Yikes, I appear to have filed the same bug report in triplicate:

https://bugs.kde.org/show_bug.cgi?id=361163
https://bugs.kde.org/show_bug.cgi?id=361164
https://bugs.kde.org/show_bug.cgi?id=361165

First time I tried to post the report, there was some server error message, so I tried again...and then again...but it appears all three went through.

How does one delete a duplicate report ??

TheDiveO wrote:I vaguely remember seeing similar bleeds when playing around with cairoblend bit thought it was my mistake

Well I can't see any of this type of chroma aberration when applied as Normal (Cairo) blend between dissimilar clips:
E.g. Normal blend 50% opacity
http://i.imgur.com/momRXg3.png

But it's definitely there again with Overlay, Hardlight, Softlight, Screen, Color Dodge and Add.
E.g. Hardlight 50% opacity:
http://i.imgur.com/5Eceel1.jpg

Inapickle wrote:Yikes, I appear to have filed the same bug report in triplicate:

https://bugs.kde.org/show_bug.cgi?id=361163
https://bugs.kde.org/show_bug.cgi?id=361164
https://bugs.kde.org/show_bug.cgi?id=361165

First time I tried to post the report, there was some server error message, so I tried again...and then again...but it appears all three went through.

How does one delete a duplicate report ??

Deleting is not possible, as far as I know; yet you can add a comment indicating these are unwanted duplicates and then set them to states RESOLVED as INVALID.

OK, thanks, done that. The valid bug report is :

https://bugs.kde.org/show_bug.cgi?id=361163

I've just been "revisiting" KDenLive and testing the last version update 16.08.3 running on Kubuntu 16.04 (AMD-64) I'm pleased to see that the (Cairo) blend mode 'opacity' bug has now been fixed. Thanks JBM.

With that I've run a few tests with some sample 1080/30p HD-AVC.mp4 clips off my Canon HF-G30 camcorder (@TheDiveO - if you are looking in, yes, I finally got around to upgrading from my HF-G10. Really like the HF-G30). In addition to what I'll call 'Normal' recording mode, the camcorder offers a 'Cinema Mode' that has various (rather dated) 'film-look' presets. But it also has a 'Standard' cinema profile, with some adjustable settings for Contrast, Brightness (Key), Colour Depth (Saturation) and 'Softening' (softening only, can't increase sharpness). My interest in the 'Standard' profile is it has a flatter (lower contrast) 'gamma' curve, with a slight black-lift and smoother highlight roll-off, that lends itself as 'canvas' for creating other (higher contrast) filmic grades in post.

Here's one example of how a 'Softlight' self-blend (using the same clip for the top and bottom layers) in KDenLive can be used to produce a nice 'filmic' tone effect:

http://imgur.com/a/jlKLs

These are frame grabs taken from a DNxHD render of some sample HF-G30 clips processed in KDenLive. The first image was from a clip shot recorded in Normal mode (ProgramAE with +12db AGC limit). The second shot in Cinema Mode with the default profile settings (Mid-Key). No 'effects' were applied, so they just serve as reference in this example. The third image was the Cinema Mode clip again, but in this case I increased the Gain (using Lift/Gamma/Gain) to 1.3 and then applied a custom RGB 'Curves' preset that I had created a while back to emulate the look of Fuji Provia (Reversal) film stock ("Provia-esque") - Provia film has a relatively 'Neutral' tone. In the 4th and 5th images, I likewise increased the gain before applying a Softlight blend at 64% and 50% opacity. For my taste, I would probably add a little sharpening to the "Provia-esque" and Softlight blends, but I just wanted to illustrate the 'neat' effect.

The reason I chose Softlight at 64% opacity there is that prior to I had been experimenting with film emulation LUT's in DaVinci Resolve (12.5) and I found that a Softlight blend (in Resolve) at 0.638 opacity came pretty close to replicating the tonal curve of a Provia 400F emulation LUT, as shown here using a greyscale ramp to visualize the curve on the WFM:

http://imgur.com/NkgPwPt

Since KDenLive does not yet have facility to import 3d LUT's (there is a '3d LUT' entry listed under 'Misc' effects, but is not implemented yet), I wondered how the Softlight blend might look when applied in KDenLive. Not bad actually and I'd suggest that it's a rather convenient way of producing a 'generic' filmic-look contrast curve.

For added interest here are the KDenLive WFM and Parade plots for the custom 'Provia-esque' RGB curves and Softlight blend (64% opacity) when applied to a greyscale ramp.

http://imgur.com/4ZMNcY1

Note that the 'Provia-esque' curves don't quite get that 'filmic' tone curve, and the skin tones are a tad patchy (difficult to get skin tones just right with RGB curves), but it's still quite a pleasing 'look'.

BTW - If anyone is interested, the 'Provia-esque' curve was itself derived from one of a set of film look curves created for Photoshop (acv format) and then adapted for Gimp.

http://www.prime-junta.net/pont/How_to/ ... films.html

Since KDenLive can't import PS acv or Gimp curves, I 'drew' the 'Provia-esque' curves again with the 'Curves' effect. At first they were a little too 'cool' in the upper-mids so I tweaked them some to get a better result. In the above example, that's probably why those skin tone areas with a faint yellow hue are a little more patchy in the 'Provia-esque' image - the Canon HF-G30 camcorder balances skin tones a tad warmer than the HF-G10 model I used in those earlier tests.

I found a way to use blend modes with opacity control.. I am using kdenlive 21.04.1.

Here's the solution:
--Go to the compositions tab (if you can't find it, go to view and make sure "compositions" is checked).
--Search for 'Composite and transform'
--drag and drop into your clip
-- Click to select the composition and look at 'effect/ compositions stack' (if you can't find it, go to view and make sure "effect/ compositions stack" is checked)
-- in effect/ compositions stack you'll find 'compositing', this has all the blend modes and above you will find opacity control.
-- adjust the opacity to your need