About colour correction and oscilloscopes

[ejmillan]

I have low-quality home video footage in incandescent lighting.
I wanted to correct as much as possible the yellow cast of this video.

I started reading about colour correction and colour grading, I watched some tutorials but they were not helpful because they talked about specific tools from commercial video editors, using adjustment layers or even moving masks for local adjustments quasi-automatically, but with the use of these tools there is little talk about manual adjustments.

Shotcut has a specific provision for colour management. In it are visible different graphics that can help with the task of colour adjustment.
I never used my time to learn about these graphics and what they represent, but now I think it would be good to understand a bit about their purpose.
In my video, I would like to eliminate that yellowish-orange tone that floods the whole scene, but at the same time, I want to keep the natural flesh tone of the people.
I probably need a combination of filters.
I know this might be a bit of an extreme job and might not be possible. Also, the video in the badly lit areas has noise (grain), but that is another problem to be solved later.
It’s not that I’m lazy that I haven’t looked for the information (here in the forum or outside) but I didn’t find what I’m looking for.
Does anyone know of a resource or information as a practical (not theoretical) guide to understand a bit about these graphics?
What is the purpose of the Video Zoom included in the Video Vector?

It is a dense subject I admit it.
Thank you in advance for any help or advice.

[Austin]

@ejmillan

Shotcut has […] different graphics that can help with the task of colour adjustment.

I have a very unsatisfying reply for you, which is so empty that I normally wouldn’t reply at all except that no one else has.

Those graphs can tell you a lot about the color and brightness of the video. But without a target, that information isn’t quite as useful.

For instance, if there was a gray card reference in the scene before the action started, then looking at the color cast on the gray card (which by definition should not have a color cast) would tell you exactly how much modification needs to be done to fix the scene. Without a target or a reference, the best that can be done is tweak things by eye until it looks “good enough”.

The other place those graphs come in handy (gray card or not) is in maintaining consistency across scenes or multi-cam cuts. If the footage has filters that set similar saturation and brightness across cameras, then the jump cuts will look quite seamless. This prevents Camera 1 from looking noticeably darker than Camera 2. The graphs (vectorscope for color and waveform for brightness) provide an objective way of knowing how close two scenes really are.

@ejmillan

I would like to eliminate that yellowish-orange tone that floods the whole scene

In the screenshot, there is a white window frame that is not over-exposed (meaning it still has full color information), so you could possibly use it with the White Balance filter color picker to turn video-white back into true-white.

@ejmillan

I want to keep the natural flesh tone of the people.

If the White Balance filter wrecks the skin tones, then a compromise with the strength of White Balance may be needed. Or, sometimes the Old Film: Technocolor filter can modify just the red channel in a way that works well for skin. I often use this filter with certain Panasonic cameras that are a little heavy on the red tones. A better way of course would be a Hue-vs-Hue or Curves filter, but Shotcut doesn’t have those yet.

@ejmillan

Does anyone know of a resource or information as a practical (not theoretical) guide to understand a bit about these graphics?

In one convenient place, outside of a paid class? Unfortunately, no. The information is out there, but scattered in a thousand random places needing to be pulled together. I would be interested as well if anyone knows of a solid start-to-finish color theory and management tutorial for free online that I could recommend to others. I had to pay for my education. Speaking of which, this book is very good in regards to color workflow management. It focuses more on photography and printing than video, but the concepts of light and color manipulation are pretty universal:

https://www.amazon.com/Color-Management-Quality-Output-Working/dp/0240821114

@ejmillan

What is the purpose of the Video Zoom included in the Video Vector?

It basically lets you see RGB or YUV values up close. For instance, if you’re expecting video to be MPEG range (16-235) but there are 0 or 255 values scattered around, that’s a good hint that the range was signaled wrong and needs to be overridden. It can also be useful as a generic color picker for setting up color clips or masks.

