Color correction card / flat color profile interoperation

[Dimedrol]

Hello there!
I'm a newbie in video production (with some experience, indeed )
and definitely newbie in color grading.
My software: DaVinci Resolve 17.

ATM I'm curious on the following:

I have a video footage in flat (or e.g. LOG) color profile.
If I use color correction card,

making my video, should I use
color conversion function, e.g. special LUT for transforming LOG to Rec709?
Or I can just match colors from the color correction card?
(DaVinci Resolve can do it - select card and draw the rectangle above the card on video)

So if I have color correction card - do I still need "remove LOG" with special LUTs?

Another question follows this one:
What if I have a footage, taken without LOG/Flat profile?
E.g. on smartphone (not FilMiC Pro or similar!) or old GoPro without ProTunes?
Can color correction card help me in adjusting (often, oversaturated colors on smartphones) stuff for my postprocessing?
Or, if I have smartphone footage - it is definitely unrecoverable garbage...? ;-)

Any ideas will be much appreciated!

 

[apekkpul]

I would use Resolve's own color management to transform LOG to Rec709, see a tutorial:

(The color management typically works great, but sometimes you will get better color with LUTs...)

However, you may still have have a color cast, so you may need to correct that first e.g. by using a color checker card. I haven't used those cards, but I assume that Resolve doesn't automatically fix over-saturation but you need to manually adjust for your taste.

 

[Off The Mark]

I have a video footage in flat (or e.g. LOG) color profile.

I don't understand.

Are you recording in flat profile? Or are you recording in LOG profile?

Or do you mean that SOMETIMES you record in Flat profile, and sometimes you record in LOG profile, and your use both (flat and LOG) clips on the same timeline?

Personally I am a big fan of using Resolve Color Management and Davicni Wide Gamut in the Color Management settings on the settings page.

Then I right click on the files that are recorded in LOG profile and for Input Color Profile I choose the gamma it was recorded in (for example: for Sony, S-LOG, for Panasonic I select V-LOG, etc.,).

But if you are using clips recorded in both Flat and LOG (and let's say some iPhone footage, too), then make sure those clips have their Input Color set as Rec.709

Then I also use the HDR tools to do grading. I highly recommend them because they tend to avoid oversaturation of the image when adjusting brightness (something the old RGB wheels tend to do).

Regarding LUTs:

I am not a big fan personally, but they can come in handy.

I would NOT use a LUT on Rec.709 footage (like Flat profile or iPhone footage).

If you use a LUT on LOG footage, then I would use it as the SECOND (or third) node in your node tree, not the first.

In the first node I would use the HDR tools to adjust the luminance.

The reason is if your footage is pretty brightly exposed, if you apply a LUT and it clips the footage, nothing you can do in the footage AFTER the LUT can recover the clipped highlights.

But if your footage is bright but NOT clipped, then you can bring the exposure down in the first node, and THEN apply the LUT.

Regarding Color Card and NON Log Footage:

Yes, it can help a bit.

Usually with 8-bit footage, you are limited in the adjustments you can make before things start to look bad. People say that the footage "breaks / falls apart."

Again, even though 8-bit footage is NOT HDR footage, I do suggest trying to work with the HDR panel in Resolve.

Also, this is where the vectorscope can come in handy in Resolve. You would use it to help you better visualize which colors are over-saturated / under-saturated, and whether you need to rotate the hue or not.

I would suggest you look at this video by Gerald Undone, in particular the section on how to Color Match Manually (it starts at the 5:09 minute mark of the video)

--
What Middle School Is Really Like:

 

[Entropy512]

A color correction card isn't really good for reverse engineering unknown tone curves/transfer functions - too few patches. It kindasorta works, but not well for this purpose.

It's much better for identifying the gamut of an image once you are able to linearize it.

Reverse engineering an unknown transfer function is better achieved by taking a series of bracketed shots of a gradient and feeding it to OpenCV's CalibrateDebevec function.

 

[Dimedrol]

apekkpul, Entropy512 and especially Off The Mark - thank you for such informative answers!