Scrubbing a clip reveals a different contrast

[Phil Gosselin]

Hi all,

Please take a look at the screenshots attached. The "No scrub" is for when I am doing nothing, notice the waveform.

The "Scrub" is when I am scrubbing (shortening) the clip, now see the waveform and the contrast in the shot!

I had all those clips color graded, because of a LONG story my grader rendered everything in QT Animation. Back to my place I imported all clips and now I have to redo the slowmotion. I do mine by frameserving in VirtualDub through an AVS script.

When I do that I reencode in a lossless format, Huffyuv and reimport in Vegas.

So the clip I am scrubbing in the screenshot has gone through this process. I have tried with another lossless codec, Lagarith, which yielded the same results.

Two things
-If I scrub the original QT Animation It also reveals a different contrast, one which has super blacks
-If I were to redo the slomo process the resulted clip would lose another 10-15% contrast. Scrubbing through it would reveal the "second" original contrast level.

Why is this happening?

Thanks

[Seth Bloombaum]

I don't have a direct answer for your question, but in this situation I would try some sample renders to whatever your destination format will be. Do these setup and gamma variations show in renders in any way?

This would, in turn, help me to understand how seriously this might impact my product, and how much time to spend on further analysis.

It sure looks like some 0-254 vs. 16-236 B.S.

[Phil Gosselin]

Well kinda of an update.

It occurred to me that the "scrubbing" effect is the same as when there are effects applied in a clip. When I scrubbed an FX'd clip the preview window will show the original video.

So now my cursor is on a clip and when I press the "split screen view", set to FX Bypassed, I see this gain in contrast, just like the scrubbing effect described earlier. Before I activate this function my black show to be on 16 and when I deactivate it they are at 0

Now I do not have any FX on that clip so what could explain this behavior?

Thanks

[Adam Stanislav]

Originally Posted by Phil Gosselin

Why is this happening?

Because you scrubbed it? I cannot test it because Vegas locks up when I try, but presumably, scrubbing works by combining data from several frames. Essentially it is resampling the images, but in the temporal manner rather than spatial (as in usual resampling). And resampling can change the contrast of an image. So it is not really that surprising.

[Phil Gosselin]

Just want to make sure I used the proper word here. By scrubbing I meant to put the cursor on the edge of an event, click it and shortened it. Does your explanation still stands with this definition?

Actually let's forget about "scrubbing" for a minute. This morning I dropped one the original clip, an MOV from the camera, and simply activated the "Split Screen View" (set to FX bypass) and there it was, a shift in contrast. It as is there is an FX on the event when there isn't

What do you think?

Thanks

[Adam Stanislav]

Originally Posted by Phil Gosselin

JBy scrubbing I meant to put the cursor on the edge of an event, click it and shortened it.

I guess I misunderstood you, then. I thought you shortened it in the sense you made the whole thing run faster. If all you did was change the starting or ending point of the clip (or both), that should not affect the contrast.

[Nicholas de Kock]

Usually when you "scrub" all effects are turned off automatically however as you have no effects on maybe Vegas decreases the quality of the clip while you are scrubing to increase performance? Either way it shouldnt affect the final render.

[Edward Troxel]

When I "scrubbed", it showed me the actual frame I was on during scrubbing so the scopes were moving all over the place. When I stopped, it then went back to the frame the cursor was on.

[Phil Gosselin]

Well it does affect the contrast....

Anyhow, I did additional test, this time I wanted to see if it had something to do with the project it self.

Sure enough if I select everything and copy/paste into another instance of Vegas all the clips look fine. If I shortened the contrast stays the same and there is no degradation in contrast if I render into a lossless codec and reimport the clip onto the timeline.

So I guess this my project was somehow "corrupted" and if all I have to do is copy the whole thing into another instance I will

When I do that though no keyframes are copied into the other instance of Vegas. All clips and tracks are there but all the keyframes that I used in motion tracking don't get copied.

Is there anyway to copy them or will I have to redo them all manually?

[Edward Troxel]

Can you manually select the keyframes in the Track Motion screen, copy them, and then paste them in the Track Motion screen in the other instance of Vegas?