[ejmillan]

I really did find your response helpful and I thank you for it.
And yes, you have given me some guidance as at least I know what purpose or what is necessary to take advantage of all those oscilloscopes.
Even if it is not a direct solution it is equally valuable.
The truth, even if sometimes not to my liking, is the most honest thing to offer.
The camera was a Panasonic with VHS-C tape.
I tried to use white balance but it was a bit strange.
Colour correction was a headache because, firstly, I didn’t know what I was doing, and secondly, because the results were worse than the original image.
If it had worked, I wouldn’t even be asking, haha.
Thanks @Austin

[kagsundaram]

@Austin

I often use this filter with certain Panasonic cameras that are a little heavy on the red tones.

I use Panasonic cameras; this is a very useful heads-up for me to look into.
Thanks.

@Austin

A better way of course would be a … Curves filter

RGB-curves, Saturation-curves

The three-wheel color grading is nice, but doesn’t give enough freedom. Could it be possible to have curve-based color correction tools? Similar in Gimp, Blender, etc. Thank you for all your work!

Curves filter possible?

One thing I miss during colour grading is using curves. Is this particularly difficult to implement as a filter - I noticed it wasn’t listed on the roadmap page. I have used levels, but with just three points (shadow, mid-tone and highlights) to modify the separate RGB and luma channels makes it harder to achieve a personal film-like contrast, compared to using multiple handles on the curves. Another thing that is useful is having a curves-specific eyedropper tool that, when clicked in the monit…

@kagsundaram

I am more comfortable with the “transfer function” conceptualization, as exemplified by the “Color:Curves” tool in The Gimp image editing software.
I have been wondering if it would be possible to build a filter which used this conceptualization, this set of controls (and maybe even the same software; The Gimp is Open Source) as a front end for the same underlying filters used by Color Grading and Contrast.
That would be a whole lot easier for me to use, and I suspect for many others like me.

The cheerleaders shout “Curves!”
…and the crowd shouts back “CURVES!!!”

[bentacular]

Just from personal experience and learning about color correction for a year. Surprisingly, most color cast issues can be fixed without fiddling with specific colors at all.

That’s why I start with white balance. If there is a spot in the video/picture that is 100% white, fixing that spot and making it 100% fixes a lot of the casting issues. This will be your connection to reality. Though most pros use a gray card, which is actually 18% and place it in the scene somewhere. You can buy cheap ones on Amazon: https://amzn.to/2O2jW87. Some use paper towels. Establishing white balance can save loads of time color correcting. For this, I don’t use any scopes.

Then, once I can guarantee white balance is correct, I fix exposure. For that, I specifically only use Video Waveform. I do what I specified in my tutorial.

Once those 2 are locked up, I do final touches on color casts, if there are left that white balancing didn’t fix. For that I use the Video Vectorscope. The direction of color is specifically highlighted in this scope.

I’m simple, so that’s all I do

[kagsundaram]

@ejmillan

Colour correction was a headache because,

Color correction is always a headache.

[ejmillan]

My problem is not with future recordings.
These videos are recordings made with a Panasonic VZ9 camcorder.

My first camcorder also meant my first recordings, so the imperfection is present in those recordings.
However, these videos also document a very dear past.
Thanks for the tips. The grey card wasn’t there but I can fall back on the simple things as you rightly say.
I’m so used to watching tutorials with colour enhancements on high quality files that the results I got on my videos seemed poor. I’ll keep trying

[ejmillan]

Wow, that was a morale booster. Maybe I’ll get lucky on the next attempt tomorrow.
Thank you very much for all the comments.

[bentacular]

Once the videos are recorded at a certain quality, you are pretty much limited to how well it will look. You can make it look better, but not as good as those tutorials where they pre-plan the white balance and exposure. Some are just going to look like crap, but at least better than the original.

[Austin]

Given a VHS-C source, if the colors are dull or muted, try adding some Saturation once the White Balance is figured out. Or turn Saturation down if the colors look like giant patches of vibrant solid colors with no tonality or gradients. On the vectorscope, Saturation changes how far the spikes will extend from the center of the circle.

[ejmillan]

I made a montage for visual comparison with various settings.
Above left is the original video.
To its right, I placed the following filters in order:
White Balance
Old film: Technocolor
Noise reduction: Wavelet
Sharpening.
Below left I tried a change of order and placed first the Technocolor filter and then the white balance (it doesn’t work any better).
Bottom right I did not use the Old Film Technocolor filter, instead, I used the Saturation filter.

