I'm about to write a plugin for Final Cut which should imitate the Photoshop RGB-Curves. But I have one problem/question which I just can't get answered even with extreme googleing:
What is the interpolation-formula Photoshops curves uses to interpolate between the points?
It seems to me that Photoshops curves inpolation is both unique out of all curves out there (Apple Color, etc.) and best regarding the photographic quality compared to the effort to tweak a curve. Other implementations of such curves-tools often use interpolation-schemes like Bezier, but they feel really inadequate for this application. So I absolutely want to implement the interpolation like Photoshops curves does, but I have absolutely no idea what the formula could look like.

Be careful, it might be patented.

The plugin is now almost done. You can download and test it here:
http://www.dominik.ws/rgbcurves.zip
I also attached a screenshot of it to this post.
The only missing thing is a good interpolation between the points. Currently linear interpolation is used. If someone of you could give me a hint what kind if interpolation I should implement, I will do it! :) Please give me some feedback what you think about the plugin!

That's a great idea. I always thought they were just B-splines. I think it would be a lot more useful if you could edit the curves directly, break them at the point so they can linear in and Bezier out.

I thought Apple started improving their graph editor, it was good for a while in variable speed, but it never really went anywhere.

Is there a high-pass filter in FCP? That's a good filter for sharpening, if your taking requests...

A suggestion: Use Color.

It already has curves and is an immensely powerful color correction tool.

I always thought they were just B-splines.
Thank you! I finally discovered that Photoshops curves uses so called "natural cubic splines". I implemented them now into my plugin. Here you can download and install the result (I used fxplug sdk 1.2.5):
http://www.dominik.ws/rgbcurves.zip
Btw., a 16bit (unsigned short) per channel lookup-table is internally generated and used, so the image processing is fast and posterizing free (but not GPU accelerated right now. If you know how to write an ARB fragment shader which uses a lookup table, please let me know!).
A sreenshot is attached to this post which shows the plugin in action.
Please give me some feedback!

Is there a high-pass filter in FCP? That's a good filter for sharpening, if your taking requests...
What kind of high-pass filter? Like the simple sharpening filter or more like unsharp mask?

A suggestion: Use Color.
I don't like the behaviour of Colors Curves. Also I don't like to even start Color up. I think the workflow is very inconvenient.

Your filter sounds good but the download installer file seems to be empty, only 16k. Could you post the filter without the installer package?

Thanks Dominik,

Plugin works great and I like it. Is there anyway to add a point to the curve rather than adding a point as it moves. I say this because as I add a point the cure moves and I may not want to add a point in that spot.

Cheers

Your filter sounds good but the download installer file seems to be empty, only 16k. Could you post the filter without the installer package?
Well, the installer isn't empty, but of course (I guess it's a trust issue) I can also give you the raw fxplug File/Folder:
http://www.dominik.ws/rgbcurves2.zip

Is there anyway to add a point to the curve rather than adding a point as it moves.
I just added this feature. With the right mouse button you can now add a point which initially doesn't alter the curve (x value comes from your mouse, y value from the current curve). I already updated the files rgbcurves.zip and rgbcurves2.zip on my server, so you can immediatelly download the new version.

Well, the installer isn't empty, but of course (I guess it's a trust issue) I can also give you the raw fxplug File/Folder:
http://www.dominik.ws/rgbcurves2.zip

It's not that, but it didn't install after running it. But thanks for the direct plug-in. I'm going to try it now.

Not to be a nuisance but the plug-in unzipped as a folder.

Not to be a nuisance but the plug-in unzipped as a folder.
Yes, you have to copy that folder to /Library/Plug-Ins/FxPlug (or ~/Library/Plug-Ins/FxPlug). But I guess the folder is already there, because you already executed the installer package. I'm not sure why my plugin isn't shown in your plugin-list. Which version of Final Cut do you have?

Hi Dominik,

Where can I find the updated cures version for downloading?

Cheers

I have been testing this Dominik, and it works great, what a great time-saver and so easy to use.
Well done and thanks.

Where can I find the updated cures version for downloading?
Same address as the older:
http://www.dominik.ws/rgbcurves.zip

@William
Try downloading and installing it again. I've changed its "group-uuid", which is responsible for identifying the different plugin-categories. The last version had a default one, which perhaps conflicted with another plugin you have installed.

