Using curves for White Balance

Watched a vid about using curves instead of the previous way, using the eye dropper, to set white balance.

I have played about a bit, however, without using trial and error, am unsure as to which colour channel to balance the other two too. I am guessing its the one with the highest level.

I have attached some screenies. Which I thought was the same sample point, just changing the channel to balance.
However, now I look at them not at 2.30am but after a couple of hours sleep, I wonder if it is the same sample point. going to post anyhow and go back into the calm, peaceful world of DR and check.

Regards.

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I find that it's better to set white balance with Offset and the RGB Mixer (with Preserve Lum turned off). Once the overall RGB levels are correct, then I use curves for adding contrast. (This all assumes you aren't working with Raw files.)

The only time I use curves for individual color channels is when the footage has a very specific problem. Curves can also help in cases where you have mixed lighting or a situation where you have 3200° lighting contaminating a 5400° setup. Pulling yellow-only in a hue vs sat curve can help to a point.

I would do this very early in the node tree so that subsequent adjustments won't affect the white balance.

Thank you for guidance on what to use where.
Makes much more sense now that its more for a dedicated problem - example footage was two kids under a bedsheet, reading by torch light, with only a small wall mounted light behind, and colour tint.

Another way !

Another way !

5 minutes of my life wasted.

mathematically speaking, if you have already gamma encoded material like the one showed, put the luma mix at 0 and using just the gain control you do a tint/WhiteBalance.
once the image is balanced, use a bit of curves clipping/log control to restore the clipping part.

why making your life so difficult....

mathematically speaking, if you have already gamma encoded material like the one showed, put the luma mix at 0 and using just the gain control you do a tint/WhiteBalance. once the image is balanced, use a bit of curves clipping/log control to restore the clipping part.

It is amazing how hard some of these nutty tutorial people want to make things. The other thing I see is people throwing all kinds of secondaries and stuff very early in the node tree, before the image is really balanced. Not enough people understand the need to start with a very neutral image very early on, then apply the fixes and looks after that point.

There's some really bad advice, almost dangerous in fact, in some of the tutorials out there.

Marc,

Finally tried using the RGB Mixer, with the Parade Scope.
Wow, it makes a big difference. Sure, does one bring up the other channels, or down one of them.
Also damn fiddle to do with just the Magic Trackpad, as it seems one can only click above and below, rather than enter numbers into the boxes directly.

Quick play and it has given the image a much more balanced look. the thing is, you say not to use it on RAW files, yet this is exactly what I am using it on - DNG got from a Canon running Magic Lantern.

Now off to play with Curves and see about contrast. Makes me wish I had not put off using them for all these years in Photoshop, as I would have a more intrinsic understanding of them.

I find that it's better to set white balance with Offset and the RGB Mixer (with Preserve Lum turned off). Once the overall RGB levels are correct, then I use curves for adding contrast

Marc, why the use of the RGB mixer instead of RGB gain controls? Just curious since you've suggested this.

Marc, why the use of the RGB mixer instead of RGB gain controls? Just curious since you've suggested this.

I felt I got cleaner results this way. Red - R-only, Green - G-only, Blue - Blue-only. I have gone back and forth with this, but there's a lot of "it depends" to the method. And sat curves help when there's a lot of contamination in the mids.

It is amazing how hard some of these nutty tutorial people want to make things.

Because the wagon still rolled, (sort of) after they got done re-inventing a thing that resembled a wheel.

And the universe of individuals coming to the pursuit are arriving from every direction. Only a handful from film background, meaning actual emulsion-on-celluloid when we had dye clouds instead of digital values.
When a photographer invokes Photoshop experience - that's a valid standpoint, when a VFX artist tries to adapt their After Effects problem-solving models, that's just the way they model their universe. When an editor simply wants to drop on a LUT or a look filter -- that's the way its done on an EDL timeline.

What the majority of colorists want is a tool that will allow them to rebuild the image, to the point of re-lighting it, re-doing actors' makeup... changing the seasons, time of day, wardrobe...

RGB Mixer stems a bit from the original daVinci as a fundamental approach to extracting the best density from a subject stock, trying to minimize the collateral damage that creeps in when you start borrowing or inventing values from other dye layers or simply pulling them out of one's @$$ (thin air...) what have you. Telecine masking allowed us to build artificial sensitivity into the photo-multipliers or CCD array so that deficient or grainy "blue" could be boosted by sneaking over into the green channel and pretending it was a little further over on the spectrum than it really was, and treating it as extra numbers to plump up a thin channel.

