Alpha file formats

# 1 13-01-2013 , 05:28 AM

Registered User
Join Date: Oct 2010

Posts: 234

Hi.

I'm causing myself a bit of confusion over the best way to create alpha channels. I'm unsure what file format to use, or what works at all.
I used a PNG texture earlier, which by some fluke had its own transparency built in. But I can't this functionality again in other images. I've tried tiff & bmp - no good. I've tried targa but maya crashes every time I try to load it into the hypershade.

Other png's look fine in the viewport, but they won't render.

It's hard to find documentation that explains what file format to use when, and why....

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# 2 13-01-2013 , 07:13 AM

Technical Director
Join Date: Feb 2004

Posts: 2,988

File types are usually picked by three things.

1) Compression
2) Alpha channels
3) Bits per channel

PNG is a good choice, as it's completely lossless, supports alpha channels, and can support up to 16 bits per channel.

TGA is another good choice, as it's completely lossless, supports alpha channels, but can only support 8 bits per channel.

TIFF is another common format, as it has many different compression algorithms, supports alpha channels, and can support up to 32 bits per channel. I'd recommend against it however, as it's not a very well supported format in terms of 3d applications. For example Maya and Max handle them completely differently.

EXR is the extreme of these. You can specify lossless, or lossy compression, supports an arbitrary number of channels, and can support up to 32 bits per channel; however it's manly used to hold displacement or bump maps, as well as rendered output, rather than textures.

Are you wondering how you create an alpha channel in a PNG image? Simply open Photoshop, open your image, in the layers palette click channels, then click on the new layer icon at the bottom. Paint in this channel, and when you're done, click back on RGB in the channels palette, and save your image.

Imagination is more important than knowledge.

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# 3 13-01-2013 , 11:59 AM

Registered User
Join Date: Oct 2010

Posts: 234

thanks for the info Next.

I understand alphas, channels and mask etc. My problem is - .png shows a correctly in the viewport but maya wont render, saying the .png is not a image format. And that Maya crashes everytime I try to pipe a .tga into a new material....

the .png with the 'fluke' alpha doesn't have an alpha channel (least it doesn't show in photoshop) - I rendered a mesh out as .png then dropped that image onto a plane and it used the greyscale image as the alpha and worked perfectly...

Last edited by se7enhedd; 13-01-2013 at 12:02 PM.

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# 4 13-01-2013 , 12:29 PM

Registered User
Join Date: Oct 2010

Posts: 234

well. I just tried another .tga and it worked fine. so it must've been a case of file corruption.

thanks very much for the info tho Next!! user added image

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