White balance, factor or offset?

Archived from groups: rec.photo.digital (More info?)

Hi!
How does the white balancing work? Does the camera derive a fixed offset
for each channel or a factor to multiply each channel with? (I imagine
it ought to be a factor otherwise black and white would become difficult
to do for the cam.)

The reason is I sometimes take picture in difficult lighting conditions
(buildings at night) and I'd like to try separating the white balance
out of the shooting. So, what I plan to do is to shoot one exposure
series with normal daylight white balance and take lots of pictures
of a warmcard set using all the different lamps lighting the building
(also normal daylight balance).

Later at home I'd like to recolor the images of the building
with the white balances of the warmcards.

(Btw, does anyone have an idea on how to do this in photoshop
elements?)

Lots of Greetings and Thanks!
Volker

Archived from groups: rec.photo.digital (More info?)

Volker Hetzer wrote:
> Hi!
> How does the white balancing work? Does the camera derive a fixed offset
> for each channel or a factor to multiply each channel with? (I imagine
> it ought to be a factor otherwise black and white would become difficult
> to do for the cam.)
>
> The reason is I sometimes take picture in difficult lighting conditions
> (buildings at night) and I'd like to try separating the white balance
> out of the shooting. So, what I plan to do is to shoot one exposure
> series with normal daylight white balance and take lots of pictures
> of a warmcard set using all the different lamps lighting the building
> (also normal daylight balance).
>
> Later at home I'd like to recolor the images of the building
> with the white balances of the warmcards.
>
> (Btw, does anyone have an idea on how to do this in photoshop
> elements?)


I'm not understanding your questions. I never heard of a warm card, just
gray card. Normally, just one gray card shot is needed (for each
setting) so why take many card shots? Anyways I'll try to explain what I
understand about the isssue.

The ideal answer to your question is to shoot RAW instead of jpeg mode
but I guess that's not an option for your camera. Still, take a look at
the manual under white balance. There might be a way to set custom white
balance by shooting a card & have that apply to all pics afterwards.

I have full PS and with that, you can Save out a levels setting, then in
another photo, add a levels adjustment layer & Load the saved settings.
I'm not sure if you can do that in Elements. This assumes you want to
use the eyedropper on the gray card to establish RGB adjustments.

I believe certain RAW conversion programs can do their magic on jpeg
files also. That would help you if it's true.

Image > Adjust > Color balance seems the best PS tool for adjusting WB
in jpegs. That has three sliders:

cyan > red
magenta > green
yellow > blue


PS RAW plugin has two sliders:

temperature:
blue > orange

tint:
green > magenta

Temperature seems the most important, tint is secondary. I'm not sure if
those are exactly the colors adjusted, just my guess by looking at it.

I heard mentioned here recently that the orange street lights are almost
impossible to correct WB for. I think it's the blue channel that is
almost completely missing.

Now I have another question. How do people handle this with film?

Archived from groups: rec.photo.digital (More info?)

>
> I'm not understanding your questions. I never heard of a warm card, just
> gray card. Normally, just one gray card shot is needed (for each
> setting) so why take many card shots? Anyways I'll try to explain what I
> understand about the isssue.

Warm cards come in a set of several slightly different shads of a sort of
blue green. By white balancing on them you force the camera to take warmer
photos...sort of like the golden hours near dawn and dusk. There is also a
card for counteracting florescent lights. The concept was designed for
videographers but recently a set was designed for digital still cameras that
also comes with a grey card. www.warmcards.com (I think...maybe no "s" )

Archived from groups: rec.photo.digital (More info?)

paul wrote:

> The ideal answer to your question is to shoot RAW instead of jpeg mode
> but I guess that's not an option for your camera. Still, take a look at
> the manual under white balance. There might be a way to set custom white
> balance by shooting a card & have that apply to all pics afterwards.
Yes, I will use raw (coolpix 5000) but I don't think I'll be able
to come up with good pictures by just trying out different settings.
warmcards are slightly bluish cards which, when used for white balancing
give a red cast. As a beginner I'm simply trusting that they did a better
job than I can do. Normally I would have to white balance with such
a card then shoot then white balance with another or the same in different
light (my motives are lighted with at least two different lights) and so
on.
I am hoping to cut from NoOfWhites times NoOfExposures to NoOfWhites
plus NoOfExposures.

>
> I have full PS and with that, you can Save out a levels setting, then in
> another photo, add a levels adjustment layer & Load the saved settings.
> I'm not sure if you can do that in Elements. This assumes you want to
> use the eyedropper on the gray card to establish RGB adjustments.
Yes, that's what I'm trying. I'll see whether I can do that in elements.


> Image > Adjust > Color balance seems the best PS tool for adjusting WB
> in jpegs. That has three sliders:
>
> cyan > red
> magenta > green
> yellow > blue
>
>
> PS RAW plugin has two sliders:
>
> temperature:
> blue > orange
>
> tint:
> green > magenta

Thanks for the hints!


> I heard mentioned here recently that the orange street lights are almost
> impossible to correct WB for. I think it's the blue channel that is
> almost completely missing.
>
> Now I have another question. How do people handle this with film?
They don't. I have seen this when trying to get a decent picture of Eilenan
Donan Castle in Scotland. I spent two evenenings on it (yellow, incandescend
and halogene lights at the same time) and in the end I got one picture which
as a novice I could barely live with. The colours of the postcards in the shop
were totally irrational compared to that.

This easter I'm having another go at tower bridge which is much more complex
and would be impossible to shoot like I did the castle. (Last time I took
about 150 pictures with none really satisfying me.) That is why I think
about taking the colour balance separately from the motive and combine them
at home.

Lots of Greetings!
Volker