White balance question


#1

Hello,
I was wondering if there is an easy way in RT how to obtain the best spot for white balance. Sometimes I find a picture problematic and in order to find the best spot for WB I must spent just too much time on looking for it (which is an area that has similar or close all the RGB values)
In gimp/photoshop it gets easier because I can create a new, blank layer, fill it with middle gray, set its blending mode to ‘difference’ and use threshold to obtain it (see: https://patdavid.net/2011/06/getting-around-in-gimp-color-correction.html).

Is that technique possible in RT? I know that 'retinex” has some masking capabilities, but it is complicated tool. I’m currently experimenting with it and wavelets – but with no luck.
If it is not possible, would it be difficult to implement such a nice feature? It would be really helpful and save rt users a great deal of time.

Another idea would be to set a white balance according to skin tones. Alex from magic lantern project implemented it once in ufraw (https://www.magiclantern.fm/forum/index.php?topic=9469.0)

Also, i’m crossing my fingers for @jdc and his WB ‘robust’ research and work.

Although I have Photoshop and Lightroom, I keep coming back to my favorite duo – rt + gimp!
Thanks,


#2

Hi @kazah7,

Our favourite Hawaiian (hi @harry_durgin!) has worked quite a lot on how to find proper balance from a variety of objects, and his work resulted in the useful http://weeklyedit.com/lab-reference-chart/.

Have fun!
Claes in Lund, Sweden


#3

@kazah7 Good question and ideas. I have done some reading on wb myself because it is so fascinating. There is lots of research being done that has resulted in numerous theories and methods. Some references for you to check out if you haven’t already:

Or search this forum: I see more than 40 results pop up using wb or white balance with #software:rawtherapee.


(Desmis) #4

As I already mentioned the white balance is something complex, often subjective and mostly wrong!

A few years ago, I made a summary that was translated into English
http://rawpedia.rawtherapee.com/Color_Management_addon#White_balance

The only thing that is pretty much right is the matrix operation between the illuminant and the base color found on the spectrometer.

But in the majority of cases, the problem is that we do not know the iluminant - if we knew it, the problem would be almost solved, nor the spectral color of the subject (flower, face, sky, etc.).
We are faced with a problem where there are more unknowns than equations

The alternative solutions presented in eg Photoshop or other software like Ufraw (patch for skin), are only work around and do not solve the problem.
But they give the impression of doing something serious, omitting a parameter from the equation

I do not neglect these solutions but in most cases they are false.

Creating a target gray mask (or other hue) is a solution to target / reach a color, but is generaly obsolete for the white balance.
Indeed the gray that we will target on the image itself depends on the coefficients of the white balance that is applied to the red, blue and green channels.
So in French “c’est le chat qui se mord la queue”; it’s the cat that is biting its tail.

It is the same if one uses the skin, whose variation of hue is close to 1 radian, which is enormous.
As I said the real solution is to take the picture, as would Alfred Hitchkock who always appeared in his films, putting a gray chart incorporated into the scene.


#5

:+1: for Hitchcock and being the voice of reason.


#6

Hitchkock, being the voice of reason and ποίησις.


#7

Thank you for your explanation and link. I must have missed that … As you said - it’s quite complex. @jdc @afre @Claes I’ve just purchased ExpoDisc II (https://www.expodisc.com/products/expodisc-2-0). I will let you know how well it works. :slight_smile:


#8

@kazah7 Please do tell how the ExpoDisc works for you.
I own a similar contraption, and honestly, I cannot decide
whether it is useful or not :thinking:

Have fun!
Claes in Lund, Sweden


#9

Sure, I will tell you if it is worth buying or not. Unfortunately, I have to wait another week for it - it was out of stock.


#10

I use a clean styrofoam cup if one is handy and I feel adventurous :slight_smile:.