing is about setting the exposure, not the white balance.
> Of course you can use the gray card for white balance too but it's not its
> main purpose. Typically gray 18 targets are white on the other side for WB.
>
> Often white balance cards came in set of three pieces: white, gray and
> black. Almost always the gray here is not gray 18 so it is not good for
> exposure reference only for WB.
>
>
> Bye
>
> Lorenzo
>
>
> 2017-02-22 5:57 GMT+01:00 I. Ivanov :
>
>> For the purpose of white balance - I don't think it really matters if it
>> is 18% or less or more. It is just pure gray. As long as you use a card and
>> then use it to measure white balance you should be fine.
>>
>> On 2017-02-21 08:21 PM, Michael wrote:
>>
>> Well, I guess I can try to print a gray card!
>> Anyone know what the code is for 18% gray? If 18% is right in the middle
>> of the shades of gray I found one page (http://www.computerhope.com/c
>> gi-bin/htmlcolor.pl?c=808080) that says the code is:
>> 808080
>> and according to the same page it is made up of equal part RGB
>> *W3C Color Name:* Grey
>> *RGB:* 128, 128, 128
>> *HSL:* 0.00, 0.00, 0.50
>> so what is the authoritative answer?
>>
>> On Tue, Feb 21, 2017 at 7:53 PM, Marcus Sundman  wrote:
>>
>>> On 21/02/17 23:16, Michael wrote:
>>>
>>> is there something where we can take a picture of a gray card and then
 we click on it and then dt will adjust all of the colors so that the gray
 card is
 33-33-33%?

>>> Usually you use "18% gray" meaning a card that reflects 18% of the light
>>> in the visible spectrum and equal amounts of red, green and blue.
>>>
>>> It might actually be nice if the whitebalance module would support
>>> exposure adjustment as well, to make a selected area a specific brightness,
>>> or what do others think?
>>>
>>> by the way: what is the color of the remaining 1%

>>> That "33-33-33%" is your invention, so nobody but you can know what
>>> "remaining 1%" you are talking about. If you were talking about the
>>> reflected % of the individual color channels then there is no "remaining
>>> 1%", but the "remaining" (absorbed) amounts of light are 67%, 67% and 67%,
>>> respectively.
>>>
>>>
>>> - Marcus
>>>
>>>
>>
>>
>> --
>> :-)~MIKE~(-:
>>
>> 
>> darktable user mailing list to unsubscribe send a mail to
>> darktable-user+unsubscr...@lists.darktable.org
>>
>>
>>
>> 
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>> darktable-user+unsubscr...@lists.darktable.org
>>
>
>
> 
> darktable user 

Re: [darktable-user] white balance

[Marcus Sundman]

On 21/02/17 23:16, Michael wrote:

is there something where we can take a picture of a gray card and then 
we click on it and then dt will adjust all of the colors so that the 
gray card is

33-33-33%?
Usually you use "18% gray" meaning a card that reflects 18% of the light 
in the visible spectrum and equal amounts of red, green and blue.


It might actually be nice if the whitebalance module would support 
exposure adjustment as well, to make a selected area a specific 
brightness, or what do others think?



by the way: what is the color of the remaining 1%
That "33-33-33%" is your invention, so nobody but you can know what 
"remaining 1%" you are talking about. If you were talking about the 
reflected % of the individual color channels then there is no "remaining 
1%", but the "remaining" (absorbed) amounts of light are 67%, 67% and 
67%, respectively.



- Marcus


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Re: [darktable-user] white balance

[I. Ivanov]

Not sure I understand but if you take a picture of a gray card - you can 
use the white balance module and in the drop down select custom and then 
select from the gray patch that you have taken picture from.


https://www.darktable.org/usermanual/ch03s04.html.php

3.4.1.10. White balance

the drop down of the preset.

Regards,

B



On 2017-02-21 01:16 PM, Michael wrote:
is there something where we can take a picture of a gray card and then 
we click on it and then dt will adjust all of the colors so that the 
gray card is

33-33-33%?

by the way: what is the color of the remaining 1%
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Re: [darktable-user] White balance on a TrueColor scuadra, using provided Lab values

[KOVÁCS István]

One more thing regarding the colour picker: it works in your display's
colour space, which may affect its Lab readings - the devs would know.
https://www.darktable.org/usermanual/ch03s03s04.html.php


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Re: [darktable-user] White balance on a TrueColor scuadra, using provided Lab values

[KOVÁCS István]

My bad, sorry, I thought the card had colour patches, too - I've only ever
used a simple Whibal card, and does not provide Lab values. Also, I don't
understand why you mentioned exposure in your post, I thought you expected
darktable to adjust it automatically when you picked white balance from the
card. Sorry about that.

