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What creates alpha when applying file textures , color or alpha channel?

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TomKarl
What creates alpha when applying file textures , color or alpha channel?
on Oct 31, 2006 at 6:42:02 pm

I'm following Learning Maya 7 tutorial(Using Maya 8 x64) where a file texture is projected on the object as part of a layered texture. File color out is connected to the projection, the projection is connected to a layer texture color and alpha,blend mode is over. The alpha SEEMS to work in the tutorial.

When I replicate the proccess in my project, the black and blue immage colors are transparent; the file type is TIFF with alpha channel. Adding black to the tutorial immage also creates transparency; alpha channel is not altered.

Very confusing, (Maya sanctioned) tutorial implies that alpha channel creates transparency, not image color.

Nobody responded to my earlier post. Hope this is more clear or am I missing something obvious?

Thanks


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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 1, 2006 at 6:16:49 am

Sorry we didn't reply to your earlier post--sometimes they just slip through the cracks.

Projection nodes should have outColor and outAlpha attributes. It may be that the outColor of the node is connected to the colour attribute of the texture layer while the outAlpha is connected to the mask of that layer.

Note that all File texture nodes have an attribute called 'Alpha is Luminance' which, when checked, causes Maya to calculate an alpha channel based on the overall brightness of the colour channels of an image, rather than its 'real' alpha channel (if it even has one).

Is the file texture you're using one you created, or was it provided as part of the tutorial?

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 2, 2006 at 5:10:25 pm

Hi, I know there are lots posts every day.

This occured in the sample finished file from the tutorial CD when I added black to it. Also put my image into the unchanged tutorial and it produced the same result.

I've check the alpha is luminace several times. The projections nodes' connection in the graph editor is .alpha out to .inputs[0].alpha.

This problem has not been seen before?

I appeciate your input.


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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 7, 2006 at 7:00:06 pm

Would it be possible for you to upload your scene somewhere and post a link to it? I'm afraid it's difficult to troubleshoot without being able to examine the shading network directly.

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 9, 2006 at 6:47:22 pm

I've uploaded the final example file from the tutorial. Look at the blin2 shader which has a layered texture. Switch out the bandage.tif with bandage2.tiff .

I added black and other colors to show that black is transparent and alpha is ignored. Is the tutorial grossly missleading? It says to connect the projection out alpha with input[0].alpha to create a "lable" placement. Tutorial is form Learning Maya 7: Special Effects.

The workaround of creating a separate alpha image creates extra work, is hard to sync and seems archaic. In Max this is a no brainer.

I appreciate your help.
link to file http://www.tomcuster.com/project1.zip ( don't look at my web site it hasn't been updated in 3 years)


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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 10, 2006 at 2:27:43 am

I can't open the file--corrupt? :(

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 15, 2006 at 5:08:59 pm

Sorry about that. Something messed up in the zip.
Uploaded a new one and did a down load test.

I appreciate your patience.



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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 15, 2006 at 5:24:55 pm

Okay, the scene downloads just fine, but there are no texture files included.

One more try? :)

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 16, 2006 at 6:01:14 pm

Damn, guess I got carried away striping out extra files from the tutorial project.
I don't have those files at my work computer but the shading network is exactly how it's presented in the tutorial sans file texture.
I've uploaded images I inserted into the tutoral file texture that show the problem ; see nose area with projection icon. http://www.tomcuster.com/sourceimages.zip (tested the download ;)

I know "label" file textures can be positioned through 2d attributes but it's VERY tedious to get it right. The projection can work by creating separate alpha map. This seems like unnessary work and has alignment issues. And the Official Maya 7 FX Handbook says the example shading network should work! (this is a no brainer in Max)

I really appreciate you following through on this.


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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 19, 2006 at 6:40:00 pm

Hi, Tom.

I've had some time to fiddle with your scene, and honestly, I'm as perplexed as you are.

The problem seems to be that projection nodes does NOT have any attribute for an incoming Alpha connection. It accepts R G and B colour channels, and that's all. In the absence of separate alpha information, it seems to me that the Projection node ALWAYS functions as if 'Alpha is Luminance' were checked, making its outAlpha output virtually useless--or at best very limited.

There are plenty of possible workarounds. One would involve using another projection node to carry the alpha from the file texture--plugging it through a single colour channel of the projection node. (If you connect this second projection node to the same 3D texture placement node, that should eliminate alignment problems.)

But of course you shouldn't HAVE to find a workaround for this; it should be, as you say, a no-brainer. By the way, I'm on Maya 7, so it seems the problem persists across at least these two versions.

Specifically what tutorial are you using here? What book, chapter, page, etc.? I can't recall if you specified.

Sorry for the long delays and lack of a definitive response!

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 20, 2006 at 10:45:33 pm


The tutorial is from Learning Maya 7 Special Effects Handbook, Project 1, Lesson 2 ; 02-layeredTextureDiva.ma.

It is curious that no one, including you, have stumbled over this. Guess layering file textures is not used like this very often. Even more curious is that the tutorial presents it as how to place an "lable" file texture.

