Texture dark edge problem

[valerie-1]

I am hoping someone might be able to give me some suggestions.

The file texture I'm trying to work with has wide soft edges like a cloud, the image is flattened on a black background and saved as a tiff with an alpha channel. If I attach this file texture to a shader in Maya it renders with a dark edge.

At work I am able to fix this problem by unpremultiplying the file texture with an in house tool which eliminates the dark edge problem in the shader.

At home I don't have that tool option. Is there a way to build a Maya shader to unpremultiply the file texture or is there another technique to create a shader that would not have this problem. Thanks for any help.

[joojaa]

sure... but you could do this in photoshop much easier.

[valerie-1]

Thank you for responding. The following is how I currently create textures with alpha channels in Photoshop.

I create soft edge brush strokes on a layer in Photoshop, (a layer above the background layer).
I load the transparency channel for that layer and make an alpha channel with it.
I fill the bottom background layer with black.
I flatten the layers and save the file as a .tiff.

I would be happy to solve this in Photoshop if I can. Can you please advise me what I need to change to save the image unpremultiplied? (is that what you meant)?

[joojaa]

now your problem is the act of flattening the image. Dont just delete that layer you use as a guide only.

But photososp tif will still flatten the image. So if you dont want taht to happen then you need to work a abit differently. you need to weork alpha fist and then paint well over it. THis prettymuch excludes normal photoshop operations tough. Fortunately for you mayta can read photoshop files in then new 6.5 so your problem is gone.

[valerie-1]

Thanks again for getting back to me so quickly.

Are you saying not to flatten the image when I save the file in Photoshop for a Maya shader?

I thought the file texture needed to be no more than one rgb layer and one alpha channel to be read by Maya's texture node? Is that still true or am I misunderstanding something about how to create file textures for Maya's shaders?

[joojaa]

OK this might be a bit hard to explain so i made a photoshop action that does this on a image with multiple layers and NO background! Note the act of unpremultiplying does make the channls look UGLY, but dont worry once you take the alpha and multiply with it you end up with the normal image. (presumably its one of the reasons people use prmulted images in first place).

You may wish to save the original PSD, and in fact id encourage to use the maya 6.5 psd file reader.

PS. it doe snot accomodate for bad alpha aliasing that could have been cause dby either bad masking or something like that.

JooDemo.atn, photoshsp CS action (~4Kb)

Save as tif with the alpha channel

[valerie-1]

Hi, just reread your previous response and some how I did not see the paragraph below which talks about painting the rgb layer out beyond the alpha channel and that after doing that we still save the file flattened.

Yes this makes sense to me and have used this technique in the past when I did not have access to a tool which can unpremultiply a flattened image with an alpha channel.

Its great news to hear that Maya 6.5 as a solution for this. I look forward to that feature when I am able to upgrade to that version.

Thank you so much for your feedback. It helps me confirm that I'm not overlooking something in Maya or Photoshop that would solve this.

I am still however, interested in seeing if there is a shader setup that would unpremultiply the file texture. I have experimented unsuccessfully with the multiply/divide node.

Do you have anysuggestions to try in Maya's shader setup to overcome this? Thank you so much for your time.

[joojaa]

you didnt because by the time you posted i was rewriting the post! Use the action its lighter on your network.

I could posta anetwork for this but its actualy quite complex. It involves mutiplying the inverse or the mask with your bottom channel and then screening the image over this.

And screening looks like this: basicaly the difference is that you pipe the alpha to the inverse instead if i remeber correctly old image.

[valerie-1]

Thank you so much for these suggestions. I'm attempting to recreate the shader setup you showed. It looks very interesting. Is it possible to post that shader node setup as well? I don

[joojaa]

sorry ive only got cs at hand! BUt basicaly what you do is

(your awfully close tough! but the copy operator is quicker and more accuarate)

merge visible layers so you only have one. (DONT flatten) Also retain tthe transparency so dont have any background chgannels delete them befroe this tep

use image calculations to extract the red channel 2 times in normal mode then you extract the blu then freen.

load the only layers alpha nd save it

copy the calculated layers contents to repective channels delete the extra ones.

and save out

Ps. dont worry not everyone has a forukm addiction