Color Correction

I just posted a new, edited response, adding in Section 4 ... doing the also necessary matching between saturation levels of the chip charts for each camera.

With the hue response nearly equalized between cameras, for both hue and saturation, along with some tonal correction, this gets you a long way to matching the cameras adequately.

Note, you don't need a perfect match between images from the different cameras. Just close enough that when going through the sequence, the eye and mind are never distracted by changes.

Notice my Hue instructions suggested moving the box to an in-line spot for each hue, but only about halfway out? That seems to help in a number of ways. Nothing is oversaturated, no artifacts, and the cameras are mostly neutral.

Which makes it easy to either raise or lower sat a small amount per clip for better visual perception matches.

Running the sat clear out to the boxes, for me, has always induced trouble.

Thank you so much for all this great information Neil. This will definately help my work flow. 

(Note: edited, adding in Section 4 on matching saturation, which I forgot to list in the first go through of this process.)

As to the old NTSC color space, as noted before, I don't know of a colorist ever mentioning that. And I've seen the standard delivery specs they've used for various US broadcast and streaming systems, always using bog-standard Rec.709.

I do know that they want to make sure that "legal" is used for all YUV (technically Y/Cb-Cr) media. 

Some newer cams, from Panny & Canon especially, along with some 'action' rigs like GoPros ... allow the user to set a "full" range encoding process even though by standards it should be limited/legal. And that can be a right bear at times, as then it isn't showing the same image depending on the app and monitor settings.  I think some apps will ignore the 'full' on a YUV clip, display it limited. Others display it full.

And it shouldn't make any difference in the amount of levels recorded, only the way they are encoded ... I've been told over and over by color experts. But still ... it "sounds" like there's more there, right?

So I'll give a couple ways to work things in Premiere Pro as it stands in 23.6. The below is for working in broadcast standard Rec.709/SDR.

1) Issues with camera full/limited settings

For clips that seem to be full range for YUV clips, there are Lumetri presets for conversion of Full to Limited and Limited to Full. Select the clips in the Project panel bin, and then drag/drop the appropriate Lumetri conversion preset onto them.

This is most prominently an issue with GoPro's, and some Panny and Canon cameras at this point. Some iPhone media also.

2)  Color balancing including for shadow tint

Many scenes not only need a white balance step, but have shadows with a tint/cast to them. For the shadow cast/tint, go to the Creative tab of Lumetri. Slide the 'Tint Balance" control down, to the left, to about the 20% area (around -65 for numerical setting). This sets the 'pivot' point well below midtones. Now adjust the Shadow tint wheel until the shadows balance out on the scopes.

In fact, you can use this control for both white balance (using the Highlights tint) and shadow cast control. Note that has been done with this image.

And again, if this correction works across multiple images ... copy the Lumetri instance in the Effects Control panel, select the clips in the Project panel, and and paste the Lumetri effect onto them. Bulk corrections any time, any place you can, speeds the work along.

3) Matching Hues between cameras

Quite often, one of the biggest difficulties in matching cameras is they record hues differently. The various major tones ... red, green, blue, cyan, yellow, and magenta ... will 'sit' in a different place on the Vectorscope for one camera than another. Given the limited targeted capabilities of Lumetri, this will cause a ton of time and frustration in shotmatching a sequence.

If you have apples to apples shots to compare, this can save a MASSIVE amount of time. By this, I mean something where the cameras shoot the same scene from the same angle with the same lighting. Such as of course, a shot of a chip-chart. The DSC Labs ones are the gold standard, but even the Xrite Passport video card works.

And if they have this for every scene, great ... but even if it's just once for the project, for every camera, you're miles ahead.

Either that, or if some time in the project, the cameras simply have the same scene from the same angle, with a range of hues, this can be made to work. I'll start with the instructions for the chip charts.

• Make a quicky sequence of just the clips with the chip charts.
• Start with the main "A" cam, in the color workspace. From the ECP controls, make a mask small enough to show only one chip at a time, and set the White chip to maybe 90IRE, the Black to around 5-8IRE, and the middle gray to around 40IRE.
• Now go to the Curves tab, the Hue v Hue control. Pick a color to start, and work around the color wheel. Say starting with Red, working clockwise ... click the Hue v Hue color picker, click in the Red box to select that color while holding down the Ctrl/Cmd key to get a bigger sample area, then use the mouse to grab the center of the three control points, and move it up or down to place the Red tone inline with the Red/center axis, and about halfway between the center of the Vectorscope and the outer limits of that color and the Red box. Once accomplished, delete the other two control points.
• Do this with each color in turn, working around the Vectorscope's Hue axis.
• Once complete for one camera, do this same process with the others.

4) Matching Saturation between cameras (added in edit of the prior post)

After doing the above steps, you're much closer to matching than you started. But it does also need the following.

Similar to the work in the Hue v Hue, now go to Hue v Sat.

• As before, use the mask on the Lumetri effect in the ECP to see one box at a time.
• Start with a color, and go around the ring. Select the eyedropper and click (while again, holding down the Ctrl/Cmd key) in the color box in the monitor to get a sample point on the Hue v Sat curve.
• Adjust the middle control point to somewhere around the halfway point from center to the box of that color.
• Work around the 'wheel' as before.

Now I would suggest naming each Lumetri instance for the camera it does Hue corrections for. 

Select all the clips from that camera in the Project panel, and apply the copied Lumetri instance for that camera.

The above most likely will dramatically alter the images from the cameras closer together. And as the remaining differences are mostly about tonal changes or white/shadow balance, for each scene, the time needed to do basic shotmatching is also dramatically reduced.

You could save the above Lumetri presets if it's a job that may add additional clips, then dump at the end of the job. Or not, your choice.

You can also when correcting scenes, match the first clip of each camera ... using a frame with as close to the same image as possible ... then copy/paste the Lumetri to other clips on that sequence directly on the sequence.

As the NTSC specific, 1953 era color space is a bit ... tilted ... kinda an odd thing, really ... with the wider color spaces coming into use now, I doubt they'll add that rather narrow (comparative) space.

I work for/with/teach pro colorists. So I am around a lot of deliverables discussions. And none of them ever talk about NTSC color space. They deliver Rec.709 or some form of HDR.

They do tend to work with outboard scopes. And often, they run the signal to a second computer that actually runs the scopes. And will have the 7.5 IRE black line on that scope.

I do recall being told that a proper video "legal level" file in full-on Rec.709 (like Premiere uses) should satisfy the 7.5 IRE black need. But haven't tested that.

I know many colorists simply work in limited/legal for nearly all SDR/Rec.709 work, and don't have the 7.5 IRE line set in their scopes. So I've always assumed, it must work ok.

I do wish that the Pr devs would give users the ability to set the graticles ... the 'tell' lines on a scope ... to our needs. No matter whether they are SDR in PAL or NTSC, or some form of HDR. I've asked for that for years.

I've also pushed for either expanding Lumetri dramatically, or bringing back (in essence) SpeedGrade. To no avail. Ah well.

Lumetri can to a ton more than many are aware, especially if you know how to use applied presets to bins of media for things like setting hue and tonal range captured by the cameras to similar values between cameras. Which makes shotmatching a massive amount easier and faster.

Neil

I have one more request. I use the video limitor with the gamut warning color. It is the same color if your whites are to hot, your blacks are to crushed or you are over saturated. It would be great if you had a different warning color for each.

I know black levels do effect the saturation so maybe that is a problem, but we have a vector scope for that.