Hi everybody,


I have a problem with my color grading tools on Kdenlive. I'm on ubuntu 15.10 Wily with the las stable kdenlive from sunab repository.

The problem is, if I use the color grading tools, I have an anomaly and I want to know if it's a problem with my system or not.

http://i.imgur.com/k9YSE54.png

If you look at the above picture, you can see the Cyan color on the clip monitor. The anomaly is that, the tools for color grading (the RGB parade and Vectorscope) on kdenlive indicate that the color is rather yellow :

- RGB Parade : this tool show the red and green bars at the top, and the blue bar at the bottom : red + green = yellow
- Vectorscope : the yellow arrow in the picture, that I added to it, indicate the point printed by the vectorscope. So this point is in the yellow small circle.

Instead of this, we should have the green and blue (green + blue = cyan) at the top, and the vectorscope should indicate in the Cy small circle.

By examining this problem by varying the color in all the color spectrum and observing the vectorscope. The result of this is that, the colors in the line passing trough the green and magenta are corrects, they match what I see in the monitor clip. But if I quit the Green point in the clip monitor and want to go to the yellow color, the vectorscope will show me that I am going rather to the opposite direction, meaning to the cyan.

After this, I installed the last unstable kdenlive from sunab, ... same result, even with the last version from official ubuntu repo, I have the same result.
Can some persons try to reproduce this on their computers please? I want to be sure that it is not my computer.

Is there any workaround for this problem?

Thanks!!

I concur entirely with your observations.

I'm running KDenLive 15.12.0 (from Sunab's ppa) on Kubuntu 15.10 (AMD 64)

I've just done some tests. Created a series of raw RGB24.avi clips of the pure primary/secondary colors:

Red RGB 255,0,0 Hex #FF0000
Green RGB 0,255,0 Hex #00FF00
Blue RGB 0,0,255 Hex #0000FF
Cyan RGB 0,255,255 Hex #00FFFF
Magenta RGB 255,0,255 Hex #FF00FF
Yellow RGB 255,255,0 Hex #FFFF00

Loaded them into KDenLive and pulled up the Vectorscope and RGB Parade.
In both scopes:

Red is presented as Blue:
http://i.imgur.com/WRyZewe.png

Green is presented correctly:
http://i.imgur.com/uThZAld.png

Blue is presented as Red
http://i.imgur.com/5N5oVIi.png

Cyan is presented as Yellow
http://i.imgur.com/26h6pWg.png

Magenta is presented correctly
http://i.imgur.com/lA6Tgz5.png

Yellow is presented as Cyan
http://i.imgur.com/Pxl4E3k.png

Like you say, it is as if the colors presented on the Vectorscope have been flipped on the Green-Magenta axis. Since the same pattern of misrepresented colors is also observed in the RGB parade, clearly there is a fundamental error (bug) in the derivation of the RGB channel values. And since the YUV (Y PbPr) values will be derived by Rec709 conversion from RGB, it is logical that this will be reflected in the Vectoscope.

It goes without saying that this misrepresentation renders the scopes useless and misleading.

I've only recently started using KDenLive and have yet to put a full-blown edit project on the timeline. Until now have been preoccupied with examining the behavior of different input and output video formats with respect to YUV luma scaling. I was going to start look at the "color" scopes next, so I'm very glad you have picked up on this.

I would suggest that this needs to be filed as a bug. I can't see there being any practical workaround.

Edit: Just gone on to repeat the tests in the KDenLive 0.9.10 running on Mint KDE 17.3 (AMD 64) and there all of the colors are correctly represented on the Vectorscope and RGB Parade.

Thanks for taking time and examining this problem in your system.
I will submit a bug repport

Inapickle wrote:Red is presented as Blue
Green is presented correctly
Blue is presented as Red
Cyan is presented as Yellow
Magenta is presented correctly
Yellow is presented as Cyan

Exactly the same misrepresentation of colors on the RGB Histogram also. That's with KDenLive 15.12.0 (from Sunab's ppa) on Kubuntu 15.10 (AMD 64) again.

cedricl wrote:I will submit a bug repport

I see you have:
https://bugs.kde.org/show_bug.cgi?id=359541

Inapickle wrote:Like you say, it is as if the colors presented on the Vectorscope have been flipped on the Green-Magenta axis. Since the same pattern of misrepresented colors is also observed in the RGB parade, clearly there is a fundamental error (bug) in the derivation of the RGB channel values. And since the YUV (Y PbPr) values will be derived by Rec709 conversion from RGB, it is logical that this will be reflected in the Vectoscope.

It's just struck me what's possibly happening here. If the RGB channels are somehow being read off in reverse (BGR) it would totally explain the color switch patterns observed. Green and Magenta are not changed because their R,G,B codes are symetrical (palindromic) - Green 0,255,0 and Magenta 255,0,255.

Looks like the bug has been fixed in KDenLive 16.07.70