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alpha channel clipping problem
Posted: 31 July 2017 05:14 PM   [ Ignore ]  
Total Posts:  298
Joined  2010-04-13

Hi Dr. Sassi, my apologizes, I have forgotten, but if I use an image for the color, then the same for alpha channel, I get an"edge around my object. I used to know how to resolve this, but I forgot. Can you please tell me/remind me how to resolve this? I guess I can always create a separate alpha, and “reduce” it so, my color image/model has no edges, but I appeal to the sage, Dr. Sassi, thank you wink-Craig

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Craig

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Posted: 31 July 2017 05:35 PM   [ Ignore ]   [ # 1 ]  
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Hi Craig,

Typically that is a pre-multiply problem. Like to apply an alpha channel on a na already transparent background. (But it can be also a problem of color management.) Well, since I think guessing is not really professional, I have send you na upload link. Please share the scene with the image file to that option.

I will not post the image, only the tiny edge crop perhaps.

Talk to you soon.

All the best

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
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Posted: 31 July 2017 06:38 PM   [ Ignore ]   [ # 2 ]  
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Craig,

Thanks for the file, as usual, files are providing information to share the needed information. grin

Please find in your Cineversity-Private Message a link with a download.

The file was small (504x600 pixels), just 8bit/channel and the “transparent” part was premultiplied. You can see the background in it, but Photoshop shows an premultiplied image. This information is then used twice on the image in C4D, doubles the mask.

That is not nice, but it certainly only added to the problem. There was just too much blue-spill from the sky in the image. If you open the image in Photoshop and use a Image>Calculation on it, e.g., green and blue channel, multiply or difference, pretty much any blend-mode shows that the mask has a lot of problems, even outside of the tree.

To just save the alpha and grow the values back to opaque, for a proper masking, wouldn’t work here at all.

The blue spill needed to be selected and tinted (or masked out, I tinted it, see folder)

After some adjustments in the mask (levels, dodge and burn, as well brush work) the alpha was stored in the psd file.

I took a small sample of the green, average blurred it and used it as background, to avoid fringing. A merge/option visible gave me the resulting layer.

There is more about textures and use of images, see link below [signature] , that I do not repeat all of that again wink

I hope the tree is working now, as much as it can—with the low res.

To have transparence in the layer is normally suggested to be avoided, it will bite, soon or later.

All the best

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
https://www.youtube.com/user/DrSassiLA/playlists

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Posted: 31 July 2017 06:41 PM   [ Ignore ]   [ # 3 ]  
Total Posts:  298
Joined  2010-04-13

thank you, Best, Craig, can ALWAYS count on your sage advice!

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Posted: 31 July 2017 06:51 PM   [ Ignore ]   [ # 4 ]  
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You’re very welcome, Craig.

Since you told me in the PM that it was a 3rd party image, I felt free to critique it in post #2, since the author has been not shared, I think that was OK to do so.

If there is any other image or problem, please ask, I’m really happy to look into it, as I hope that any question here, will support many people on the long run as well.

My best wishes for the project.

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
https://www.youtube.com/user/DrSassiLA/playlists

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