LAB Color Foundations Part 3: Is it effective for initial contrast adjustments?

LAB Color Foundations Part 3: Is it effective for initial contrast adjustments?

December 3, 2014

Explore several types of source footage to determine which one are best suited for working with LAB color in DaVinci Resolve.


Series

Day 3: 25 Insights in 25 Days Holiday Marathon

Working in LAB Colorspace: Is it effective?

In our series on LAB color in DaVinci Resolve we’ve been looking at the theory of color contrast expansion in LAB. We’ve also looked at some of the limitations when it comes to drawing curves for LAB Color in DaVinci Resolve. Now let’s try applying the basic contrast expansion ‘formula’ to a variety of shots and see what we think?

Recap: LAB Colorspace – The Rules

As you watch this video Insight, keep in mind all the shots I’ve selected are either RAW (developed into a flat LOG profile) or recorded as LOG.

Remember, the initial rule of thumb is that we want to start with images that are flat and colorless—since that’s what the ‘Photoshop guys’ say tend to be the best candidates for these types of LAB color corrections. Later in this series, we’ll look at LAB with full-color images and see if we agree with that analysis when color correcting moving images inside the LAB colorspace. But for now, let’s keep to the recommendations which for us video peeps—LOG style images clearly fit the recommended image profile.

Recap: My Basic Node Structure

Also – one of the restrictions I’ve placed on myself for this Insight is to keep our LAB ‘moves’ contained within a single LAB node. And because of how ‘contrast’ and ‘saturation’ work on all three LAB channels, I’ll be avoiding them and sticking to working mostly in Curves. In an upcoming Insight, I’ll explore alternate node structures that will open up the tools we can use in Resolve—at the expense of slightly more complicated node trees.

LAB Color in DaVinci Resolve: Beyond Still Life

As mentioned in earlier Insights, LAB colorspace has traditionally been relegated to still life photography of natural expanses of landscapes. The concept being that LAB is very good at expanding color contrast in the Reds / Orange / Yellow / Green side of the spectrum.

As a colorist, restricting LAB to just those types of scenes doesn’t make it a compelling colorspace to spend time developing my skills. Outside of Nature documentaries, the stories I’m hired to help improve involve people.

And it just so happens, faces and skin tones tend to fall in the same range that LAB is most suited for effecting.

For this Insight, I’m selecting shots that feature people and lots of skin tone, to see if it gives me results that would be difficult to replicate in the RGB colorspace. I’m pulling in shots that I’ve previously graded using our default RGB colorspace and comparing those results with my new LAB toolset.

Treating a LAB node like a LUT node

One point I make in this Insight is that I’m starting to put the LAB colorspace node at the same point in the node tree like I do when I’m using a LUT. Not surprising, since we’re using both of them here to perform the exact same operation—expanding contrast and adding color!

If you’re not familiar with my approach to LUTs, watch this series on working with LUTs in DaVinci Resolve and you’ll be up to speed on my philosophy in no time.

– pat

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Comments

9 thoughts on “LAB Color Foundations Part 3: Is it effective for initial contrast adjustments?”

    1. Well – one thing to keep in mind, the input and output of every node is always RGB. So yes, any grades we do with a colorspace manipulation should work just fine as a LUT export. But I’ll be sure to do a formal test and make sure nothing wonky is going on is this regard.

  1. Could try an example comparison of a clip with a oneshot chart before and after both the LAB and RGB saturation adjustments? First balance the chart and get all the swatches lined up on the vector scope targets (scope zoomed 2x / pre saturation). The vector scope targets would give us a good way to see how color is affected by the 2 methods. I can shoot something for u if you don’t have a oneshot chart clip.

    1. Greg – that would be awesome if you could shoot a chart. I’ll be happy to test. Just keep in mind – LAB is not about being definitively better or worse than RGB… it’s a choice. And our decisions will be based on creative goals as much as the technical evaluation of test footage. One job may be perfect for LAB while another… it could be the absolute wrong choice. The question I’m trying to answer in my mind… how to approach LAB so we can make very quick—but informed—decisions about if it’s an avenue worth pursing with the job in front of us today.

      1. I agree but balancing the removes the camera color biases pre saturation. To balance the chart I imagine you would be doing some hue vs saturation adjustments in rgb though. Are there any elements/colors you would like to see in the chart footage? skin tones, greens, etc?

        1. Skin tone, red and green apple would be cool. One concern I have is the ability to control vibrantly colored images. It’s why I’m still only feeding LAB log or raw footage – to give it its best shot at being useful. Later I’ll experiment with footage shot into Rec709 and see how it performs.

  2. Could this be reversed to tone down a super saturated image? I know there are numerous methods but just curious, as it would also decrease color separation as well, correct? Also, curious about how this works w skin tones due to its aggressive contrast expansion, aside from very tan as in the example. Another really great one. Thx Pat!

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