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fellah
09-01-2002, 11:10 AM
when I render an image to a 32bit tga and try to compose it with other images in PS i get a small dark line around the obj..
I think it's the alpha that is messed up because I use AA.. anyone know how to fix this?

take care
// fellah

yog
09-01-2002, 12:56 PM
Sounds like you are using plain black for the rendered background, and a different background when compositing.

Try using your comosition background image (or a close aproximation of) as the render background.

RobinOberg
09-01-2002, 01:05 PM
Originally posted by yog
Sounds like you are using plain black for the rendered background, and a different background when compositing.

Try using your comosition background image (or a close aproximation of) as the render background.

hey, thats smart. :)
ive had this problem once or twice, even gave up on AA in order to composite better.
Thanks for the advice (although it was for someone else) :)

fellah
09-01-2002, 01:17 PM
yog,
that won't work as I have to compose it to a background with different colors. the idea you had will only change the color of the black line to something else if I understand right,
look here, the character is one layer and the vehicle another:

Maxx
09-01-2002, 03:21 PM
This is one that's so simple it's possible to miss, but what about the defringing options in PhotoShop? Layer-Matting-Defringe gives pretty consistently good results, although the Remove Black Matte would prolly do just as well for you.

Eugeny
09-01-2002, 06:31 PM
U can use After FX to compose...
Here's the same image using straight alpha (like in Photoshop) and premultiplied alpha. (Make zoom to see the difference)

fellah
09-01-2002, 07:36 PM
Maxx,
hey thanks, it works pretty well. not as I wanted but it's better then before.

Eugeny,
that looks good, it's sad PS don't have a function like that.. I don't have AFX so I won't be able to try but maybe it solved the problems to some other ppl, thanks for your effort!

hope newtek adds something to fix this in the future.. :wip:

yon dabuda
09-01-2002, 07:41 PM
try using a medium shade background *gray* when you render :)

and maybe green or blue.

yog
09-01-2002, 07:45 PM
Hi Fellah.
Say you have a background image and 3 levels of LW objects on top of them, the pilot being the top element. First render the lowest background object (bean holder) with the initial background image, compose in photoshop. Then render the second object (toilet bowl) with the composited background image from the first render, then add this render to the photoshop composite. Then render the top object (pilot) with the composite from the previous render as the background image.

It might sound a long and tedious job, but it's very quick and easy.
Have both Lightwave and Photoshop open at the same time. When the first composite is done in PS, go to the Image Editor in LW select the background image, hit replace and pick the composted image.
If you keep the same image name in PS and just add layers, when you next go to the image editor, and it replace it will default to the last PS image you chose so you can just hit enter.
One thing to remember, press save after each composite in Photoshop, or else when you use the replace function in LW it wont see any of your changes.

BTW
Excellent challange project you have there Fellah, can't wait to see it finished.:thumbsup:

Tudor
09-01-2002, 08:09 PM
why not just check the 'fader alpha mode' in the rendering panel?
It does just that.. premultiplied alpha.

E_Moelzer
09-01-2002, 09:05 PM
Hello
This is why there is additive compositing around these days...
I know Digital Fusion can do it and LW itself also.
Try to do the same you did with PS with LW and you will se that it works perfectly well, without the balck line around your object.
Hope that helps.
CU
Elmar

Eugeny
09-01-2002, 09:46 PM
Originally posted by Tudor
why not just check the 'fader alpha mode' in the rendering panel?
It does just that.. premultiplied alpha.
Unfortunately no...
Fader alpha mode make your images black and white with the same alpha :(
fellah - use the SpriteEdger (Scene/Image Process/Add Image Filter/SpriteEdger) - this do exactly whet u looking for - just turn ON Fix Background Fringe and choose color. I tried with black background - work weary good.
Hope u work with LW7.5 :)

Eugeny
09-01-2002, 09:50 PM
Opps, sorry the Fader alpha mode don't make images black and white (just checked with another scene) - but still alpha appear the same...


So SpriteEdger is the tool for u.

fellah
09-01-2002, 11:28 PM
yon dabuda,
yes it will make it a bit better but it won't give the perfection I'm after though, thanks :)

yog,
thanks alot for that indepth description. I will give it a try if Eugeny's way don't work(as it seams a bit faster), glad you like my challenge entry to :)

Tudor,
thanks, don't work the way I wanted to though..

E_Moelzer,
yea but I won't have the tools\interactivity in lw as I have in PS for the stuff I wan't to do, thanks though!

Eugeny,
hey thanks once again! I'll try it out asap(and get back here if it don't work ;) )

NanoGator
09-01-2002, 11:29 PM
Typically what I do is I render the object with a black background, then render out a seperate image as the alpha. Then, in AE or Photoshop, I do the following:

-Layer the alpha image on top of the background image.

-Invert Alpha so that the object is black and 'transparent' is white.

-Set the transparency mode of Alpha to 'Multiply'. What you'll see then is the background with a black 'cookiecutter' image bitten out of it.

-Layer the foreground object on top of alpha

-Set the transparency mode of Foreground to 'Screen'. This will add Foreground to Background the same way lining up two projectors on a wall will add two images together on the screen. (I think thats' where the name came from.)

Since the object has been cookiecutted out of background, then you're adding the foreground image to nothing, making it appear solid and not translucent.

This should take care of the background artifacts (only if the background is truely black...) and it also allows you to composite glows, lens flares, and other effects that aren't part of the alpha channel.

Don't know if this helps your particular problem, but I would encourage anybody interested in compositing images to look into that technique. It's really changed my workflow. =)

fellah
09-01-2002, 11:36 PM
NanoGator,
hey there, sounds like a really good trick to know, thanks for sharing your knowledge! I will try it tomorrow(a bit late here now)

take care
// fellah

Tudor
09-02-2002, 11:58 AM
Thats weird, as I used it for a project (200+ characters).. worked like a charm.
You have to save the alpha out as a separate object though I think. F9 is not an option.

Originally posted by Eugeny
Opps, sorry the Fader alpha mode don't make images black and white (just checked with another scene) - but still alpha appear the same...


So SpriteEdger is the tool for u.

a2reason
09-02-2002, 03:26 PM
Fader alpha is the correct way to do perfect composites. Tudor already said this, but I will try to explain why.

When 'fader alpha mode' from render options is active, the places where the alpha channel value is something else than white get modified in the rgb values so that when they are faded with the alpha they get the correct value.
So it doesn't change the alpha in any way, it changes the actual image data.
Normally it causes objects against background to have a crisp, aliased edge that gets smoothed when faded with alpha.

Fader alpha works only on images saved through image saver, not through image viewer.

You don't need afx to use it correctly: In photshop, if you ctrl-click the alpha channel you get a selection that you can use to clip the image to get perfect edges against any background.

RobinOberg
09-02-2002, 08:31 PM
cans omeone post and image where i find this fader alpha checkbox? i cant find it anywhere :(

Eugeny
09-02-2002, 08:46 PM
Render options/Output Files
U need to define some saving RGB or Alpha to get this option worked...

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