Yes, you have to copy that folder to /Library/Plug-Ins/FxPlug (or ~/Library/Plug-Ins/FxPlug). But I guess the folder is already there, because you already executed the installer package. I'm not sure why my plugin isn't shown in your plugin-list. Which version of Final Cut do you have?

FCP 7 on a MacPro. However, I just downloaded the new installer on my laptop and your plug-in loaded like a charm. Works great. I'll try to reinstall it on the MacPro later. That's the machine I'll use it on.

Thank you for the hard work that went into it.

Thanks Dominik,

The plugin works great. I have been looking for a plugin like this for a long time. Thanks for the research and development on this and keep up the good work.

Cheers

Yes, you have to copy that folder to /Library/Plug-Ins/FxPlug (or ~/Library/Plug-Ins/FxPlug). But I guess the folder is already there, because you already executed the installer package. I'm not sure why my plugin isn't shown in your plugin-list. Which version of Final Cut do you have?

Hi Dominik, I'm on a MacPro as well, everything seemed to install OK but the plug-in doesn't appear in my effects palette. There is a folder installed at /Library/Plug-Ins/FxPlug/RGBCurves.fxplug.

Regarding the Hi-Pass filter, I guess I use it more like an unsharp mask, I duplicate the layer, set the Hi-Pass filter and then change the transfer mode, that way I can dial in the sharpening. That way you can get some subtle edge sharpening without adding a lot of noise. I shoot mostly with the 7D and with the still this method of sharpening works really well, I'm guessing that the video from this camera would benefit from this too.

Now I'm using the sharpening in Color which is OK, but it doesn't really compare to what I can do to a still in Photoshop using the Hi-Pass filter.

Hi Dominik, I'm on a MacPro as well, everything seemed to install OK but the plug-in doesn't appear in my effects palette. There is a folder installed at /Library/Plug-Ins/FxPlug/RGBCurves.fxplug.
Please download and try it again. I've now disabled the localization-option. I don't know if that helps, but let's do trial and error. ;) Btw. which version of Final Cut do you have?

Regarding the Hi-Pass filter, I guess I use it more like an unsharp mask, I duplicate the layer, set the Hi-Pass filter and then change the transfer mode, that way I can dial in the sharpening. That way you can get some subtle edge sharpening without adding a lot of noise. I shoot mostly with the 7D and with the still this method of sharpening works really well, I'm guessing that the video from this camera would benefit from this too.

Now I'm using the sharpening in Color which is OK, but it doesn't really compare to what I can do to a still in Photoshop using the Hi-Pass filter.
But Final Cut has an unsharp mask filter. So you need a high-pass filter?

I know this is somewhat old news, but I'd like to play with it and can't get FCP to recognize it? I"m on FCP 6, by the way.

There is indeed a library/plugins/fxplug/rgbcurves.fxplug folder, but don't see it in FCP.

Same problem here.
Can’t make it work. It installed in library/plugins/fxplug/rgbcurves.fxplug folder, but nothing shows up in Final Cut Pro.
I’m using a Mac Pro with FCP 6.

I just tried emailing him directly.

Thaks Josh.
I'll wait for feedback then.

This is a great thing to have... I usually use just the level corrections in photoshop (and after effects) so that would be really awesome to have. But having curves in FCP is great too, thanks.

Hey Aric, did you manage to get it to work?

I got it to work........I had to change the sharing and permissions in the "Get Info" box to read and write for me. Otherwise, the folder was locked.
Pete Stone

Can you elaborate? Where is this magic box?

I think I did what you said. . .(me) and "staff" have read & write permissions ("everyone only lets you select "read only" or "write only") on the RGBCurves.fxplug, plug ins, and fx plug folders. I'm still not seeing anything in FCP.

This should show up in the effects tab under video filters/neat video, right?

Can't make it work. Now if I install it doesn't create a folder anymore. Just a plugin file in the fxplug folder with the name RGBCurves.fxplug. But it doesn't show up in FCP, even if I change the sharing and permissions settings.

Ditto. Disappointed, but with tinges of hope.