View Full Version : Remove fringing?

03-20-2010, 06:39 AM
I've got an image flattened to a 1 layer psd saved on a transparent background. I was hoping that, in LW, just inverting the alpha channel and feeding it into Transparency would give me a nice clean image. Needless to say it doesn't appear to be that straight forward as I'm getting a black fringe around my image!

Is there a trick in LW that will help me remove the fringing? I want to try and avoid saving out 2 versions of each image (1 with image, the other tweaked alpha). Perhaps saving as a psd is the problem. What file format would you use?

Thanks, Mark

03-20-2010, 10:50 AM
I think this is happening because of the half transparent pixels from the AA. You can disconnect the color input and make the color just white.

03-20-2010, 10:55 AM
Is there some kind of simple choker or minimum/maximum filter in LW? I've tried a gradient but that just tightens up the AA, I might as well use a clip-map!

The image is only white here for demo purposes. Thanks.

03-20-2010, 06:57 PM
I've read elsewhere on this or other forums that others have had problems with .psd. I mostly use .png in the manner you describe and haven't had a problem but I don't understand why .psd would be a problem..

It isn't clear to me if the shirt image is a LightWave render. If it is, the reason it looks like that is that you probably rendered with "Premultiply Alpha" ( see render globals/ Output ) on a plain background.

03-21-2010, 01:31 PM
Thanks for the responses. It's been driving me mental! I've been doing a bit of digging and it turns out, as you said, people are getting good results with pngs. I've tried nearly every format under the sun, even out of AE but I'm still getting the fringing. I've had it working once - making a separate b/w image for the Transparency channel, but even then I have to run the Minimum filter in PS by 1 to reduce the edges. Loads of effort for something quite simple!

Can anyone share their png export workflow just in case I missed something? Ta.

03-21-2010, 03:37 PM
I think I understnd now. I reread your 1st post. You said you flattened your image to one layer. I'm no expert ( I am the Dumb Bunny). But, whereas it's good to reduce to one layer, when you flatten image you lose all transparency. When you try to reintroduce transparency (eg magic eraser) your nice blurred edge stays opaque.

Work flow in PS would be: Create transparent surroundings ( should be saved as any 32bit, like png. Then create your blurred edge. Then reduce to one layer if necessary (Don't flatten image.) Then save.

In the attached, top is flattened and surrounding transparency is reestablished(what you have). Bottom is not flattened (what you want) Both images are 32 bit png placed on polys rendered against a green background.

Am I close?...that would be a first!

03-22-2010, 03:06 AM
Rabbitpenny, many thanks!! You clearly have the answer there but I think I'll be picking up your Dumb Bunny mantle from here as I'm not quite following what you're doing in PS (I've only been using it for 10yrs!). Can you break it down a little more? Big thanks again!

03-22-2010, 04:54 AM
I studied that a bit and explained what I found in this thread

03-22-2010, 05:48 AM
Thanks, very interesting. Got a good result with Red_Oddity's setup. Can't get the multiplying of layers trick to work unless I save out a separate Trans matte file.

03-22-2010, 06:18 AM
Sorry, was sleeping. I'm keeping at this because despite your confidence in me, by the end of the day, I'll be learning something very basic that I didn't know. By the way, my sample render was with "Premultiply Alpha " activated, since I wasn't doing anything else with the render. My node set up was the same as yours (except for the TWO images instead of one).

Would you be so kind as to post the shirt image that you are using for your image node (for kicks, make it .png)?

03-22-2010, 06:43 AM
Thank you for you patience! Got a feeling I'm going to be kicking myself...!

03-22-2010, 07:47 AM
I apologize for challenging your PS skills. I get the same results as you. Told you I am the source of nothing helpful

I think this halo is always present but it is more obvious because of the white shirt..I do know that a transparent poly is not truely transparent until you have shut off ALL of its light altering properties.

In your example, you can make the edge look right if you add the inverted alpha to transparency PLUS luminosity, specular, glossy, reflection, and translucency. But how that works for the rest of your render is for you to answer.

03-22-2010, 08:02 AM
Not to worry, many thanks for you efforts, it's not just me! Zardoz's post has proved to be very useful too. All good stuff to bear in mind for future development.

04-07-2010, 07:04 AM
A unpremultiplying node would be nice to have, like knoll's unmult filter for after effects.