I did intially finish the project by hacking through the work around. It works well for plannar placement but I need to do a Cylinder projection. The two projection maps will not move together when I do a horizontal scale - but they do for a vertical scale !??! Tried selecting both projection icons but it will only move one. Rebuilt the shading network but it still does it. I ended up scaling it with the general scale and move tools. Was able to get it to fit but was not as accurate and took more time.

My projects use a lot of "lables" in Spanish and English. If I could use the expected approach it would save me time and file size in final assets.

I really appreciate you getting down to the nitty gritty details on this.


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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 21, 2006 at 5:47:18 am

[TomKarl] "I really appreciate you getting down to the nitty gritty details on this."

No problem, that's what we're here for. That said, this looks like an Alias--er, Autodesk--thing. Have you tried taking it up with their support team?

I have the textbook you describe, but I don't have my copy at home with me... I'll have to take a look at that tutorial later in the week after I get ahold of it again.

As for the alignment problems you describe with multiple texture placement nodes... you *should* be able to simplify the workaround by using just ONE placement node in total. View both nodes in the Hypershade, then delete one, and connect the outputs of the remaining one into the inputs of the second (now placement-less) projection node. When done that way, the two textures will be projected absolutely identically no matter what.

Still more of a workaround than you should need to do.

As to why nobody else has stumbled across this issue... it does seem odd, doesn't it? I feel a little guilty, like maybe I should be using projected file textures more. ;) Seriously... I think many users layer their textures externally (in Photoshop or similar apps) and just project them simply in Maya without using a Layered Texture node. Frankly I've always been a bit fuzzy on both Layered Textures and the Stencil image mapping method... I don't know how much play they get for most users. Hopefully if someone else has helpful tips they'll jump in.

Are your labels oddly shaped? If you're just cutting out a rectangle, there's no need for alpha masking at all--you can just make the projection the same size as the label and turn off the 'wrap U... wrap V' attributes. Then map the rest of your texture--the background outside of the label--to the 'default colour' of the file texture. That should produce the desired results.

Best of luck. If you have other questions or want a hand fine tuning a workflow post again.

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 22, 2006 at 1:45:20 am

I aligned the two projection nodes under the 3D Placement node, one attaches the alpha map color to transparancy and the other is the image. I need to use a cylindrical placement, when I activate interactive placement and then try to scale horizontally I can only get one projection to move, it works fine vertically. Was able to position using standard scale but it is less acturate. Does this work for you?

I guess most people do use PSD to layer textures. In this case I am placeing a lable on a 'glass' bottle with a second lable that needs to be independent of the first, so I really needed to layer the texture/shader to get good transparency. Other wise I think you're second solution could work. ( the stencil wouldn't accept a mask image as a projection - might as well move using coord in 2D placement.)

Tried to find a contact for the tutorial book but could not even find an email. I suspect that this is how Maya works and the tutorial is misleading !? Posted a mediocer review on Amazon.




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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 24, 2006 at 8:18:23 pm

Hello again, Tom.

I have just walked through the tutorial in questions, so I can finally--and unfortunately--confirm your findings.

The steps spelled out in the text result in a luminance-driven alpha blending (regardless of the state of the 'Alpha is Luminance' attribute), which makes the bandages themselves partially transparent. The alpha channel of the file texture itself is completely ignored.

The finished example of the scene exhibits exactly the same problem, so it's not just that they left out a step or two--it seems the authors have actually described an incorrect workflow. The alpha channel embedded in a file texture does NOT get passed through the same projection node as its RGB info. The 'outAlpha' output by a projection node will, so far as I can tell, always be generated based on the luminance of the combined colour channels, making it virtually useless.

The only thing I can think of is that they were actually working on a Maya 8 version of the book simultaneously, and this is a feature that exists in Maya 8? In any case, a disappointing and surprising oversight.

Sorry for the long drawn-out hassle, Tom--and I'm also sorry we couldn't find a 'real' solution!

-Steve


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TomKarl
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 27, 2006 at 6:11:49 pm

Steve, I very much appreciate you following through on this.
I am using Maya 8 so its' not a transition thing. How could they be so far off?

I just found an general email address for the learning resources and I'll send an email off to them.

I guess this process doesn't get used much.

Thanks again!


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Steve Sayer
Re: What creates alpha when applying file textures , color or alpha channel?
on Nov 27, 2006 at 9:16:18 pm

No problem, Tom--I was curious to get to the bottom of it, too. I wish I'd hauled out the tutorial myself a lot earlier, though--it makes it pretty obvious where the problem is!

Please post again if you get any response from your email--I'd be very curious to know what they say!

Best of luck with your own projects.

-Steve


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Karsten Mehnert
Re: What creates alpha when applying file textures , color or alpha channel?
on Sep 9, 2011 at 7:52:02 am

Wow! I am using Maya Version 2011 x64 - and it is still the way you are describing. I was looking for a working solution since 3 days now.


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