Polygon bug?

I tried creating a polygon in Color and tracking it but the result was horrible, so I set about manually moving the polygon frame by frame. After several frames, I could swear I hit the right arrow key, as before, to go to the next frame but found myself editing a clip five clips earlier!

So I clicked on the clip I had been working on, but all my work had been altered! It looks like Resolve moved areas of the polygon and rearranged all my vertices, swapping some between curves and lines! Plus there's a vertex shooting off to the upper right on a lot of these frames.

Here's a frame I readjusted after the glitch (what it looked like before the glitch)...


And here's what the frame just before looks like after the glitch...


And some frames even had vertices that shot off to the upper right...

Doesn't explain the issue, but maybe using Magic Mask would be a viable (and easier) approach?

Hi jama, do you want to Rotoscope his hand??
Why did you not use Magic Mask?
and why did you use Tracker?

It's not clear what kind of effect you want to apply to the hand, but if you're looking to adjust the grading you'll find that something simple like an oval that follows a tracker works remarkably well as long as you fuzz out the edges to obfuscate the boundary of the grade. It's pretty quick and easy to do, I'd suggest giving it a try before investing a lot of time in a frame-by-frame rotoscope.

If you really need to make a precise rotoscope of the hand, I've found that Fusion is a better tool for that job.

My first thought was to suggest another approach to isolating the hand (for an uninformed purpose since the OP did not mention what the mask would be used for). I see many have taken that route. Of course, the real question is, why did the polygon vertices get mucked-up in the first place? I don't have an answer for that. I tried to reproduce the issue with 18.1.1 Studio on my MacBook without success. I can't imagine how clicking on the right/left arrows selected different clips, either - perhaps a slip of the hand to up/down arrows?

Very strange - sorry, no explanation.

Jim Simon -
I don't have access to Magic Mask as I'm using the free version (don't have the $295 while trying to save up for a Pocket Cinema 6k - which I really wish I had for this particular shoot - which comes with paid version of Resolve).

okiewardoyo -
Yes, I'm trying to Rotoscope/mask the hand. All of the brown vegetation needs to be green, and there's enough matching brown in the skin to turn the skin green and splotchy. This is a music video that's going to have a lot of VFX and I have a total crew size of one; I'm the writer, actor, director, camera person, editor, janitor... That, and time was always against me in an ideal location that I may loose permanently in the future and Autumn came way too soon. Now I'm making summer make up shots in a Colorado winter.

I started with Tracker hoping it would be able to 'move' the mask for me but it was utterly useless; from one frame to the next, the mask would start drifting. I stayed in Tracker instead of going back to Window because you can see all the key frames as you edit (both seem to work exactly the same in this regard but give you different info). It was also easier to set your points at the beginning and end of the actor's (my) gesture and correct in between, then again between those, until all the frames were good, then you go to the next range and repeat. Tedious, but it worked great... till it glitched.

Sean Nelson -
I could have used an oval, though the way Resolve glitched on me, I wouldn't be surprised if it would have messed that up too. Anyway, using an oval (or any other shape than a polygon, including multiple ovals) wouldn't be clean enough. You can visibly see the tan background around the edges - that or green skin. Rotoscoping with a polygon is far cleaner and would provide sharper separation from the out of focus background. and I'm trying to make this as professional a video as possible in the end. (My YouTube commentaries, not so much.)

You say that Fusion is a better tool for this job. Isn't fusion using the exact same code? I would assume that a polygon, regardless of which tab you're under, is coming from the same bit of code. Otherwise, you're just creating a bloated program with unnecessary multiple sets of code to give developers more headaches (not a good coding practice). For this particular clip, I only needed to do some color grading; alter the color of the background, and then replace the sky and green T-shirt. I might do the keying in Fusion, but for this, I was just trying to get the colors right, before I go into Fusion. But you can also do keying in Color - Fusion seems to make more sense when multiple elements need to reference one same thing (similar to the coding scenario I just mentioned). In this clip, nothing references more than one element... so... Color.