Once I had reviewed the footage and compared the different scenes, I wanted to take some stills.
For this I disabled proxy and preview scaling.
Then I noticed that the video with the wavelet noise reduction filter worked differently between the old Technocolor film setting and the video with the saturation filter.
You can see how the inside of the cabinet has noise (Technocolor) and yet the wall and scale models have a better sharpness in that setting.
In motion, this is almost not visible, but I found it curious and here I comment on it.

Either way, the colors look more natural than in the original video. Thanks for the tips.

[kagsundaram]

@ejmillan

Then I noticed that the video with the wavelet noise reduction filter worked differently between the old Technocolor film setting and the video with the saturation filter.

The NoiseReduction:Wavelet filter is a strange and wonderful tool.

@kagsundaram

I am delving into the complex interaction of the ReduceNoise:Wavelet and the Sharpen filters.

Not only is the interaction with Sharpen a complex one, the interaction with a following Contrast filter is also complex.

I found that there are multiple “sweet spots” for the Contrast, each spot only 0.1% wide, between settings that yield horrible big blotches.

It must be an unavoidable effect of the algorithms and the digitization, so I am not complaining.
I simply point it out so that others will know that when using this combination, fine-tuning upwards past the “That looks terrible!” point can sometimes yield good results.

[st599]

Re: Skin Tones

If you look at the vectorscope, it has targets for the colours seen in a set of 75% and 100% colour bars (white and black would appear at the centre of the scope). The scope is achromatic at the centre and increases in saturation the further out you go.

There is then another, fainter, line with no targets on it. That is meant to match the average skin tone pigment under reference lighting (there are slight variations and it changes slightly with temperature).

If you have a close up of a person, there should be a spike along the line, if not, you can tell if the colour is too red or too blue. You can also use it to match saturation between shots either side of a cut.

[ejmillan]

Thank you so much for sharing this information. I will definitely take a closer look at this.
I put this project on hold for a week because I wanted to also start a series of short videos on the practical use (with some examples) of Shotcut audio filters.
I have a lot of videos to improve and I don’t want to rush into doing a quick and bad job, so it may take me longer to do this than I had anticipated.

[ejmillan]

There seem to be many variables to understand this and it doesn’t seem like a simple thing.

[chris319]

I’ve set up TV cameras hundreds of times over the years. We, and the high-end colorists I know, would never use a vectorscope to set flesh tones. There are too many variations in flesh tones for a vectorscope to be of much use.

If you have an achromatic object in the shot such as a neutral white or gray object, white balance on that using ShotCut’s white balance tool. Failing that, try adding a little blue and eyeball it. It looks like the camera was balanced for a bluer light source than the light the scene was shot with. First make sure your monitor is properly calibrated.

[kagsundaram]

@chris319

First make sure your monitor is properly calibrated.

When my proverbial ship comes on, next on my list after a high-end Nvidia card that supports four or more monitors is an old used Conrac CRT monitor off of eBay, the calibratable standard for TV color for decades.

Sure, it maxes out at 640x480; I’ll mostly use it for TTY Terminal amber-on-black, but when I want to see my video in calibrated color, it will be there waiting.

[chris319]

Do you have a good color checker for your monitor? I use the XRite i1.

An old Conrac CRT monitor? Really? I don’t know what it could do that a modern monitor couldn’t. Will you have an analog signal to feed it?

[kagsundaram]

@chris319

An old Conrac CRT monitor? Really?

It’s what I am familiar with, from back in the day, when we built the 48-channel PP1 “Mickey Mouse” console at Harrison Systems that replaced the “Fantasia” console at Disney Studios, and I wrote the software for the Input, Group and Equalizer modules. The automation and VU/PP meters were displayed on Conracs, because that is what was spec’d. We had no problem driving the Conracs with the controller card that we used, driven by a Zilog computer using digital interfaces I designed.

[kagsundaram]

@kagsundaram

We had no problem driving the Conracs with the controller card that we used, driven by a Zilog computer using digital interfaces I designed.

It’s been so long, I had to research what the inputs were on those old Conracs. However, whichever input system those used, Conrac did put an SVGA interface on some models, and those are what are on my eBay “Watch” list.