What is the best method for (Textures/Decals) with alphas in 3Dsmax?

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  10 October 2012
What is the best method for (Textures/Decals) with alphas in 3Dsmax?

I created a hard surface modeled figure and want to add decals in a separate texture layer (graphics etc). What is the best method for adding the decals?

I know I have to use to Bitmap inputs (One for the image RGB with the pre-multiplied option disabled) and one for the Alpha (With Mono Channel Output on Alpha). Then use the Alpha in the opacity slot of the material. Only there is a problem with Premultiplied/Not-Premultiplied alphas.

For example I would like to add a worn sticker graphic with multiple colors and an alpha where the sticker is worn. But There will always be multiplication with the background (For example black or white) Can you export a true Non-premultiplied alpha from Photoshop? I tried it with a TGA and PNG with a transparent background in Photoshop but did not get good results.
 
  10 October 2012
Well, as for the projection/placement itself I recently saw this script that might help you out. http://www.scriptspot.com/3ds-max/s...decal-projector

As for the alpha, if you really want non-premultiplied (better known as stright alpha) from Photoshop you should work according to the transparency grid, that means, if you work with the transparency directly (not as a separate channel under the "channels" panel) you are then working "straight".

TGA as well as TIF prefer to have the alpha channel separate from the colour information, which means it becomes premultiplied. What premultiplied actually means is when the background colour is present in the image as a result of the alpha information being in a separated channel. In such case you should check the Premultiplied Alpha checkbox under your Bitmap node in 3dsmax.

If you want to work "straight" you simply leave the transparency grid visible in Photoshop and save it into a format that stores alpha data together with the colour data. While PNG might not be a professional image format per se, it uses the straight alpha information in Photoshop and does not rely on the any channels from the "channel panel". Photoshop documents (PSD) will use straight alpha information naturally, which can be read by 3dsmax as default.
 
  10 October 2012
Thanks, now I understand the difference better between an image format that uses straight alphas (without a separate Alpha channel and other formats where the alpha is in a separate channel (and those formats are therefore naturally premultiplied). I will try using PNG then. I still had some small white borders with PNG though (even with pre-multiplied off).

Last edited by Seph : 10 October 2012 at 12:38 PM.
 
  10 October 2012
I get the best results from tiff exported with an alpha channel, in max premultiplied off. The channel is mono with rgb intensity set.
If you want multiple textures like your worn stuff on a decal you really have three layers. Base material, sticker and then worn effect on top. Use a composite material in max and just add the three materials to the available slots in that composite. I am using it now and it works well.

The alphas you have to monkey about a bit with. I am also using the opacity slot for straight text on a class material that works well too.
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  10 October 2012
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