It adhered to the ancient electronic engineer's mantra that "Total Signal-to-Noise in a system is determined at the pre-amplifier stage." Which is true.

If you have access to the RAW source data, it makes sense to go back to the camera. Use the metadata to work out the correct exposure, color temperature, tint, flare... every tool you have available to get it right before you pass it on. This is really where most less-experienced or non-technical approaches fall down.

Digital is not impervious or bullet-proof. It degrades, Noise builds, It has been sampled and while values are numerically forever, there is only a fixed set of them and there is no infinity of interpolation available to offset re-defining what is imagined to be a continuous tonal range. If it ain't there, it ain't there.

Music theory? Everybody knows the octave and the notes. Musicians create great art and play on our emotions with a lot of discrete values, while some instruments don't even have keys or frets or valves that lock in the tone, timbre, and frequency of the sound they make. Trombone, fretless stringed instruments like cello and violin would appear to offer infinite musical continuity -- but still, there is no such thing as E-sharp or F-flat, or B-sharp or C-flat. You can't make these notes no matter what instrument you choose, because they just don't exist. That is one of the mysteries of interval. Go on to the Circle of Fifths. Investigate chord progressions, key signatures... these principles are set in stone and have been for centuries.

That doesn't stop anyone from trying to set themselves up as the person who invented fire, though.
That's just the entitled, solipsist world we live in.

jPo, CSI

Music theory? Everybody knows the octave and the notes. Musicians create great art and play on our emotions with a lot of discrete values, while some instruments don't even have keys or frets or valves that lock in the tone, timbre, and frequency of the sound they make. Trombone, fretless stringed instruments like cello and violin would appear to offer infinite musical continuity -- but still, there is no such thing as E-sharp or F-flat, or B-sharp or C-flat. You can't make these notes no matter what instrument you choose, because they just don't exist.

Paul McCartney was recently on the Howard Stern Show, and he talked for a few minutes about how he can't read or write music at all, and in fact is fearful that if he did learn music theory, it might permanently reduce his ability to write it (which I think is kind of silly). On the other hand, there are also world-class chefs who can cook an entire meal without using measuring cups or a written recipe. A skosh of this, a skosh of that.

What I know about the few colorists in LA who work without scopes is that they have minions who come in prior to the project shipping and these underlings go through the project and make sure everything matches and is legal. In particular, I know of one non-scope colorist who came from a VFX background, and they're still not big on scopes in the world of effects. I think they look on scopes as kind of a broadcast phenomena that doesn't apply to theatrical features.

But in terms of white balance, I can't imagine trying to work without a Vectorscope (or preferably an RGB Parade scope). That will tell you in 1 second if the whites or blacks are contaminated with too much of the wrong color, and also whether it's consistent shot to shot. Without that, I'd feel like I had to run a marathon with my legs cut off at the knees (and I'm short enough already).

Marc - and anyone else, please.

I appreciate I can use the google, however, given your knowledge, do you have any links to tutorials where one can learn to spank the scopes please?

I'm starting to make some progress in looking, seeing what I want to change and now knowing what tool to reach for.
However, it still is lacking, to me. I wonder if better use/understanding of the wiggle lines might be what I need.

Thanks.

Being a member of the "guy coming over from Photoshop" group, I'm curious how you experts feel about the Temp and Tint controls on the second tab of the Primaries panel?
Do you think they're as effective as curves or the other white balance correction methods? Or is there a not-so-obvious problem with using them?

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I appreciate I can use the google, however, given your knowledge, do you have any links to tutorials where one can learn to spank the scopes please?

Steve Hullfish's free Tektronix booklet goes into the subject in great detail:

Using Waveform Monitors as Artist Tools in Color Grading
https://www.tek.com/document/primer/gui ... resolution

Alexis Van Hurkman's Color Correction Handbook goes over the basics as well. And the (free) Resolve manual covers a lot of the basics in the color section.