If Fusion truly is better than Color, then why does Color even exist? Why does Color have Windows and Tracking, etc., just like Fusion?

Steve Alexander -
I'm with you, but changing which clip you're editing shouldn't muck-up (the polygon) in the first place. True, I was in Tracker, but I didn't hit the play buttons in Tracker after creating my polygons (you can see the one on the face that didn't get messed with, but it also wasn't the active object at the moment either). I also didn't see Tracker playing through the video either - it just plain jumped to a different clip. I think part of what I'm wondering is, is there another function, similar to playing in Tracker, that could make Resolve re-process my polygon that I don't know about yet? ...that I accidentally fired off with a fumble-finger? Or is this a bug/glitch I got hit with?

Of course, my original question was, was this a bug/glitch that happened or is there just some element to Resolve I hadn't picked up just yet.

My background -
I'm fairly new to Resolve (about 2 years of casual use), but I'm not new to video editing (used Lightworks for nearly a decade till I got fed up with all the bugs and regretted how much I spent on it). So I'm neither a newbie, nor a pro, but I do have an awesome tutor - my brother-in-law who actually taught Jon Watts (Spider-Man - Homecoming, Cop Car.) Then again, he did recommend Lightworks and my poor video quality Canon 70D!). That and I'm Autistic/ADHD so technology/creativity are my first nature.

Sean Nelson -
You say that Fusion is a better tool for this job. Isn't fusion using the exact same code? I would assume that a polygon, regardless of which tab you're under, is coming from the same bit of code. Otherwise, you're just creating a bloated program with unnecessary multiple sets of code to give developers more headaches (not a good coding practice).

The Fusion page in DaVinci Resolve is an integrated version of the stand-alone Fusion Studio product, so no, I don't believe that it's the same code. There is a lot of overlap in functionality between Fusion and the colour page, but they are really geared at different tasks. One of Resolve's strengths is that it has excellent tools to address different aspects of post-production, and if that means duplication in the code base - well, that's life I guess.

I'm a coder myself so I totally get where you're coming from with the comment about coding practice. Luckily, I'm just a Resolve user and not a developer so I don't have to worry about it.

I found this eight-minute introduction to Fusion rotoscoping that'll give you an idea of how it works:

Most of roto is not about tools but approach: how to divide focus object to shapes, where to place shape points, where to place keyframes, how to deal with changing topology etc. These topics are usually omitted from intro tutorials and most youtubers show awful to appalling roto practices. If you want to gather useful roto theory info look into stuff from either actual professional compers (who usually aren't youtubers) or from roto targeted software like official tutorials for Mocha or Sihouette.

Most of roto is not about tools but approach: how to divide focus object to shapes, where to place shape points, where to place keyframes, how to deal with changing topology etc.

My basic strategy for rotoscoping includes:

1. Use separate polygons for objects that move differently (i.e., do arms and torso as separate items).

2. Create your first keyframes (i.e., adjust polygon shapes to match the subject) at the first and last frame, and at points where the movement changes direction.

3. Go back in and add new keyframes between the first ones at the points where divergence between the polygon and the subject is at its maximum.

4. Repeat step 3 as needed.

If you have cyclic motion (a tracked shot of someone walking, for example), you can save time by modifying (2) to add your first keyframes at each repeated point in the cycle where the subject is in the most similar position. And with Fusion you can take other intermediate keyframes from one cycle and copy them to other cycles to minimize the amount of adjustment you need to do.

Another handy trick in Fusion is to use a tracker to stabilize the frame before applying the rotoscoping, and then after the rotoscoping use a Transform Node with its Center, Size and Angle attributes connected to the "Unsteady Positions" of the tracker to reintroduce the original motion back into the frame. This eliminates the need to adjust the polygons simply because the camera moved, you only have to adjust them for genuine subject movement.

These are all reasons why I think Fusion is a better rotoscoping tool than the Color page - although I confess to doing very little in the Color Page and therefore it may be able to do some things I'm simply not aware of.