That gradient from Vegas is not suitable as a calibration tool, I've already tried. The locked pixels may just be a remnant of integer math processing. 0=0, 255=255. Those of us who scan and restore old photos learned to work in [1, 254] space decades before high bit float processing became practical, for that very reason.

-- Try creating your color gradient correctly in photoshop. See if the anomaly reads differently.

-- Now try a float project. Difference?

At least same generated media works fine when using other color correcting tools. It's only Vegas' Color Curves having this issue.

Bears further testing. Curves is about the only cc tool I know that can decimate a linear math function with a transformation that creates two Y (output) values for one X (input) value, as the image shows.

Y=170=255?? It's a limitation of 8 bit integer math.

I can easily demonstrate this with a grayscale image without invoking a curves filter, and assuming my flu recovery continues, may give it a go later today.

It also occurs in grayscale images. A white dot will not darken and black will not lighten. This is good to check with the checkerboard pattern. The error thus also affects the value 0.

Yes, I learned about this in the late 1970s when our film lab got our first RGB slide scanner. It used an analog photomultiplier, three passes, and a/d conversion.

It was that way then, too, and reproducing your tests in Photoshop should give similar results. A curve (function) may have only two endpoints, or output is no longer a function of input.

Start with a real linear gradient at 0-255. Play with the curves. Toggle the secondary cc in Vegas to show you where clipping occurs. Now create another gradient at 1-254. Check for stray clipping, and play with the curves again. Light bulbs should come on almost immediately. And now you know why gamma is my go-to tool for general grading, not curves.

Set the endpoints, play with the rubber band. That covers 90% of imaging.

Keep investigating, Matthias, you are onto something that is not peculiar to Vegas, but which awareness of will make you a better imager.

Stop it.

What you are doing effectively is cutting yourself with scissors and then blaming the scissors and the manufacturer.

'Color Curves' is one of those FX that work just fine, as they are supposed to!

Go fix your brains and your hands!

_______________________________________________

Notes:

i.
...In fact, I do not like "bezier handles" philosophy much. I would prefer the same spline behavior which was in use in Photoshop's curves (and I would like to have export-import from-to Photoshop & Corel Draw). But, sigh.. It's totally operational right now.

ii.
What are the FX which "do not work just fine"? One of the examples is the 'HSL Adjust' (Hue - Saturation - Luminance). Where the 'saturation' uses an unknown to me "matrix"/idea of color /channel proportions. What do I mean by that? -- I mean, the desaturated image is wrong, it is not the pure Luma Signal (in other words, the pure black-and-white video with color data stripped off)(it's "Y" without "CbCr") it should be.
Well, Sony/Sonic Foundry were not alone here. Boris FX also exhibits this incorrect behavior. They had even implemented some "P" mode (HSP) in an attempt to get closer to the correct Luma signal representation, but this "P" is also wrong. I don't know what the problem was/is, it just takes a walk to the International Telecommunications Union's site and reading the "Recommendation BT 709" document to get your hands on the proper matrix coefficients for Full HD pure-luma signal. While "Recommendation BT 601" will provide you with matrix coefficients to SD video.

...OK, for those who has trouble reading the Recommendations, here it is:

Luminance Pure Signal of HD  (bt.709):

Luminance Pure Signal of SD  (bt.601):

iii.
Wonder, is there anybody out there, who managed to implement the correct Desaturation operation for HD video?
Yes, there is one company, one FX (actually, the sole one I'm aware of, doing it right) -- 'FilmConvert Pro'.

@Marco. Yes, that's fine. If you just want to move the start and end points horizontally, you can not do that. You have to insert a new point in each case. So I pushed the inserted point to the vertical limit left = 1 or right = 254. I assumed that it could be pushed up to the values 0 and 255 (an in PS). That was the mistake.

@Musicvid. Many Thanks. I also worked with cc in Photoshop for a while and I know the problems. But I fell for the peculiarities of Vegas.

Stop it.

What you are doing effectively is cutting yourself with scissors and then blaming the scissors and the manufacturer.

Color Curves is one of those FX that work just fine, as they are supposed to!

Go fix your brains and your hands!

That's a bit harsh @Jam_One. Nobody is blaming anything. It's healthy to question and investigate. That IS the "brain fixing". The right conclusion was reached and readers are now aware of a possible gotcha that they can avoid.