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Histogram Bezier

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Can anyone explain to me the intended use of the Histogram Bezier plugin? I ask because to my mind it is both not working correctly and partly working in reverse. I could be wrong in my expectations of course, but I want to use it for colour correction and it doesn't work as expected.

Linear: Seems to work but the "curve" between adjustment points is straight, I would expect it to form a curve as the adjustment point is moved.

Polynominal: Extending the handles does not change the radius of the curve, even though it says it does in the manual, which makes it less than accurate and therefore not much use.

Bezier: Works completely the opposite way to any other Bezier curve I have ever seen, starting with a preset S-curve which has to be altered by the handles, rather than a neutral, straight curve which is adjusted by moving and extending the handles to produce the required curve, much like Polynominal should. Unless there is method of using it that I have not yet found, it also is not much use.

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Linear mode make nodes (control points) angular.

 

Polynominal create a node with handles but handles can only be used to change the slope (more or less) of the curve not the radius (or better you can not control the radius) of the curve. You can not to stretch the handles as you can do in Inkscape when you want to create a shape. It doesn't matter which of the two handles you are using. It is a kind of Auto Smooth.

 

About Bezier interpolation I understand you and it is not very intuitive. Unfortunately it create the S-curve also for all the 3 channel (R - G - B). In the year 2018 the developer had done a lot of work on this effect and the behaviour of the handles was not changed because it would have been incompatible with old projects, I think. However we can use this interpolation in some cases.

Usually I use Polynominal interpolation because I can control better what I want.

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Thanks Igor.

Copied and pasted from the manual: "The Polynomial and Bézier types introduce control handles that allow for more sophisticated and smoother adjustments. The quality of the result is much better, but they require more experience for their optimal use. Extending the handles away from the control point increases the radius of the curve at that point."

Which you and I both know doesn't happen, but it is confusing. What would it take to change it to a normal Bezier? It would make it more flexible and it could still be used the same way as currently. The present backwards-working Bezier could be left as it is.

What would make the Polynominal even more useful would be a grid, preferably selectable and adjustable. It would also be nice if Linear could be switched to a curve if required. Just my wish list! Now, if only I was a programmer.......................

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Extending the handles away from the control point increases the radius of the curve at that point

I think that it is right for half, and probably from a coder point of view it is correct, I don't know. As a user I agree with you. Unfortunately I am not a coder to perform such improvement.

If you have a little time, go to the link https://lists.cinelerra-cv.org/pipermail/cinelerra/2018q4/010294.html and read. It doesn't solve your request but you can understand about it.

It would also be nice if Linear could be switched to a curve if required.

What I know, you can do that. You can switch from an interpolation to another without loosing your control points (nodes). ...If I am not wrong.

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Posted by: @igorbeg

It would also be nice if Linear could be switched to a curve if required.

What I know, you can do that. You can switch from an interpolation to another without loosing your control points (nodes). ...If I am not wrong.

 

Not quite what I meant, I was trying to say if the Linear "curve" could be changed into a curve within the Linear interpolation and vice-versa. I hadn't tried changing from one to another to see if the points stay put, I'll try that as an experiment purely out of curiosity.

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I have corrected the manual. Thanks for pointing that out.
Phyllis, I am attaching the corrected file.

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Thanks @andreapaz. I am sorry, unfortunately I don't see your post in Guest mode.

@DeJay

You can switch from an interpolation to another without loosing your control points (nodes)

I tested it again on Cinelerra-GG_20201031 release and I can confirm that it works.

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Topic starter
Posted by: @igorbeg

I tested it again on Cinelerra-GG_20201031 release and I can confirm that it works.

I also tested it on the test only appimage, which I am currently using and it works for me too, however as I said in my previous post, that is not what I meant.

Andrea: Yes, that's a result and it will prevent more confusion, but a better one would be to leave the manual and make the handles work as it said they do. Well, I can dream can't I? 🙂

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