Keying : Get Rid Of This Grey Line

[user_deleted]

Hi

i think this question concerns more experienced compositors than the logical of shake's node workflow...

i am keying 2K 35mm film transfer with a lot of grain... what i did is i use a primatte to get a hard matte, then dilate/erode it to pipe it in the garbage/hold out of a keylight.. than in my keylight, i did a key with a really soft edge, keeping all my motion blur pretty well

now ive piped this alpha in a switchmatte, connected with my source footage despilled with a hue curve, where i pulled down the "green hue " above the green on the hue line down there....

when i comp a background, i loose all my motion blur blending where the matte is soft, and instead a get this grey stroke, probably comming from my despill....

wht ca i do to solve this weird artifact ? (btw, i have no premultiplication problem.. there is no CC node between the switchmatte and the over of the background

Thanks

[user_deleted]

Make sure you have connected your BG image to the background input of the Keylight function as well, not just the Over node. I had a similar problem once, only not with motion blur but with shifting transparency. Although being a great (if not the best) keyer, Keylight sometimes renders weird results if no BG image is supplied.

[user_deleted]

sounds like a good idea, but what if i want to dilate/erode or soften nore my edge with a samll blur?

and if i comp directly in the keylight, i cannot use my despill greenscreen version....

i want to solve this problem while keeping my switchmatte pipeline...

[user_deleted]

There's a few things you could try. First of all, your green suppression seems to be desaturating too much those motion-blurred edges, making them look grey. You should try color correcting those edges to match the required tone (half-way between the fg and the bg). Another thing you could do is some lightwrap effect on your FG element (basically adding some heavily-blurred version of the BG through an edgematte).
And last but not least, try comping it all using an addmix instead of an over, and play with the handles to push your motionblurred edges to the desired level.

Hope that helps.

[user_deleted]

Thanks! these are good ideas!

But i had to solve it myself, because delivery date was 2 days ago...

but for sure , next time i willgive it a try

for the light warp on the edge portion, ive tried it, and it was only adding light and making the edge brighter, wich is the opposite of what i wanted to do....

but here is how i managed to acheive something lokking good:

i did is a diffrent key, with a hard edge, excluding the motion blur... then, i piped in an XoR two version of this alpha : one slightly blur and another eroded and blures... so i got an edge matte, wich i blurred and tweaked to get it as thick as the motion blur area, and with a smooth softness, but starting inside the character and finishing on the solid edge....

then i pipe this alpha in a swichmatte,using as source the greenscreen version with the despill from the huecurve, and comp this over the same greenscreen despilled footage.... placing a move2D between the swichmatte and the over node, i offset the "edge patch" to hide the motion blur area, and did a bit of roto to delimit this "patch" and then i use this new patche plate as my source footage in the switchmatte... so i kept my softness with to good looking color that was supposed to be there......

Then yesterday, i've talked to the effect supervisor for 300 at my job, and he gave my extra tips that i think might be good to share....

he told me that i could have played a little bit more with the green hue curve inside the hue curve node that i used, to match the luminance of this area with my comp .

second, he told me that a hard edge key comp on top of this same key, but blurred a lot could do the job......

and last, as HueSatVal suggested me, to comp a version inside the keylight node, connecting the background would help to blend the edges, and then combining this key with other despill versions, with hard edges on top.... or simply to start where i was at the begining of this post, with something soft and then pipe a primatte after my swichmatte and key the grey line, to get controll and mor transparency on it

Thanks guy for sharing with me, and hope this thread will help others with the same problem

[user_deleted]

okay the best way i have found to do is a key is to pull a hard matte using primatte. erode it down away from the edge. then off the same filein pull a matte using keylight. doesn't have to be perfect white and black. use an over to put the two mattes together. copy the keylight node and in the foreground plug in your gs plate. in the bg plug in your bg plate. in the first matte field (sorry can't remember the name) plug in your over'd matte. in the second matte field take the same over'd matte and invert it. do all of your blurs before plugging in to the keylight. do all this in linear space. i always get better results pulling a key in linear space.
generally this method will not give you a line around your gs elements. also you can use the keylight where you are doing your "comp" to do any spill suppression. i do the spill suppression with the fine tunning in keylight.
using switchmattes and overs with a key always gave me some lines around my characters. and then using blurs to hide these lines degrades your edges which i guess can be passable till you start to get fine lines like hair.
most of my comps with one foreground, one background can be done with a total of 12 nodes

[user_deleted]

Is there a big difference between pulling two mattes -- hard/soft - and combining them and switchmatting, vs pull two mattes and then comping each individually and then adding the two resulting comps together -- Steve Wright describes both methods in his book and I just wondered if anyone has tried both ways in the same script to see what the difference looks like? in my mind they'd look exactly the same?

j