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Author Topic: White balancing using Levels  (Read 1540 times)

Dinarius

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White balancing using Levels
« on: May 10, 2018, 08:16:20 AM »

I've been playing with DaVinci Resolve lately for video editing, and it's white balancing facility (particularly its Scopes window - a diagrammatic rendering of the amount of red, green and blue in an image) is superb. Basically, you simply equalize the amount of R, G and B while looking at the Scopes window and you're pretty much in the ballpark.

This got me thinking.......

Like most people, I use a neutral card in critical situations. This gets me in the ballpark, and I then tweak Kelvin and/or Tint to fine tune the result.

But, try this.......

In Levels, click on the Red channel. Now move the highlight slider in to the left until an area of highlight in the image starts to show highlight warning. Move it back to the right just enough to remove the highlight warning.

Now do exactly the same thing for the green and blue channels.

Use Alt/Levels Reset to compare before and after.

Better still, create a New Variant before you start. Correct one using this method and the other using the White Balance tool. Then compare.

Notice any difference? I do.

This is about as close as I can get to a DaVinci Resolve-type white balance.

It may be old hat to some of you, but I hadn't tried it before. I really like what I see, but I could be imagining things! :)

Note:

1. This has no effect on the RGB Levels tab. It's still zeroed out. You're still free to edit overall contrast using it.

2. It has no effect the White Balance tab. It will still read as Shot.

Any thoughts?

D.
« Last Edit: May 10, 2018, 08:22:35 AM by Dinarius »
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kirkt

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Re: White balancing using Levels
« Reply #1 on: May 10, 2018, 10:33:24 AM »

I think performing color balance this way perhaps enhances what you see because it changes the white point and adds overall contrast to the midtones and highlights.  In a layer-based pixel editor, you could change the blend mode to "Color" and remove the tonal shifts.

The same operation can be done with Curves, and you can adjust the color balance differently for the highlights, midtones and shadows (arbitrary delineation of each region) by deviating from a linear curve.  Although this deviates from channel scaling a linear image for white balance, it is an artistic decision, so whatever works!  You can also perform split toning, etc.

kirk
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BartvanderWolf

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Re: White balancing using Levels
« Reply #2 on: May 10, 2018, 10:50:00 AM »

Any thoughts?

Hi,

This only works with linear gamma images. When using it on Gamma adjusted images, there will be unwanted color shifts all over.

Cheers,
Bart
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brieisenberg

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Re: White balancing using Levels
« Reply #3 on: May 10, 2018, 12:10:40 PM »

If I understand what you are saying correctly, then C1 has an option to do this automatically (or at least get you in the ballpark to start with). In the preferences tab there is an option for auto levels.  It defaults to RGB, which only adjusts shadow and highlight point.  You can change the setting to "red, green, and blue channels" to have it behave in the way you describe.  Photoshop also  does this with its levels tool, but you have to hit option and the auto button and set parameters from there
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Jim Kasson

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Re: White balancing using Levels
« Reply #4 on: May 10, 2018, 03:06:20 PM »

Hi,

This only works with linear gamma images. When using it on Gamma adjusted images, there will be unwanted color shifts all over.


True enough, Bart. And some primaries are better than others for simulating visual adaptation.

Jim

FranciscoDisilvestro

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Re: White balancing using Levels
« Reply #5 on: May 10, 2018, 07:51:01 PM »

That is basically the way white balance works. Adjusting the levels per channel is equivalent to multiplying the values of each by a scalar factor. Now the argument here may be if you do it before or after demosaicing and rendering (always in linear gamma), but it practically does not matter as long as you don' t clip values.

A simplified version of what white balance does:
Temperature: Adjust R & B channels in an inverse way (as it lowers the R levels it increases the B levels and vice-versa)
Tint: Adjust the G channel (some implementation impact the R & G channels)

As Bart said, it works with linear gamma images and it is also the reason why you should white balance before capture if you shoot directly jpg or any other output / gamma encoded format.

As a final note: using programs such as DCRaw or Raw Therapee, you can adjust the levels directly on the raw data before demosaicing

dchew

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Re: White balancing using Levels
« Reply #6 on: May 14, 2018, 10:47:27 AM »

Note that in preferences, you can set the levels tool to essentially do this. Channel mode has two options: RGB Channel and "Red, Green, and Blue Channels."

If you select the latter and click "A" to auto levels, it will do something like what the OP outlined. I don't generally like the result partly because of Bart's point, but it is interesting to try once in a while.

Dave
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gdh

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Re: White balancing using Levels
« Reply #7 on: May 18, 2018, 11:30:05 PM »

Dave Chew--awwwesome images on your website.  very impressed

dchew

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Re: White balancing using Levels
« Reply #8 on: May 19, 2018, 08:52:30 PM »

Dave Chew--awwwesome images on your website.  very impressed
Thank you very much.
 8)

Dave
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