Kofa


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Re: [darktable-user] White balance on a TrueColor scuadra, using provided Lab values

[Emmanuel Lacour]

Le 05/09/2016 à 13:47, KOVÁCS István a écrit :
> Hi,
> 
> If I get this correctly, the card has grey patches as well as colour ones.

no, only grey (and blck/white, but I don't really use them):

http://www.scuadra.fr/en/charte.php?Language=en


it's mostly for WB

> The spot white balance tool adjusts white balance only, meaning that:
> - after adjustments, grey should be grey (neutral)


but it's practically impossible to produce materials with exact neutral
grey as standardized in photo. Hence, each grey card gives accurate Lab
values measured by spectrophotometer, so I tried to find a quick way to
adjust the WB based on those values.

> - exposure is to be done independently

of course.

> - colour in non-grey patches, as well as the lightness of all patches
> are influenced by the camera profile. See darktable's documentation on
> that topic.
> 

right, but it seems would be welcome to adjust the spot WB measure using
Lab values if we know them maybe?

> Of course I may have misunderstood something.
> 

me too ;)

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Re: [darktable-user] White balance on a TrueColor scuadra, using provided Lab values

[KOVÁCS István]

Hi,

If I get this correctly, the card has grey patches as well as colour ones.
The spot white balance tool adjusts white balance only, meaning that:
- after adjustments, grey should be grey (neutral)
- exposure is to be done independently
- colour in non-grey patches, as well as the lightness of all patches are
influenced by the camera profile. See darktable's documentation on that
topic.

Of course I may have misunderstood something.

Kofa

On 5 Sep 2016 11:50, "Emmanuel Lacour"  wrote:

> Le 05/09/2016 à 11:13, Sebastian a écrit :
> > Have you tried the spot white balance preset?
> >
> > See also https://www.darktable.org/usermanual/ch03s04.html.php#
> whitebalance
> >
> >
>
> that's what I use, but after using the spot WB, I check the Lab values
> using the color picker on the same area and values are not the one given
> on the grey card. So I have to manually adjust the white balance, which
> is fastidious with many try/check to be done. I also need to use the
> exposure module to get the right L value.
> 
> 
> darktable user mailing list
> to unsubscribe send a mail to darktable-user+unsubscribe@
> lists.darktable.org
>
>


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Re: [darktable-user] White balance on a TrueColor scuadra, using provided Lab values

[Emmanuel Lacour]

Le 05/09/2016 à 11:13, Sebastian a écrit :
> Have you tried the spot white balance preset?
> 
> See also https://www.darktable.org/usermanual/ch03s04.html.php#whitebalance
> 
>

that's what I use, but after using the spot WB, I check the Lab values
using the color picker on the same area and values are not the one given
on the grey card. So I have to manually adjust the white balance, which
is fastidious with many try/check to be done. I also need to use the
exposure module to get the right L value.

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Re: [darktable-user] White balance on a TrueColor scuadra, using provided Lab values

[Sebastian]

Have you tried the spot white balance preset?

See also https://www.darktable.org/usermanual/ch03s04.html.php#whitebalance


On 09/04/2016 07:51 PM, Emmanuel Lacour wrote:
> Dear DT users,
>
>
> I have a TruColor grey card, and I just saw that when I use the WB
> module to spot on it, the measured Lab values are not the one written on
> the card. Trying to adjust using the sliders of the WB module is a night
> mare :(
>
> Isn't there another way to accuratly adjust WB using this card and the
> Lab values provided by the manufacturer?
> 
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>

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Re: [darktable-user] White balance - difference between camera and camera neutral

[Roman Lebedev]

https://github.com/darktable-org/darktable/blob/master/doc/usermanual/darkroom/modules/basic/whitebalance.xml#L82-L100

On Fri, Sep 2, 2016 at 10:11 PM, Niranjan Rao  wrote:
> Greetings,
>
> Under white balance module, I see two entries for camera and camera neutral.
> What is the difference between these two settings?
>
> Regards,
>
> Niranjan
>
> 
> darktable user mailing list
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>

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Re: [darktable-user] White balance temperature

[Jean-Luc Coulon (f5ibh)]

Hi,

Try a simple experiment : set your camera WB to tungsten, and take an
outside picture. Get the JPEG from the camera. It will be blue... so too
cool.

It is the same in the raw processor, if it is an exterior daylight SCENE
(quite neutral : 5500-6500K)  and you set a warm colour temperature (3000K)
for the PICTURE, it will appear be too cool.

The behaviour is normal: you have to "compensate" so act the opposite as
what you see. You tell the system the temperature YOU decide the SCENE was
et not the temperature you would like the PICTURE appears.

Jean-Luc


2016-03-30 13:12 GMT+02:00 Swee Oon :

> Can someone explain to me darktable's colour temperature settings in the
> white balance module. I thought with colour temperature, the greater the
> value the "colder" the picture will be - but in darktable it's the direct
> opposite. For example, if I move the slider from 5000K to 6000K I expect
> the picture to look cooler, but instead it became warmer. Why is this
> happening in darktable?
>
> --
> cheers,
> Swee
>
>
> 
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>


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