Being a member of the "guy coming over from Photoshop" group, I'm curious how you experts feel about the Temp and Tint controls on the second tab of the Primaries panel?
Do you think they're as effective as curves or the other white balance correction methods? Or is there a not-so-obvious problem with using them?

Screen Shot 2018-10-29 at 10.26.25 PM.png

Even in Photoshop, "Tint" or "hue" does not effect white balance at all. This control just rotates all the colors around the "color wheel" if you will. The neutral colors are dead center of the wheel and do not change.

The "temp" control simply raises and lowers the Red and Blue channel gain to make the image "warmer" or "Cooler". It is not used for "white balance", though of course, it effects white balance but does nothing to correct anything on the green/magenta axis.

The short and easy answer to white balance is:
Log material: adjust the red, green, blue "offset" if the node is before the transform to your grading colorspace and gamma.

"video" color space material, or REC709 originals:
Adjust the red, green, blue gain controls.

for both methods, find something neutral color, or that you want neutral color in the image and match the RGB levels in the Parade waveform monitor. Or, if you have a good vector scope and eyes, adjust the blob in the middle until it is centered. I'm much better with the first method, but I've seen some very good colorists use the second method very quickly. Of course, if your clip contains a greyscale or chart then it's very quick and easy.

That’s great info, thank you.
I both shoot and edit, so I follow Kodak’s olden days cinematography guidelines and place a Kodak gray card in each lighting setup and roll a few feet of digital film on it. It really helps a rookie like me because I can then start from a relatively neutral place.

I both shoot and edit, so I follow Kodak’s olden days cinematography guidelines and place a Kodak gray card in each lighting setup and roll a few feet of digital film on it. It really helps a rookie like me because I can then start from a relatively neutral place.

I find it's helpful to at least have a grayscale chart so we know what white & black are supposed to be, and what a normal balance should be (assuming a normal color temperature).

Wow, thanks. I don't feel like such a geezer now. And if you read Kodak's documentation they explain how to use a gray card to communicate with the color timer precisely what look you're going for (for instance, underexposing the card when you want the scene printed lighter, and shooting the card under your lights before you add your gels to ensure their color don't get graded out).
Those were the days...maybe?

@bruce:
Great post. A small correction: hue rotate the color space along the grayscale axe, "tint" work in conjunction with the color temperature and it is the "green/ magenta" control.

Yes, offset in log or gain in gamma encoded (or linear light) approximate very well a white balance. I'm used to work in log and I'm so used to look at an image that i don't make the whites "white", but the "gray to skintones" right to the taste of the client. (Balanced, but some client prefer a bit yellow gray and some other don't).

With practice, you will look less at the scope and more at an image.

@bruce:
Great post. A small correction: hue rotate the color space along the grayscale axe, "tint" work in conjunction with the color temperature and it is the "green/ magenta" control.

I did't write that? That's what I meant to write I think for a moment I was thinking of TV set controls where "Hue" and "tint" are labeled interchangeably.

I was thinking of TV set controls where "Hue" and "tint" are labeled interchangeably.

And don't get Charlie Poynton going on "brightness" and "contrast" as labelled on consumer displays. If you are interested, he discusses these items win Chapter 3 of "Digital Video and HDTV Algorithms and Interfaces" ISBN-13: 978-1-55860-792-7 Be warned it is a book with equations and graphs.

Thought I'd get some blow-back on music theory, but maybe I get away with one.

Anyway, yeah... "grey-scale." Scopebox has an interesting option: "HML Balance" puts up three vector displays in a single pane: "High" "Mid" "Low" with a threshold determinant that lets you fine-tune how much of each value zone you want to include in the weighting. Then you can choose which controls you want to use balance/offset to stickhandle the fur balls (herding cats) onto the target of your choice -- usually the bulls-eye of each scope.

And there is Tektronix' "Double Diamond" display that plots G vs. R and (minus) G vs. B. and once you figure out how to "stand the traces up" it all makes perfect sense that that's where your overall balance sits.

The 25-words-or-less best shared opinion I ever heard was in briefing around delivering some dailies for a network show (firm I was working for was souping the OCN and doing best-lights). "Lay it over the center of the scope" and that's all, folks. We were delivering to Encore, Burbank for edit/Online.

Bruce Graham (initial daVinci training) always started with the best black-and-white image and "if it looks weird and not obvious what's wrong, it's your black balance."