AFAIK, this is a bug.
See http://www.sonicfoundry.com/forums/ShowMessage.asp?ForumID=4&MessageID=85442 and
http://www.sonicfoundry.com/forums/ShowMessage.asp?ForumID=4&MessageID=93525.

Best as I can tell, the bug deals with the "end-points" of the curve. As you get a
near-white original, the curve "pops you over" into a pure yellow or purple result.

If you reduce the curvature of the curve, the bug is reduced. This is one solution.
Another solution is to abandon the effect (what I wound up doing) and use the other effects to provide the same result. Not as pretty or powerful, but until the bug is fixed, it is a real PITA to have to step frame by frame to ensure the "flash" doesn't occur.

As a work around until the (bug?) is fixed I've has good success setting custom end points very close to the ends which prevents the actual ends from moving (anything below the set point you add for shadows or above the set point for highlights)

Thanks for your replies.
As I mentioned in my original posting, I am getting this annoying result even when I am using the presets (confident that SF hasn't gone over the top with the presets ...)
Therefore, I tend to agree with RichMacDonald, that it may be a bug.
Funny that SF hasn't bothered to reply to this. Wonder why ...
BillyBoy, I was pretty lost with your last recommendations about set points. Can you kindly repeat using rookie language, please ? Thanks.

Drag a file to the timeline then drag the color curvers filter to the timeline by selecting Color Curves from the list of filters. The FX filter window should open. If you can't see the whole FX window, drag what looks like double lines right below the transport bar (underneath the play, pause, other controls) up to increase the space the FX filter window gets.

You should see a little check box that shows all channels in the lower left bottom of the window once you extend the FX window to its full size which is rather large. Even at higher screen resolutions this will hide all but the top couple tracks of the timeline, If that hides too many of your tracks seperate and drag the FX window up and away from its docking position to a more appropriate screen location. You can always return it later.

By dragging the words 'color curve' to the timeline without first selecting any presets you should now see a single diagonal line running from lower left to upper right. There should be a blue box with a small white square inside at either end of the line plus two smaller black boxes along the line. Vegas Video refers to these as points.

I wish there was a grid, maybe in the next version. Just eyeballing it, visualize as close as you can the middle of the diagonal line, then right click selecting 'create point'. A new blue box with an inner white box should appear on the diagonal line along with two new smaller black boxes. You now have more control points which can ajust the "curve".

Move your cursor over the center point you just created. The cursor should change to a four headed arrow. While holding down the left mouse button over the center point drag the line. While you may move directly up, down, left or right, you should move diagonally making a smooth arc. Note how the distant points on the curve move very little while the area of the curve you are dragging moves a fairly good distance. Observe the changes in the preview window as you drag back and forthe just to get a feel how the filter works. Depending on the power of your CPU you may need to wait a second or two to see the effects in the preview window.

If you drag the center point far enough you will begin to see a line from the blue/white center point connected to either lessor black point extend outwards from their original position.

To further adjust, move your cursor over one of the lessor black points and slowly by moving your mouse over the point swing in a circular direction either clockwise or counterclockwise. A little adjustment goes a long way. Don't over do. Observe how the diagonal line changes shape as you move the set points while observing the effects in the preview window.

The shape change you are trying to get should have the original diagonal line end up looking somewhat like a flattened "S", hence the name "S" curve. Hint: Don't try to get something that really looks like a traditional S, that would be way too much of an adjustment. There is hardly any curve in the middle and a pronounced flattening at the ends. Calling it a "S" curve isn't very accurate, but I guess they got to call it something.

Now that you've made a simple "S" curve you can get more control by adding additionl points. Try adding additional points by clicking roughly 1/4 of the way down to the left lower corner and another the same distance from the upper right area. Applying what you learned, further refine the curve.

Of course every source file will respond differently. What you probably want to do is first SLIGHTLY move the center point upwards and to the left if you need to lighter the video and SLIGHTLY downwards and to the right if you need to darken the video. This preliminary adjustment effects midtones most, however as you observe, you'll notice both the shadow areas (lower left bottom of curve) and highlights (right top)also will move a fair amount.

Since it is rare for any video to need the same amount of adjustment in all three areas, midtones, shadows and hightlights, by adjusting one section at a time the other areas are not effected.

To see the result of effecting just shadows, put a new point halfway between the original bottom black point and the next up black point. It should be roughly 1/4 of the way up the line where you want to set a shadow point. Now adjust this new point as you did the others. Repeat adding another set point 1/4 from the upper right top to adjust highlights.

Notice that the area between the center blue point and either the top or bottom blue point depending on which you are adjusting effects only that half the curve with the remainng half is "locked" in place.

Doing these steps along with making some minor changes with the levels filter can work some real "magic" on otherwise less then good videos. It just takes a little practice learning what does what. Once you're happy with the custom filter you made you can name it and it will be added to the preset list for use another time.

You can also use any of the presets as a starting point and modify them. Being a "knob twister" I like the extra control you get starting from scratch. :-)

I used the FX a lot this weekend and noticed some more things:

1) I do *not* have a problem with any of the presets.

2) If I take a preset and tweak it a bit until I get the problem, then "undo" the changes by making that line as straight/diagonal as I can, I *still* have the problem, i.e., once I have a problem I may not be able to undo it no matter what I try.

3) The problem is not limited to overly-strong modifications to the bright endpoint of the curve. It can occur simply by adding a new point to the middle of an existing "zero-modification" curve.

Darn that floating point math :-/

Sure hope we get this fixed soon. It is *the* tool. I took an overcast, grey-sky, very dull shot of a bald-eagle circling, and I was able to show the whites of its tail, the yellow of its claws, and the shadows and variations of its different feathers. A crappy scene became wonderful.

can somebody dial in the bad behavior, save the project and email the project file?

thanks-

drdropout@sonicfoundry.com

BillyBoy, you're tops !!! Thanks for the full, competent explanation ...
SonicEPM, I will try to reproduce the bug again (as you may understand, these are not things to keep...)

>SonicEPM, I will try to reproduce the bug again (as you may understand, these are >not things to keep...)

I sent in an example last night. Hopefully, SonicEPM is able to reproduce it. If not, he can post here for us to give it another try.

Thanks to Rich M for helping us track this down. There are apparently some funky points in the color curve filter, and these may appear between "good" keyframes if you are using more than one (non-hold) keyframe. (As we ramp through the curve during interpolation you may hit a bad spot).

It'll take awhile to fix this (don't count on it in the very next update), so if you are using color curves:

1) Set preview quality to "best" and "display at project size" to make sure you don't land on one of the buggy curve points. If you see the strange pixelly colors, make a tiny change and it should go away.

2) Avoid keyframing color curves if you can. A single keyframe will not change over time, and the setting is either bad or it isn't.

Thanks to everyone for helping us repro this bug. You can still use the color curves right now- just be aware of #1 and #2.